Perceived Health and Physical Functioning in Postpoliomyelitis

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Perceived Health and Physical Functioning in Postpoliomyelitis Syndrome: A 6-Year Prospective Follow-Up Study Frans Nollet, MD, PhD, Anita Beelen, PhD, Jos W. Twisk, PhD, Gustaaf J. Lankhorst, MD, PhD, Marianne de Visser, MD, PhD ABSTRACT. Nollet F, Beelen A, Twisk JW, Lankhorst GJ, de Visser M. Perceived health and physical functioning in postpoliomyelitis syndrome: a 6-year prospective follow-up study. Arch Phys Med Rehabil 2003;84:1048-56.

© 2003 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation

Objectives: To study prospectively the health status, and especially the physical functioning, of polio survivors with and without postpoliomyelitis syndrome (PPS), and to identify prognostic determinants of change in physical functioning. Design: Prospective cohort study; measurements at baseline and after 1, 2, and 6 years. Setting: University hospital in the Netherlands. Participants: Seventy-six subjects with PPS and 27 without PPS. Interventions: Not applicable. Main Outcome Measure: The Nottingham Health Profile (NHP) physical mobility category. Results: Subjects with PPS had significantly poorer health status than subjects without PPS. No significant differences in mean NHP physical mobility scores between baseline and 6 years were found; both groups had improved after 1 year, after which there was a slow decline over the next 5 years. During the first 2 years, strength measurements showed little decline that was not related to changes in NHP physical mobility score. A physical performance test revealed no mean change in the first 2 years, but the subgroup with a decline above the 75th percentile eventually deteriorated 10.5!16.3 points on the NHP physical mobility category (P".01) at 6 years from baseline. This subgroup had more extensive paresis than the other subjects, although it was not significant (P".07). The extent of paresis at baseline was the only prognostic determinant for an increase in NHP physical mobility problems after 6 years. Conclusions: Subjects with and without PPS did not differ with regard to changes in health status in a 6-year period. The fact that the extent of paresis was a prognostic factor for a decline in physical functioning is in accord with a (slow) decline in muscle mass, as a late effect of polio, that may lead to a decline in physical functioning as the reduced muscle capacity becomes less able to meet the demands of daily physical activities. Key Words: Health status; Longitudinal studies; Postpoliomyelitis syndrome; Rehabilitation.

N THE PAST 15 YEARS, many polio survivors have exIcreased perienced late-onset neuromuscular symptoms and defunctional abilities. These symptoms, which include

From the Department of Rehabilitation Medicine (Nollet, Beelen) and Department of Neurology, Academic Medical Center, University of Amsterdam, Amsterdam (de Visser); and Department of Rehabilitation Medicine (Lankhorst) and Institute for Research in Extramural Medicine (Twisk), VU University Medical Center, Amsterdam, The Netherlands. Supported by the Prinses Beatrix Fonds, The Hague, The Netherlands. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated. Reprint requests to Frans Nollet, MD, PhD, Dept of Rehabilitation Medicine, Academic Medical Center, University of Amsterdam, P.O. Box 22660, 1100DD Amsterdam, The Netherlands, e-mail: [email protected]. 0003-9993/03/8407-7599$30.00/0 doi:10.1016/S0003-9993(03)00108-4

Arch Phys Med Rehabil Vol 84, July 2003

1-5

new or increased muscle weakness, fatigue, muscle and joint pain, muscle cramps, loss of endurance, problems with swallowing, respiratory insufficiency, and functional loss, have been termed postpoliomyelitis syndrome (PPS).6 The key symptom is new or increased muscle weakness in the absence of other medical conditions that might explain the symptoms. The results of a limited number of prospective follow-up studies have focused mainly on a decrease in muscle strength. No decline in strength was found in 3 studies with follow-ups of 1,7 2,8 and 5 years.9 Other studies have reported a slow decline in muscle strength.10-12 Grimby et al12 reported a 12% to 18% decline in quadriceps strength in “unstable” polio legs and a 1% to 7% decline in “stable” legs over an 8-year period. The classification of polio legs into stable or unstable was made retrospectively, based on the subject’s assessment of whether the legs had become weaker during the study period. Although the number of studies that have shown a decline in muscle strength is very limited, the decline would be in keeping with the observed signs of ongoing denervation of isolated muscle fibers because of terminal axonal degeneration that supposedly results from premature aging of metabolically exhausted motoneurons. The evidence for this has mainly come from electrophysiologic studies.13-17 The main functional problems of patients with PPS are related to physical activities such as walking, climbing stairs, and mobility-related activities of daily life.1,18-21 Only a few prospective studies, all with a follow-up of approximately 5 years,9,18,22 have considered different aspects of functioning in different populations; therefore, it is difficult to make comparisons. The studies have reported increased handicaps in patients with PPS but not in polio survivors who do not have PPS,18 increased use of personal assistance and assistive devices by PPS subjects,22 and even improvement on a walking test in a representative sample of polio survivors that included symptomatic and asymptomatic patients and patients with comorbidity.9 Given the limited data on changes in functional status over time, we investigated prospectively the differences in changes over 6 years in health problems, especially physical mobility problems, between polio survivors with without PPS. Another objective was to investigate whether PPS subjects who reported ongoing progression of muscle weakness during our study would show a greater increase in health problems than PPS subjects who reported stable muscle strength. In the first 2 years of the study, strength and physical performance were measured annually. The predictive value of these measurements was studied by investigating the changes in the measurements and the changes in reported physical mobility problems after 6 years. The ultimate goal was to identify prognostic

PERCEIVED HEALTH CHANGES IN POLIO, Nollet

determinants of the changes over time in physical mobility problems. METHODS Participants One hundred three polio survivors, previously described elsewhere,19 were monitored for 6 years. Seventy-six met the criteria for the diagnosis of PPS according to Halstead and Rossi,6 that is, new or progressive muscle weakness among the reported symptoms and the absence of other medical conditions that might explain the symptoms. Twenty-seven survivors, whose functioning was stable, formed the non-PPS group. The following potential determinants of physical mobility problems were collected at baseline: age, gender, age at acute polio onset, the number of body sites with residual paresis and self-reported walking ability after recovery from acute polio, the duration and number of new neuromuscular symptoms, the duration of new or increased problems with activities of daily living (ADLs), the number of clinically affected body sites identified by physical examination, and the reported walking ability at baseline. The maximum number of body sites was 6: 4 extremities and trunk and bulbar involvement. Self-reported walking ability was divided into 4 distances: less than 250m, 250m to 1km, 1 to 5km, and 5km or more. The new symptoms included muscle weakness, muscle pain, muscle cramps, muscle atrophy, decreased endurance, fatigue, joint pain, cold intolerance, and respiratory problems. The study was approved by the medical ethics committee of the Academic Medical Center, and all subjects gave their written informed consent.

