Study of auditory brainstem responses in presbyacusis

0 downloads 0 Views 439KB Size Report
Presbyacusis is loss of hearing resulting from degenerative ... tone audiometery, also SISI and tone decay were ... statistically analysed using students 't' test.
STUDY OF AUDITORY BRAINSTEM RESPONSES IN PRESBYACUSIS R. S. Minhas, Senior Resident N. K. Mahindroo, Assistant Professor, C. Mohan, Associate Professor, M. L. Sharma, Prof. and Head, Department of ENT, IGMC, Shimla The results of auditory brainstem evoked responses in 25 subjects of presbyacusis are compared with 25 age and sex matched controls. Absolute latent periods of wave I through V were significantly prolonged in presbyacusis group. Delayed wave I and no significant change in interwave interval latencies of I-V, III-V and mild shortening of interwave interval of I-III in presbyacusis is observed. Key Words : Presbyacusis, Sensori-Neural Deafness, Latency. INTRODUCTION

Presbyacusis is loss of hearing resulting from degenerative changes of aging characterized by progressive high frequency hearing loss. Zwaardemaker 1was first to recognise on Pure Tone Audiometery that in presbyacusis there is impairment of hearing for high pitched sounds and it has been assumed to be sensori-neural in nature. ~ Schuknecht 2 while working on the histopathology of ears of cats and human with sensorineural deafness concluded two types of presbyacusis one epithelial atrophy-characterized by degenerative changes begining at basal end of cochlear duct and other neural atrophy characterized by degeneration or spiral ganglion cells begining at basal end and neurons of the higher auditory pathway whereas, Hinchcliffe (1962) maintained that degenerative changes in auditory mechanism were primarily attributable to central nervous system instead of lesion in the end organY Rosen4 in a study of the hearing of a noise free population in Africa emphasised the role of circulation, nutrition, heredity,, time changes, climate and the stress and strain of modern civilization which contribute to the time of onset and magnitude of presbyacusis. IJO & HNS Special Issue, 1997

Gacek and Schuknecht 5 described four varieties of presbyacusis namely-senory presbyacusis, neural presbyacusis, metabolic presbyacusis and mechanical presbyacusis. Sensory presbyacusis involves atrophy of organ of corti and the auditory nerve at the base of cochlea starting in middle age and progressing slowly. Neural presbyacusis results from loss of neurons in the auditory pathways and cochlea, metabolic presbyacusis due to atrophy of stria vascularis and mechanical presbyacusis due to disorder in the mechanics of cochlear duct. Jewett and Williston 7 introduced auditory evoked potential and helped in diangosis of various disorders of nervous pathways 6-7. MATERIAL AND METHODS

The present study was conducted in the department of E. N. T., I. G. Medical College, Shimla between 50-65yrs of age (group-II) 25 subjects of presbyacusis were evaluated and compared with 25 normal subjects of similar age group (group-I). A detailed history and complete E. N. T. exam was done in every patient to rule out any other middle/inner ear pathology, diabetes, hypertension, is-chaemic heart disease, renal disorder, tuberculosis, cerebrovascular disorder and were excluded from the study. Subjects with history of heavy smoking, on 53

Study of Auditory Brainstem Responses in Presbyacusis--R. S. Minhas et al. anticonvulsants, methyldopa, nitrofurantion, reserpine and other drugs which effect central nervous system functions were also not included in the study. Hearing assessmer~twas done by pure tone audiometery, also SISI and tone decay were performed to differentiate, cochlear and retrocochlear lesion. Brain stem evoked response audiometery was conducted on both the groups to localize the probable site of lesion in presbyacusis and to study the difference in latencies of waves in male and female in old age group in normal as compared to presbyacusis patients. N icolet compact IV 2000 system with invertive electrode placed at vertex and non invertive on mastoid process of both side was used to record brain stem auditory evoked responses (Fig.l). Stimulus was in the form of rarefaction clicks total 2000, 11.4/sec at 40 dB nhl above the threshold level with masking noise in non-test ear. The responses was amplified, averaged and displayed on a video display unit. The parameters used were absolute latencies of wave-I, III and V. Interpeak latencies of I-III, III-V and I-V were calculated. The results were

statistically analysed using students 't' test. RESULTS

The mean absolute latencies of individual waves of patientsJwere compared with normal group. (a) Wave h Absolute latent period in control group was 1.449 msec as compared to 2.45 msec in presbyacusis patient. The difference is statistically significant (P < 0.001). (b) Wave IIh Absolute latent period in control group was 2.949 + 0.19 msec and in patient it was 3.84+0.34 msec it was statistically significant (P < 0.001). (c) Wave V: Mean absolute latent period of wave V in control group was 4.35 +0.22 msec. In patient it was 5.33+0.33 sec it was statistically significant (P