Sep 24, 1987 - cerebral syphilitic meningitis. (n = 3), cerebral syphilitic vasculitis (n = 4), tabes dorsalis (n = 1), dementia paralytica (n = 2), and tabo- paralysis.
CLIN. CHEM. 34/4, 665-667 (1988)
CerebrospinalFluid lgG and 1gMIndexes as Indicatorsof Active Neurosyphilis E. A. H. Hleche,’ HelmiAT
J. A. Tutuarlma,’
E. Ch. Wolters,2
L van Trotsenburg,3 R. V. W. van Eylc,4 J. D. Bos,5A. Nbert,6 and H. J. van der
Serological and non-serological tests were performed in matched samples of cerebrospinalfluidand serum from 236 syphilitic patients. An increased lgG or lgM index, or both, was found about 70 times more often in symptomatic neurosyphilis than in latent syphilis without involvement of the central nervous system. An increased Ig index, together with a cell count >5/4., was only found in symptomatic neurosyphilis. Although the numbers of data are small, we conclude
that the igG and 1gM indexes are valuable tests in the diagnosis of syphiliticinvolvement of the central nervous system. AdditionalKeyphrases:likelihood ratio
predictivevalue
According to the World Health Organization (WHO) (1) the traditional criteria for involvement of the central nervous system (CNS) in syphilis are: a positive VI)RL (Venereal Diseases Research Laboratory) test, pleocytosis, and an increased concentration of protein in cerebrospinal fluid (CSF). The VDRL test is not a reliable indicator because it gives a negative test result in 30% to 57% of the patients with active neurosyphilis (1). Pleocytosis and increased protein are signs of unflsmmsition, and are not specific for syphilitic involvement of the CNS (1). The present study was performed to evaluate some CSF tests as indicators for syphilitic CNS involvement. We estimated test characteristics (true-positive rate, true-negative rate), likelthood ratios of positive test results, and predictive values.
Materials and Methods Subjects
Matched CSF and serum samples were obtained from 236 syphilitic patients. All samples were screened for antibodies to human immunodeficiency virus (H1V); positive samples were discarded from the study (n = 11). Samples were also excluded if nonveneric treponematosis (n 3), intravenous penicillin treatment (n = 10), or other (neurologic) diseases (n = 6) were suspected. Departments of’ Clinical Chemistry,Neurology,
Derma-
tology of the Academic Hospital, University of Amsterdam, Mei-
bergdreef 9, 1105 AZ Amsterdam, The Netherlands. 2Departznent of Neurology, Academic Hospital, Vre Umversiteit, Amsterdam, The Netherlands. 4National Institute of Public Health and Environmental Hygiene, Bilthoven, The Netherlands. 6Department of Medical Computing, University of Liege, Liege, Belgium. 7Address correspondence to this author. 8Nonstandard abbreviations: WHO, World Health Organization; CNS, central nervous system; VDRL, Venereal Diseases Research Laboratory; CSF, cerebrospinal fluid; liv, human immunodeficiency virus; FI’A-ABS, fluorescent treponemal antibody absorption; TPHA, Treponemapall idum hemagglutination assay; WI, T. pallidum immobilization; TPR, true-positive rate; ThR, true-negative rate; LR, likelihood ratio; PV+, predictive value of a positive test result. Received September 24, 1987;accepted January 14, 1988.
CSF samples containing more than 150 erythrocytes per microliter were not used (n = 3). We studied two groups of patients: #{149} Those with latent syphilis without CNS involvement (n = 75), i.e., patients with asymptomatic seroreactive syphilis in which CSF treponemal reactivity is negative (1). Latent syphilis means no clinical evidence of active syphilis of any system.