1049

flexors were also measured with MMT. To monitor a change in leg strength over time, an MMT sum score, ranging between 0 and 80, was obtained by adding the values of all 16 lowerextremity muscle groups that were tested. Throughout the study, all MMT measurements were taken by the same investigator, and another investigator took all of the dynamometer measurements. Physical Performance Test The physical performance test consisted of 6 activities: standing up from lying supine on an examination table set at hip heights, walking 10m, rising from a chair (knee angle of 90°), climbing stairs (22 steps), descending stairs, and walking 75m. Subjects were instructed to perform all the activities at maximal speed and were given 3 minutes of recovery time between each activity. The total time (physical performance test time) was calculated in seconds by adding the time scores of the 6 activities. Protocol Measurements were performed at baseline, and after 1, 2, and 6 years. At baseline, and after 1 and 2 years, questionnaires were completed and strength and performance measurements were taken at the Department of Rehabilitation of the Academic Medical Center. If, at the 2-year follow-up, subjects were unwilling to visit the department, they were asked to complete the questionnaires at home and return them by mail. At the 6-year follow-up, all subjects received the questionnaires by mail. If they did not return them within 4 weeks, they were contacted by telephone.

Measurement Instruments Questionnaires. Subjects completed the validated Dutch version of the Nottingham Health Profile23 (NHP), the Polio Problem List19 (PPL), and the Life Satisfaction Questionnaire24 (LSQ). The NHP has 2 parts, with all questions in a yes-no format. The first part (NHP-I) contains 38 questions that measure perceived health status in 6 categories: physical mobility, energy, pain, sleep, social isolation, and emotional reactions. The category scores range from 0 (no complaints) to 100 (answered “yes” to all questions). The score for the physical mobility category (NHP physical mobility) was the primary outcome measure. The second part (NHP-II) assesses whether the actual health status causes difficulties with 7 daily activities. The PPL consists of 16 items, including symptoms, functional problems, and psychologic aspects. It identifies 3 “priority” problems by asking subjects to select their 3 major problems and to rank them in decreasing order of importance. Furthermore, all items are scored on an 8-point scale, ranging from 0 (no problem) to 7 (severe problem). The LSQ measures satisfaction with life in general and satisfaction with 7 aspects of life, on a 6-point scale, ranging form 1 (very dissatisfying) to 6 (very satisfying).

Data Analysis The primary analysis was to compare the changes at the 6-year follow up from baseline in the polio groups, using the paired t test, and the difference in change between the 2 groups with the Student t test. Statistical analysis was performed with the SPSS statistical software package.b An ! level of P less than .05 was used for all tests of significance. To compare the time course between groups, repeated-measurement analysis with general estimated equations28 was performed with the SPIDA software package.c With general estimated equation analysis, all longitudinal data are used, and not just data on complete cases. Furthermore, this method can be applied with unequal time intervals. To describe the time course, the best suitable functions with time (ie, either a linear or a quadratic function) were modeled. For the PPL the scores of the 3 priority problems selected at baseline and the scores for the 4 items with the highest mean score at baseline are presented, whereas the remaining 12 items of the PPL are summarized in 2 mean scores: one score for the problems with daily activities (housekeeping, work, hobbies and recreation, family life, activities around the house, transport, walking indoors, social life, self-care), and the other for aspects of mental distress (anxiety, uncertainty, acceptance). The Cronbach ! was calculated for these averaged scores at baseline.

Strength Measurements Muscle strength was measured with the manual muscle test (MMT), according to the Medical Research Council (MRC) Scale,25 and ranges from 0 (no contraction) to 5 (normal strength); and with the Citec hand-held dynamometera in newtons in the test positions described for this dynamometer.26,27 Hip flexors, hip abductors, knee extensors, knee flexors, and dorsiflexors were tested by both MMT and the dynamometer. The strength of the hip extensors, hip abductors, and plantar-

Secondary Data Analysis During the study, some subjects without PPS developed PPS symptoms. Therefore, the general estimated equation analysis was repeated, with these newly symptomatic non-PPS subjects excluded. This analysis was also done for subgroups of PPS subjects who perceived a further increase in muscle weakness and subjects who reported stable strength during the study. Subgroups were formed to enable a study of the relation between changes in the NHP physical mobility score and the Arch Phys Med Rehabil Vol 84, July 2003

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PERCEIVED HEALTH CHANGES IN POLIO, Nollet Table 1: Subject Characteristics PPS (n"76)

Polio history Age at acute polio (y) Body sites with residual paresis* Walking ability after recovery† Baseline characteristics Age (y) Sex (male/female) New symptoms (yes/no) Duration of new symptoms (y) No. of new symptoms Functional decline (yes/no) Duration of functional decline (y) Walking ability at present† Clinically affected body sites* Legs with paresis (1/2)

3.2!3.8 (0.1–26) 1 (1; 2) 4 (3; 4) 47.9!6.1 (32.6–60.9) 17/59 76 8.4!4.7 6 (5; 7) 74/2 6.6!4.1 2 (1; 3) 2 (1; 2.8) 43/33

Non-PPS (n"27)

2.6!2.0 (0.3–9) 1 (1; 2) 4 (3; 4) 44.6!6.1 (32.5–57.6)‡ 8/19 18/9¶ 3.8!5.5§ 1 (0; 2)! 11/16¶ 1.8!3.0§ 3 (2; 4)! 1 (1; 2) 16/11

NOTE. Values are mean ! standard deviation (SD) or median (25th; 75th percentiles) except for age at acute polio and present age, which are mean ! SD (range). *Range 0 to 6 (4 extremities, trunk, bulbar signs). † Four categories: 0 –250m; 250m–1km; 1–5km; #5km. ‡ P$.05. § P$.001 (Student t test). ! P$.001 (Mann-Whitney U test). ¶ P$.001 ("2 test).

changes in strength and physical performance in the initial 2 years. Based on data from a previous validation study,27 only hand-held dynamometer strength values within the measurement range were included in the analysis. For knee extensors and flexors, this range was between 0 and 160N, and for hip flexors, hip abductors, and dorsal flexors, it was between 0 and 250N. Strength values and physical performance test times are reported for those subjects with valid measurements on all 3 occasions. They were analyzed at 2 years for changes from baseline. To assess the representativeness of these subjects, the data for all subjects at baseline are also reported. A loss in strength, as measured with the dynamometer, was defined as a decline in strength outside the predetermined 95% limits of agreement (LOA) for that muscle group.27 Subjects were divided into 2 groups, with 1 group having no decline and the other having at least 1 muscle group with a decline in strength outside the LOA. For the MMT sum score and the physical performance test, the subgroup of subjects with the largest decline in strength or performance at 2 years from baseline (ie, a decline #75th percentile of the differences for all subjects) was compared with all other of the subjects. Associations were studied with the chi-square test. With general estimated equations, a prognostic model for the NHP physical mobility score was constructed. First, the potential determinants collected at baseline, the diagnosis of PPS, the baseline scores of the PPL items of fatigue and walking outside, the MMT sum, and the physical performance test were entered separately in the best fitting model with time, that is, time and time-squared. Second, the factors with P values below .10 in these models were entered simultaneously in the model and analyzed backward with the criterion to remove values of P less than .10. To check for erroneously omitted factors, each factor that was not retained in the model in the first or second steps of the model-building was again entered separately in the model and retained if its P the value was less than .10. This cycle was repeated each time a factor had to be added to the model. Finally, to determine a prognostic model for changes in the NHP physical mobility score during the follow-up, the Arch Phys Med Rehabil Vol 84, July 2003

interactions with time and (if necessary) time-squared were added to the model. RESULTS Subject Characteristics Subjects with PPS did not differ from subjects without PPS with regard to their polio histories (table 1). The PPS subjects were on average 3.2 years older than the non-PPS subjects (P$.05). Although the subjects without PPS did not experience new or increased muscle weakness, two thirds did report new symptoms, which were fewer in number and were of shorter duration than symptoms reported by the PPS subjects. Forty percent of the subjects without PPS also reported a functional decline, which was also shorter in duration than declines reported by the subjects with PPS. Protocol Adherence Complete follow-up data were obtained for 85 (82.5%) subjects. For the primary analysis of the change at 6 years from baseline, the data from 95 (92%) subjects were available (fig 1). At the 1- and 2-year measurements, 7 and 9 PPS subjects respectively were not prepared to visit our clinic. At 6 years, no data could be collected from 4 subjects with and 4 subjects without PPS. Six did not respond (PPS: 3 women, 1 man; non-PPS: 1 woman, 1 man), 1 woman without PPS had died from an unrelated disease, and another could not be traced. Nottingham Health Profile The health problems after 6 years had not increased in the PPS subjects for any NHP-I category and had decreased significantly on the NHP-II (table 2). The only significant change between the polio groups was in the energy category, in which PPS subjects showed improvement and non-PPS subjects showed deterioration. After the first year, the mean scores for all NHP categories and for the NHP-II were lower in both groups. In general, this was followed by an increase in scores

1051


subjects, the problem severity for the 3 priority items on the PPL at baseline had decreased significantly after 6 years, and there was no increase in any other PPL score (table 3). The subjects without PPS had a significantly increased score after 6 years only for walking outdoors. A significant difference in change from baseline between the 2 groups was found at 6 years with the Student t test, for the problems of fatigue and walking outdoors. Most PPL scores showed an initial improvement in the first year, followed by a slow increase in problem severity during the following years. All scores differed significantly between the 2 groups, whereas the time course differed significantly only for walking outdoors (P".049) (ie, a decrease in the PPS subjects and an increase in the non-PPS subjects) and for the problem area of activities (P".004) (ie, more stable in the non-PPS subjects).

Fig 1. Flow diagram of measurements taken and missing data at the various measurement points.

at 2 and 6 years, and this time-course pattern was best described by a quadratic function. General estimated equation analysis also showed that compared with non-PPS subjects, PPS subjects had significantly higher problem scores for the categories of physical mobility, energy, pain, and sleep, and for the NHP-II. Polio Problem List The Cronbach ! for the 2 problem area scores was good: for activities, it was .84, and for mental distress, it was .87. In PPS

Life Satisfaction Questionnaire No change in satisfaction at 6 years from baseline was found in the 2 groups (table 4). The significant difference in change between groups in 6 years in satisfaction with sexual life, according to the Student t test, was not confirmed in the general estimated equation analysis. With general estimated equations, no change throughout the study period was found in satisfaction with financial situations, partnership relationships, family life, or contacts with friends or acquaintances, whereas most other items showed a slight initial improvement followed by a slow deterioration. Small significant differences between PPS and non-PPS subjects were found for satisfaction in self-care ADL, leisure, and vocational situations. Muscle Weakness In retrospect, 3 non-PPS subjects developed symptoms of new muscle weakness during the study. A comparison of the polio groups with these 3 non-PPS subjects excluded from the analysis did not change the results for the NHP scores. A

Table 2: NHP Scores for Subjects With and Without PPS NHP

NHP-I categories (range, 0–100) Physical mobility PPS Non-PPS Energy PPS Non-PPS Pain PPS Non-PPS Social isolation PPS Non-PPS Emotional reactions PPS Non-PPS Sleep PPS Non-PPS NHP-II (range, 0–7) PPS Non-PPS