#{149} Those with symptomatic neurosyphilis (n = 13), denoted by the development of neurological signs and (or) symptoms of syphilitic meningovasculitis and (or) parenchymateous neurosyphilis in patients with latent syphilis. The first group comprised 23 women (ages 21-84 years, mean 37, median 33) and 52 men (ages 20-59 years, mean 36, median 35). The second group comprised three women (ages 57-79 years, mean and median 68) and 10 men (ages 38-82 years, mean and median 56), who displayed the following neurosyphilitic syndromes: cerebral syphilitic meningitis (n = 3), cerebral syphilitic vasculitis (n = 4), tabes dorsalis (n = 1), dementia paralytica (n = 2), and taboparalysis (n = 3). The remaining 115 patients (not studied here) were patients with positive treponemal reactivity in their CSF. Procedures Serological tests: All CSF and serum samples were investigated with the VDRL test, the FFA-ABS (fluorescent treponemal antibody absorption) test, the I9SUgM)-FFAABS test, and the TPHA (Treponemapallidum hemagglutination assay; Japan Lyophilization Company). The CSFTPHA results were considered positive if samples were reactive at a fourfold dilution. For the FFA-ABS and the 19S (IgM)-FFA-ABS tests, we used CSF samples diluted fivefold in phosphate-buffered isotonic saline (pH 7.2, containing phosphate, 10 mmol/L, and NaCl, 150 mmol/L). In addition, we investigated serum samples with the WI (T. pallidum immobilization) test. Nonserological tests: We performed CSF cell counts in triplicate in a Fuchs-Rosenthal counting chamber. The protein content was estimated with a Coomassie Briffiant Blue method (Microprotein Rapid Stat Diagnostic Kit; Lancer, Kildare, Ireland) (2). Albumin and IgG in CSF and serum were quantitatively determined turbidimetrically (3); 1gM was quantified by fluoroimmunoassay (4). The albumin mass ratio-albumin in CSF (x 103)/albumin in serum-was used as a test for the integrity of the bloodbrain barrier (5). IgG and 1gM indexes were calculated from CSF/serum ratios of IgG or 1gM and albumin concentrations, by the following formulas: IgG index
1gM index
[IgG]85. [IgG] =
[1gM] CSF [1gM]
[albumin] / / [albumin]
/
car
/ [albumini [albumin]
An increased Ig index presumably indicates synthesis of the corresponding immunoglobulin.
intrathecal Oligoclonal
CLINICALCHEMISTRY, Vol. 34, No. 4, 1988
665
Table 1. Test Results for 13 PatIents wIth Symptomatic Neurosyphills and 75 Patients CNS Involvement SymptomatIc neurosyphills Test
TPR
n
Electrophoresis oligoclonal lg
8
12
Albuminratio ‘7.9
7
0.62 (0.32-0.86) 0.54
9
Total protein‘0.51 g/L
9 7
1gMindex 0.10
10 11
lgG index 0.70 and (or) 1gMindex ‘0.10 Cell count >5/4, and IgG index 0.70 and (or) 1gMindex 0.1O 95% confidence limitsin parentheses.
12
7
0.69
6
PV+, %
=
NP
where P = pretest probability of CNS involvement. Exact 95% confidence limits for each test characteristic were taken from scientific tables (7). To assess the significance of proportion differences between subgroups, we used the chi-square test for small samples (8). The 95% confidence limits of likelihood ratios were estimated by computer program (9). Results Table 1 shows the number of positive test results found in patients with neurosyphilis and in syphilitic patients without CNS involvement. Within both groups there was no significant difference between males and females. Influence of age on the test results is to be expected only for the albumin ratio and total protein content (10). Within the group of patients with neurosyphilis, albumin ratio and protein concentration was so marked that the influence of 666 CLINICALCHEMISTRY, Vol. 34, No. 4, 1988
8.7 (3.1-24.3) 20.2
0.97
1
1
+ (1 - P)ILR]
(2.8-19.9)
0.92
(4.2-97.2) 57.7
(0.91-.997)
0.92
immunoglobulins in CSF were demonstrated by electrophoon cellulose acetate (6). The upper limits of normal (97.5 percentile) for the protein content and albumin ratio were, respectively: 0.50 g/L and 7.8. For the cell counts and for the IgG and 1gM indexes, we used discrimination values that exceeded the accepted upper limits of normal, favoring specificity at the cost of sensitivity. We used the following cutoff values (upper limits of normal are given in parentheses): mononuclear cells: 5 per 4. (3 per 4.); IgG index: 0.70 (0.62); 1gM index: 0.10 (0.07). Statistics: True-positive rate (TPR) = sensitivity = the proportion of patients with symptomatic neurosyphilis who have a positive test result. True-negative rate CFNR) specificity = the proportion of patients with latent syphilis without CNS involvement who have a negative test result. Likelihood ratio (LR) of a positive test result = TPR/(1 TNR). We calculated the predictive value of a positive test result (PV+) according to Bayes’ theorem:
(0.82-0.96) 2
1
resis
0.91
5.8 (2.0-16.4) 7.4
0.91
(0.83-0.97)
0.85 (0.55-0.98)
0.62 (0.32-0.86)
(1.6-9.4)
(0.82-0.96)
0.99
(0.64-.998)
8
3.8
0.84
7
(0.25-0.81) 0.69 (0.39-0.91) 0.54 (0.25-0.81) 0.77
LR
(0.74-0.91)
(0.46-0.95)
lgG index 0.70
Syphilis without
ThR
(0.39-0.91)
Cell count>101,4.