Baseline

1 Year

2 Years

6 Years

n

% 6–0 Years

41.4!18.5 23.1!19.5

37.1!17.9 23.1!20.8

38.0!19.3 20.8!20.5

39.8!19.9 27.2!24.9

71 23

&1.8!16.8 4.9!18.0

55.7!37.9 14.8!25.0

35.3!36.6 12.8!23.2

39.9!37.3 22.2!30.7

40.7!36.8 31.9!40.8

72 23

&16.7!35.8*† 17.4!33.1‡

39.8!32.3 17.1!26.0

34.8!31.4 10.6!20.8

36.5!30.5 14.8!24.3

39.7!30.0 16.8!25.5

69 23

1.4!27.2 2.7!18.1

6.3!12.3 5.2!17.2

3.5!9.0 2.3!6.5

3.9!11.3 2.2!8.5

4.8!15.7 2.6!9.2

71 23

&1.1!12.1 0.0!12.1

12.7!17.5 10.7!17.6

6.6!11.5 6.0!15.8

9.9!17.0 4.9!11.7

8.9!15.0 6.8!16.7

71 23

&3.4!18.0 &2.9!12.6

25.0!30.3 13.3!24.2

19.4!28.1 7.7!16.1

19.7!26.4 11.1!25.0

24.2!29.6 12.2!23.9

72 23

&1.9!25.2 &0.9!19.5

3.0!1.8 1.2!1.4

2.1!1.8 0.8!1.1

2.5!1.8 0.7!0.8

2.4!1.7 1.0!1.7

68 23

&0.6!1.9† 0.0!2.2

NOTE. All values are mean ! SD. *P$.005 (Student t test; PPS vs non-PPS). † P$.05 (change from baseline within group; paired t test). ‡ P$.005 (change from baseline within group; paired t test). Arch Phys Med Rehabil Vol 84, July 2003

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PERCEIVED HEALTH CHANGES IN POLIO, Nollet Table 3: Polio Problem List Scores for Subjects With and Without PPS Polio Problem List

Priority problems Problem 1 PPS Non-PPS Problem 2 PPS Non-PPS Problem 3 PPS Non-PPS Item scores Fatigue PPS Non-PPS Walking outdoors PPS Non-PPS Climbing stairs PPS Non-PPS Pain PPS Non-PPS Problem areas Activities PPS Non-PPS Mental distress PPS Non-PPS

Baseline

1 Year

2 Years

6 Years

n

% 6–0 Years

5.8!1.3 4.6!1.8

4.8!1.6 4.1!1.9

4.9!1.9 3.6!1.9

5.1!1.6 4.3!2.1

71 23

&0.8!1.8‡ &0.2!1.8

5.2!1.6 3.9!1.9

4.5!1.7 3.3!2.0

4.7!1.5 3.0!1.7

4.6!1.6 3.3!2.1

71 23

&0.7!1.9‡ &0.5!2.8

4.7!1.4 3.4!1.8

3.5!2.1 2.8!2.0

3.8!1.9 2.7!1.9

4.4!2.0 2.8!2.2

72 23

&0.7!2.0† &0.4!1.9

5.2!1.6 3.3!1.9

4.6!1.6 3.4!1.8

4.7!1.7 2.8!1.9

4.9!1.6 3.9!1.7

72 23

&0.4!1.7* 0.6!1.6

4.8!1.7 2.6!2.6

4.4!1.5 3.5!2.3

4.5!1.7 2.7!2.2

4.5!1.7 3.7!2.3

72 23

&0.2!1.6* 0.9!2.0†

4.8!1.8 2.9!2.4

4.0!2.2 2.8!2.2

4.3!2.0 2.8!2.4

4.5!1.8 3.2!2.5

71 23

&0.3!2.0 0.4!1.6

3.3!2.2 2.2!2.0

3.0!1.9 1.9!2.0

3.2!2.1 1.9!1.9

3.7!1.9 2.2!2.0

72 23

0.4!1.9 0.1!2.2

2.3!1.3 0.9!1.0

1.6!1.3 1.1!0.9

2.0!1.3 1.1!1.0

2.3!1.3 1.1!1.2

56 20

0.0!1.2 0.2!0.9

2.5!2.0 1.5!1.9

1.6!1.5 1.1!1.4

2.1!1.9 1.2!1.6

2.2!1.7 1.3!1.5

71 23

&0.4!1.8 0.2!0.9

NOTE. All values are mean ! SD. *P$.05 (Student t test; PPS vs non-PPS). P$.05 (change from baseline within group; t test). ‡ P$.005 (change from baseline within group; t test). †

further increase in muscle weakness was perceived by 45 PPS subjects, whereas muscle weakness remained stable in 26. One PPS subject did not answer this question. The NHP physical mobility score of the PPS subjects who reported progression of muscle weakness was 7.8 points worse than the score for the PPS subjects with stable muscle weakness (general estimated equations, P".051). There was no difference in time course between the subgroups and no differences in score or in change between the subgroups for any other NHP category or the NHP-II. Manual Muscle Testing With the paired t test, no decline in MMT sum score at 2 years from baseline was found in the PPS subjects, whereas the non-PPS subjects showed a small but significant decline of 1.1 point (table 5). However, analyzed with general estimated equations, the rate of decline in the MMT sum score during the initial 2 years of the study was .25 per year (P".02), and the decline in score did not differ between groups. Ten PPS (15%) and 6 non-PPS (23%) subjects had a decline in the MMT sum score of at least 2 points at 2 years from baseline, that is, a decline greater than the 75th percentile. These percentages did not differ significantly between the groups. A decline in the MMT sum score of at least 2 points was not associated with progressive muscle weakness. There were no significant differences in change for the NPH physical mobility score beArch Phys Med Rehabil Vol 84, July 2003

tween subjects with or without a decline in MMT sum of at least 2 points. Hand-Held Dynamometry Fifty-nine percent of the hand-held dynamometry measurements were within the valid measurement range both at baseline and at the 2-year follow-up, and 26% of the measurements were outside the valid range on at least 1 occasion. Measurements could not be obtained in 10% of the muscles because of paralysis and in 2% because of joint arthrodesis. Recordings were missing at least once in 3% of measurements because of pain or muscle cramps. No significant decline in mean handheld dynamometry strength over 2 years was found for any muscle group tested. The mean hand-held dynamometry strength of 2 muscle groups in the PPS subjects had actually improved significantly (table 5). Overall, the change in hand-held dynamometry strength could be calculated for 552 muscles. In 31 muscles (5.6%), the decline in strength was outside the 95% LOA.27 Twenty-seven of the 31 muscles were very weak, with a strength below the 5th percentile of normal values.26 A decline in strength outside the LOA in at least 1 lower-extremity muscle group was found in 18 PPS (27%) and 6 non-PPS (22%) subjects. These percentages did not differ significantly between the groups. The identification of a muscle group with a hand-held dynamometer strength decline outside the LOA was not associated with the

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PERCEIVED HEALTH CHANGES IN POLIO, Nollet Table 4: LSQ Scores for Subjects With and Without PPS LSQ items (range, 1–6)

Life as a whole PPS Non-PPS Self-care ADL PPS Non-PPS Leisure PPS Non-PPS Vocational situation PPS Non-PPS Financial situation PPS Non-PPS Sexual life PPS Non-PPS Partnership relations PPS Non-PPS Family life PPS Non-PPS Contacts with friends/ acquaintances PPS Non-PPS

Baseline

1 Year

2 Years

6 Years

n

% 6–0 Years

4.7!0.9 5.0!1.1

4.9!0.7 5.2!0.7

4.9!0.7 5.1!1.0

4.9!0.8 4.9!0.9

72 22

0.1!1.0 &0.3!0.9

5.1!0.9 5.6!0.5

5.3!0.6 5.5!0.5

5.2!0.8 5.4!1.0

5.1!0.8 5.3!0.9

72 23

0.0!1.0 &0.3!0.9

4.3!1.3 4.9!1.1

4.7!1.3 5.1!1.0

4.5!1.2 5.0!1.3

4.4!1.2 4.9!1.1

72 23

0.2!1.3 &0.3!1.3

3.9!1.4 4.7!1.3

4.3!1.3 4.8!1.4

4.4!1.4 4.5!1.5

4.0!1.4 4.3!1.6

54 20

0.2!1.6 &0.4!1.6

4.9!1.3 4.7!1.5

4.7!1.3 5.0!1.4

4.9!1.1 5.0!1.0

5.0!0.8 4.7!1.2

72 23

0.1!1.1 0.0!1.2

4.6!1.4 4.8!1.4

4.7!1.3 5.0!1.3

4.7!1.2 5.0!1.3

4.5!1.2 4.4!1.3

66 22

0.0!1.4 &0.5!1.0*

5.1!1.2 5.0!1.4

5.1!1.1 5.3!0.9

5.3!0.8 5.3!1.0

5.1!1.1 5.0!1.2

57 21

0.0!1.4 0.0!0.9

5.1!1.1 5.2!1.0

5.3!0.8 5.2!0.8

5.3!0.7 5.2!0.9

5.1!0.8 5.0!1.0

65 22

0.0!1.2 &0.3!0.8

4.9!1.0 5.2!0.9

5.1!0.7 5.3!0.9

4.9!0.9 5.3!0.9

4.9!0.9 5.1!0.9

72 23

0.1!1.0 &0.3!0.9

NOTE. All values are mean ! SD. *P$.05 (Student t test; PPS vs non-PPS).

symptom of increasing muscle weakness. No differences were found between subjects with and without a hand-held dynamometer decline in strength outside the LOA with regard to the change in MMT sum score after 2 years or the change in NHP physical mobility score after 6 years. Physical Performance Test We found no decline in either group in physical performance at 2 years from baseline (table 5). From the baseline values of all subjects, it seemed that the 14 PPS subjects who dropped out in 1 or more of the follow-up measurements represented the worst cases of physical performance. General estimated equation analysis confirmed that the PPS subjects needed more time for the performance test than did the non-PPS subjects, and that the performance of the PPS subjects increased slightly (&1.8s/y), whereas that of the non-PPS subjects remained unchanged. The group of subjects with a decline of 3.75 seconds or more on the performance test in 2 years, that is, above the 75th percentile, was further studied. Sixteen PPS (27%) and 5 non-PPS (19%) subjects showed an increase of more than 3.75 seconds in performance time. These percentages did not differ significantly between the groups. No associations were found between an increase of more than 3.75 seconds in performance time and increasing muscle weakness, a decline in the MMT sum score of at least 2 points, or a hand-held dynamometer decline in strength outside the LOA. However, in the subjects whose performance time increased more than 3.75 seconds, physical mobility problems on the NHP increased significantly, from 38.7!11.1 at baseline to 49.3!16.9 at 6 years (P".01). There was no change in the

other subjects (from 31.5!19.4 at baseline to 30.2!19.0 at 6y; fig 2). The difference in NHP physical mobility between the 2 groups at baseline was significant (P$.05). The physical performance time at baseline for subjects whose performance time increased by more than 3.75 seconds was 85.6!33.4 seconds, which did not differ significantly from the test time of 84.4!47.9 seconds in the other subjects. However, the subjects whose performance time increased had more severe paresis at baseline, with an MMT sum score of 62.0!12.5 compared with 67.7!12.1 for the other subjects; this difference did not reach statistical significance (P".07). Prognostic Determinants Of the 15 potential determinants of the NHP physical mobility score, 10 were significant factors (P#.01) when entered separately with time and time-squared in a longitudinal general estimated equations model. The 10 were walking ability after recovery from polio, diagnosis of PPS, duration of new symptoms, number of new symptoms, duration of new functional decline, walking ability at baseline, PPL item fatigue, PPL item walking outside, MMT sum score, and the physical performance test time. Eventually, a prognostic model for the NHP physical mobility score was obtained (table 6). The number of new symptoms was a significant factor in this model, whereas the diagnosis of PPS was not present in the final model. The MMT strength sum score appeared to be the only prognostic factor for changes in the NHP physical mobility score, as indicated by the significant interactions with time and timesquared. However, the effect of the MMT sum score on the decline in NHP physical mobility was limited: 10 points less on Arch Phys Med Rehabil Vol 84, July 2003