Latent
Latsnt syphilis without CNS Involvsmsnt
n
Cell count >5/4.
with
(0.93-.999)
(7.4-451)
0.99 (0.93-.999) 0.99 (0.93-.999)
63.5 (8.2-492)
0
69.2
(9.0-532)
1.00
age could be neglected. The estimated test characteristics (TPR, TNR, and LR of positive test results) are given, with their 95% confidence limits. For each test the difference between the two groups of syphilitic patients was highly significant (P 5/4, and lgG Index 0.70 and (or) 1gMindex0.10
LR
1
5
3.8 5.8 7.4 8.7
4 6 7 8 17 37 39 41
17 23 28 31 52 75 77 78
10 30 39 45 49 69 87 88 88
100
100
100
20.2
57.7 63.5
69.2
because of negative treponemal CSF serology (1). As Table 1 shows, electrophoresis of CSF proteins yielded little information, with 16% of the syphilitic patients without CNS involvement showing oligoclonal Ig bands. The true-negative rate of this test was low (84%), and the true-positive rate was even lower (62%); thus the LR for a positive test result was 3.8. The albumin ratio will not give more information than the protein content. Using a higher discrimination value of 10 cells per 4. increased the estimated LR from 7.4 to 20.2. An increased IgO or 1gM index was found about 70 times more often in symptomatic neurosyphilis than in latent syphilis without CNS involvement. Although the likelihood ratios were estimated from a small data sample, we conclude that the traditional indicators for inflammation of CNS-a cell count of >5/4. and an increased protein content-change a pretest probability of CNS involvement from 5% into about 30% (Table 2). In contrast, a cell count of >10/4. gives a predictive value of about 50%, and an increased Ig index can change the pretest probability of 5% to 75%. Because no one in the group of syphilitic patients without CNS involvement had an increased IgG or 1gM index accompanied by a pleocytosis of more than 5 cells per microliter, the combination of positive results for these tests will give a very high likelihood ratio (LR -, see Table 1). Thus in the case of positive treponemal CSF serology, when other neurological conditions are improbable, such a finding is very suggestive for syphilitic CNS involvement even if the pretest probability is low. Such is the case in asymptomatic neurosyphilis. Low values, however, do not rule out this condition. In conclusion: although our reported ranges of the 95% confidence limits of the estimated test characteristics are
rather widespread, owing to small sample sizes, the IgG and 1gM indexes are valuable tests in the diagnosis of syphilitic CNS involvement. We thank Drs. J. van Manen, G. A. J. de Koning, D. Tio, T. M. Starink, and L J. Emsbroek for their helpful cooperation and Mrs. G. Lagerveld for her assistance at the outpatients department. References 1. Treponemal infection8. WHO Tech Rep Ser 1982;674:34. 2. Hiache EAR, van der Helm HJ, van Meegen MT, Blanken HIG. Protein estimation in cerebrospinal fluid with Coomassie Brilliant Blue [Letter]. Clin Chem 1982;28:1236. 3. Hiache EAR, van Meegen MT, van der Helm HJ. More precise determination of the cerebrospinal fluid IgG index [Letter]. Clin
Chem 1985;31:1417. 4. Hische EAH, van der Helm HJ, Out T. Estimation of 1gM in cerebrospinal fluid by fluoroimmunoassay. Clin Chim Acta 1979;97:93-5.
5. Link H, Wahren B, Norrby E. Pleocyto8is and immunoglobulin changes in cerebrospinal fluid and herpes virus serology in patients with Guillain-Barr#{233}syndrome. J Clin Microbiol 1979;9:305-16. 6. Van der Helm El, Hisehe EAR, van Walbeek HK. Monoclonal iinmunoglobulin demonstrable in cerebrospinal fluid by use of cellulose acetate electrophoresis [Letter]. Clin Chem 1980;26:19178.
7. Wissenschaftliche Tabellen Geigy, 8th ed. Basel: Ciba-Geigy, 1980: 89, 96. 8 Swinscow TDV, ed. The x2 tests. In: Statistics at square one. London: British Medical Association, 1982:49. 9. Albert A, Harris EK. Multivariate interpretation of clinical laboratory data. New York: Marcel Dekker, 1987:93-6. 10. Tibbling G, Link H, Ohman S. Principles of albumin and IgG analysis in neurological disorders. L Establishment of reference values. Scand J Clin Lab Invest 1977;37:385-90.
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