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PERCEIVED HEALTH CHANGES IN POLIO, Nollet Table 5: Muscle Strength and Performance Test for Subjects With and Without PPS All Subjects

Muscle Strength and Performance Test

MMT Sum score legs Hand dynamometry (N) Hip flexion L Hip flexion R Hip abduction L Hip abduction R Knee extension L Knee extension R Knee flexion L Knee flexion R Dorsiflexion L Dorsiflexion R Physical performance test time (s)

Subjects With Complete Follow-Up

n

Baseline

n

Baseline

1 Year

2 Years

% 2–0 Years

PPS Non-PPS

76 26

66.6!12.0 64.3!13.7

65 26

67.1!11.6 64.3!13.7

67.1!11.3 64.3!13.9

66.9!11.6 63.3!14.5

&0.3!2.0 &1.1!2.2*

PPS Non-PPS PPS Non-PPS PPS Non-PPS PPS Non-PPS PPS Non-PPS PPS Non-PPS PPS Non-PPS PPS Non-PPS PPS Non-PPS PPS Non-PPS PPS Non-PPS

68 19 66 20 66 13 67 18 39 11 47 13 59 17 58 15 48 15 49 14 74 27

169!53 196!43 150!54 167!58 165!55 176!58 154!62 170!70 84!47 78!57 67!47 68!53 86!38 103!46 76!41 83!46 152!64 153!70 133!56 170!67 94.7!53.3 74.7!35.2

48 13 46 15 46 10 48 11 23 6 29 8 40 14 42 15 28 10 33 10 60 26

173!49 176!38 144!52 150!55 162!55 173!54 147!60 150!54 63!40 48!27 54!31 54!38 83!40 104!41 80!37 83!46 137!65 134!73 127!51 134!73 88.4!47.8 73.5!35.3

179!53 175!58 162!56 165!65 170!59 181!60 153!66 142!67 72!40 56!35 68!46 60!52 85!42 107!41 88!39 85!48 156!72 141!79 128!57 141!79 85.9!43.4 77.3!37.4

175!54 176!46 157!60 164!66 163!57 166!60 143!60 124!65 64!39 59!45 65!44 61!56 81!40 100!34 83!38 84!53 148!73 153!66 135!54 153!66 86.0!45.0 73.6!35.8

1!28 0!26 13!24† 14!39 0!35 &6!20 &4!30 &26!45 1!19 11!32 11!24* 8!24 &2!19 &4!16 3!17 1!21 11!44 19!38 9!34 19!38 &2.4!10.7 0.2!5.4

NOTE. All values are mean ! SD. Abbreviations: L, left; R, right. *P$.05 (change from baseline within group; paired t test). † P$.005 (change from baseline within group; paired t test).

the MMT sum score at baseline resulted in an increase of 3 points on the NHP physical mobility score after 6 years. DISCUSSION This study focused on the course of changes over time in perceived health problems of PPS subjects compared with non-PPS subjects. The differences between the 2 groups have been described elsewhere.19 There was little change in perceived health problems, measured with the NHP, the PPL, or the LSQ in 6 years in either group of subjects. Some significant changes were found with paired t tests, all of which were related to improvements in the PPS group and declines in the non-PPS group. These statistically significant changes may reflect true changes, but could also be coincidental findings resulting from multiple testing, for instance, with regard to the decrease in satisfaction with one’s sex life found in the nonPPS subjects, or the changes could be because of the phenomenon of regression to the mean, for instance, with regard to the improvement of the PPS subjects on the PPL items, for which the initial scores were very high. It is also conceivable that the subjects with PPS adapted their lifestyle to their physical abilities during the study, resulting in a decline in perceived problems although the NHP showed no improvement in their physical functioning. For the NHP category of energy and the PPL item of walking outdoors, the repeated-measures analysis showed significant differences in the changes over time between the 2 groups. Increasing scores after 6 years for the non-PPS subjects may have resulted from the development of new neuromuscular symptoms during the study. However, this is not supported by Arch Phys Med Rehabil Vol 84, July 2003

the fact that only 3 non-PPS subjects believed that their muscle strength had declined during the study, and thus might have become PPS subjects.

Fig 2. Mean NHP physical mobility scores for the subjects with a decline of 3.75 seconds or more (E) and for the remainder of subjects (●). NOTE. The vertical bars represent the standard error of the mean.

PERCEIVED HEALTH CHANGES IN POLIO, Nollet Table 6: Prognostic Model for the NHP Physical Mobility Score Dependent NHP Physical Mobility (0–100)

R2".58

Predictors

B (95% CI)

Constant Time (y) Time-squared (y2) Age at acute polio (y) No. of new symptoms (0–9) PPL item walking outside (0–7) Physical performance test time (s) MMT sum score (0–80) MMT sum score ' time MMT sum score ' time-squared

5.300 (&10.10 to 20.70) 8.335 (0.82–15.85) &0.862 (&2.19 to 0.47) 1.037 (0.51–1.56) 0.886 (0.02–1.75) 4.861 (3.67–6.05) 0.081 (0.03–0.14) &0.070 (&0.27 to 0.13) &0.164 (&0.28 to &0.05) 0.019 (0.00–0.04)

.491 .027 .194 .000 .041 .000 .003 .481 .004 .048

Abbreviation: CI, confidence interval.

Almost all perceived health problems improved in the first year of the study, perhaps because of improved coping skills or therapy, most PPS subjects received some form of physiotherapy that resulted in less fatigue and functional improvement. However, because there was improvement in both groups, it may also signify bias from participation in the study. For instance, subjects may have overrated the severity of their health problems at baseline, and the medical attention they received during the study may have been reassuring. In line with the slow progressive nature of late polio symptoms, the severity of most health problems slowly increased in the following 5 years. Paired t tests, which compared values at baseline and after 6 years, overlook this dynamic aspect in the development of health problems over time. Concluding, on the basis of these tests, that health status remained stable may therefore be misleading. Although an increase in disability and handicaps related to late polio symptoms has been reported,3,5 no other prospective studies using repeated testing are available for comparison with our results. Because Grimby et al12 reported that muscle strength declined more in unstable muscles than in stable muscles, we thought it important to investigate whether this would also apply to changes in physical functioning over time. However, although physical functioning as measured with the NHP was worse in subjects with unstable muscle weakness than in those with stable muscle weakness, the symptom of progressive muscle weakness was not associated with a more rapid decline in physical functioning after 6 years. The prognostic value of monitoring strength and physical performance annually for 2 years was also evaluated. Two methods were used to measure strength. An MMT sum score was calculated to identify a decline if 1 or more of the examined muscles became weaker. The rate of decline was only .25 points a year, and did not differ between PPS and non-PPS subjects. Although it is well known that the MMT’s ability to detect a change over time is limited,29 this decline was less than the decline of 1 point per year reported by Dalakas et al,10 which may have been because of differences between the 2 studies. For instance, in their study, fewer MRC grades were considered, more muscle groups were measured, the follow-up was longer, and the investigators changed during the study period. Because repeated MMT measurements over a 2-year period did not identify any subgroup with a different change in NHP physical mobility score after 6 years, individual changes in MMT strength at 2 years have no prognostic value for changes in perceived physical functioning, and appear to be measurement errors.

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Strength was also measured with a hand-held dynamometer to obtain a more accurate measurement.30 We had a particular interest in monitoring the strength of individual symptomatic muscles, because group analysis of the mean changes in strength of a particular muscle may obscure a decline in some individuals if that muscle is not symptomatic in the majority of subjects in the group. Unfortunately, the hand-held dynamometer has its limitations when used with polio subjects, as has been shown before: the measurement range has an upper limit and only large individual declines in strength can be detected.27 In 24 subjects, a decline in strength was found in 1 or more lower-extremity muscle groups outside the 95% LOA. Such a change might be considered a true decline. However, these observations were probably not signifying a true decline, because only 5.6% of the valid measurements were outside these limits, which is a little over the 2.5% of observations that statistically could be expected to show a decline outside the LOA. Also, most of these changes were found in very weak muscles, for which small absolute differences in strength easily become large when expressed as percentages.31,32 Further, a hand-held dynamometer decline in strength outside the LOA at 2 years was not related to the presence of PPS, and was of no prognostic value for changes in the NHP physical mobility score. There was no decline in physical performance, in fact, the PPS subjects showed improvement. This improvement, which has also been reported by Windebank et al9 in a walking test, might have resulted from a learning effect or from less fatigue. However, the subjects with the largest decline in performance over 2 years showed more decline in NHP physical mobility after 6 years than did the other subjects. The time needed for the test at baseline did not differ between the 2 subgroups, but the muscle strength measured with MMT differed almost significantly. Thus, it seems likely that the subjects who showed a decline in the performance test were performing at relatively higher levels of their muscular capacity.33 The decline in physical functioning in these subjects may therefore result from overuse.34,35 We built a prognostic model of physical functioning based on the information available at baseline. Interestingly, it was not the diagnosis of PPS, but the number of new symptoms, that was a significant factor in this model. This may be because of the nonspecific nature of the new symptoms themselves, including new muscle weakness that was the key symptom for the diagnosis of PPS.36,37 The development of more new symptoms simultaneously was found to be more specific for late effects of poliomyelitis.37 It may be hypothesized that more symptoms signify more overuse of the remaining muscle capacity, and are therefore related to more limitations in physical functioning. Interestingly, the extent of paresis, as measured with the MMT sum score, was the only prognostic factor for a decline in physical functioning after 6 years. The decline in physical functioning related to the degree of paresis was limited, possibly because in subjects with more widespread paresis, small changes in strength may have functional consequences. They have limited ability to adapt with new functional solutions by using other muscles. Another explanation could be that, in more severe paresis, the number of remaining motor units is more limited and these units have adapted to a greater extent.38 A late deterioration of motor units in these cases might proceed more rapidly and even have an earlier onset.17 The model should be interpreted with caution, because it contains time and time-squared as factors caused by the initial improvement in the first year. In a further follow-up, this model will probably no longer apply, and a linear declining model of physical functioning will be more probable. Arch Phys Med Rehabil Vol 84, July 2003

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CONCLUSION Perceived health status, especially physical functioning, measured with the NHP, showed little change in a 6-year prospective follow-up of subjects with and without PPS. This was partly the result of an unexpected improvement in the first year. Because of the slow decline in strength, in comparison with the measurement error, prospective MMT and hand-held dynamometer strength measurements during a 2-year period had no additional prognostic value for identifying people with a more rapid decline in physical functioning. Although prospective functional tests provide no information about the changes in muscle function over time, their prognostic value for changes in physical functioning in daily life are promising and warrant further study. Regardless of the unobserved decline in functioning and strength during the years before the study, both the subgroup analysis of the changes in time needed for the performance test and the prognostic model suggest that a further decline in physical functioning over time depends mainly on the remaining muscle capacity. References 1. Halstead LS, Rossi CD. New problems in old polio patients: results of a survey of 539 polio survivors. Orthopedics 1985;8: 845-50. 2. Windebank AJ, Daube JR, Litchy WJ, et al. Late sequelae of paralytic poliomyelitis in Olmsted County, Minnesota. In: Halstead LS, Wiechers DO, editors. Research and clinical aspects of the late effects of poliomyelitis. White Plains: March of Dimes Birth Defects Foundation; 1987. p 27-38. 3. Ramlow J, Alexander M, LaPorte R, Kaufmann C, Kuller L. Epidemiology of the post-polio syndrome. Am J Epidemiol 1992; 136:769-86. 4. Lonnberg F. Late onset polio sequelae in Denmark. Results of a nationwide survey of 3,607 polio survivors. Scand J Rehabil Med 1993;28(Suppl):1-32. 5. Ivanyi B, Nollet F, Redekop WK, et al. Late onset polio sequelae: disabilities and handicaps in a population-based cohort of the 1956 poliomyelitis outbreak in The Netherlands. Arch Phys Med Rehabil 1999;80:687-90. 6. Halstead LS, Rossi CD. Post-polio syndrome: clinical experience with 132 consecutive outpatients, In: Halstead LS, Wiechers DO, editors. Research and clinical aspects of the late effects of poliomyelitis. White Plains: March of Dimes Birth Defects Foundation; 1987. p 13-26. 7. Agre JC, Rodriquez AA. Neuromuscular function in polio survivors at one-year follow-up. Arch Phys Med Rehabil 1991;72:7-10. 8. Ivanyi B, Nelemans PJ, de Jongh R, Ongerboer de Visser BW, de Visser M. Muscle strength in postpolio patients: a prospective follow-up study. Muscle Nerve 1996;19:738-42. 9. Windebank AJ, Litchy WJ, Daube JR, Iverson RA. Lack of progression of neurologic deficit in survivors of paralytic polio: a 5-year prospective population-based study. Neurology 1996;46: 80-4. 10. Dalakas MC, Elder G, Hallett M, et al. A long-term follow-up study of patients with post-poliomyelitis neuromuscular symptoms. N Engl J Med 1986;314:959-63. 11. Grimby G, Hedberg M, Henning GB. Changes in muscle morphology, strength and enzymes in a 4-5-year follow-up of subjects with poliomyelitis sequelae. Scand J Rehabil Med 1994;26:12130. 12. Grimby G, Stalberg E, Sandberg A, Stibrant Sunnerhagen K. An 8-year longitudinal study of muscle strength, muscle fiber size, and dynamic electromyogram in individuals with late polio. Muscle Nerve 1998;21:1428-37. 13. Wiechers DO, Hubbell SL. Late changes in the motor unit after acute poliomyelitis. Muscle Nerve 1981;4:524-8. 14. Wiechers DO. New concepts of the reinnervated motor unit revealed by vaccine-associated poliomyelitis. Muscle Nerve 1988; 11:356-64.

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15. Ivanyi B, Ongerboer de Visser BW, Nelemans PJ, de Visser M. Macro EMG follow-up study in post-poliomyelitis patients. J Neurol 1994;242:37-40. 16. Stalberg E, Grimby G. Dynamic electromyography and muscle biopsy changes in a 4-year follow-up: study of patients with a history of polio. Muscle Nerve 1995;18:699-707. 17. McComas AJ, Quartly C, Griggs RC. Early and late losses of motor units after poliomyelitis. Brain 1997;120:1415-21. 18. Grimby G, Jonsson AL. Disability in poliomyelitis sequelae. Phys Ther 1994;74:415-24. 19. Nollet F, Beelen A, Prins MH, et al. Disability and functional assessment in former polio patients with and without postpolio syndrome. Arch Phys Med Rehabil 1999;80:136-43. 20. Thoren-Jonsson AL, Hedberg M, Grimby G. Distress in everyday life in people with poliomyelitis sequelae. J Rehabil Med 2001; 33:119-27. 21. Thoren-Jonsson AL, Grimby G. Ability and perceived difficulty in daily activities in people with poliomyelitis sequelae. J Rehabil Med 2001;33:4-11. 22. Stanghelle JK, Festvag LV. Postpolio syndrome: a 5-year followup. Spinal Cord 1997;35:503-8. 23. Erdman RA, Passchier J, Kooijman M, Stronks DL. The Dutch version of the Nottingham Health Profile: investigations of psychometric aspects. Psychol Rep 1993;72:1027-35. 24. Bra¨ nholm I, Eklund M, Fugl-Meyer KS, Fugl-Meyer AR. On work and life satisfaction. J Rehabil Sci 1991;4:29-34. 25. Medical Research Council. Aids to the examination of the peripheral nervous system. London: Her Majesty’s Stationery Office; 1976. 26. van der Ploeg RJ, Fidler V, Oosterhuis HJ. Hand-held myometry: reference values. J Neurol Neurosurg Psychiatry 1991;54:244-7. 27. Nollet F, Beelen A. Strength assessment in postpolio syndrome: validity of a hand-held dynamometer in detecting change. Arch Phys Med Rehabil 1999;80:1316-23. 28. Zeger SL, Liang KY. Longitudinal data analysis for discrete and continuous outcomes. Biometrics 1986;42:121-30. 29. Beasley WC. Quantitative muscle testing: principles and applications to research and clinical services. Arch Phys Med Rehabil 1961;42:398-425. 30. Schwartz S, Cohen ME, Herbison GJ, Shah A. Relationship between two measures of upper extremity strength: manual muscle test compared to hand-held myometry. Arch Phys Med Rehabil 1992;73:1063-8. 31. Nollet F, Horemans H, Beelen A. A multicenter, randomized, double-blinded trial of pyridostigmine in postpolio syndrome [letter]. Neurology 2000;55:899-901. 32. Agre JC, Herbison GJ. Strength changes over time among polio survivors [letter]. Arch Phys Med Rehabil 2000;81:1538. 33. Nollet F, Beelen A, Sargeant AJ, de Visser M, Lankhorst GJ, de Jong BA. Submaximal exercise capacity and maximal power output in polio subjects. Arch Phys Med Rehabil 2001;82:1678-85. 34. Bennett RL, Knowlton GC. Overwork weakness in partially denervated skeletal muscle. Clin Orthop 1958;12:22-9. 35. Perry J, Barnes G, Gronley JK. The postpolio syndrome: an overuse phenomenon. Clin Orthop 1988;Aug(233):145-62. 36. Rekand T, Albrektsen G, Langeland N, Aarli JA. Risk of symptoms related to late effects of poliomyelitis. Acta Neurol Scand 2000;101:153-8. 37. Aurlien D, Strandjord RE, Hegland O. The postpolio syndrome—a critical comment to the diagnosis. Acta Neurol Scand 1999;100:76-80. 38. Einarsson G, Grimby G, Stalberg E. Electromyographic and morphological functional compensation in late poliomyelitis. Muscle Nerve 1990;13:165-71. Suppliers a. CIT Technics BV, Bieslookstr 25, 9731 HH Groningen, The Netherlands. b. Version 10.0.5; SPSS Inc, 233 S Wacker Dr, 11th Fl, Chicago, IL 60606. c. Version 6.05; Macquarie University, Balaclava Rd, North Ryde, Sydney, NSW 2109, Australia.