Abstract
Evoked brainstem responses (ABR) to 75 dB nHL condensation (C), rarefaction (R), and alternating (A = C + R) clicks were investigated in healthy subjects and in patients with multiple sclerosis. A new wave IV—V ‘shape ratio’ (SRIV—V) was most sensitive. SRIV—V correlated most strongly with clinical MS classification, and seemed to be rather specific for retrocochlear dysfunction. Wave IV—V amplitude was also more sensitive than the common IV—V amplitude ratio. The variability of latencies and interpeak latencies was lower in ABR to A clicks than in ABR to either R or to C clicks. In patients, fewer subcomponents were found in ABR to A than in ABR to R and C clicks. ABR to A clicks were on the average slightly more sensitive than either C or R click ABR. Our results suggest that both A-mode ABR and the ‘dispersion’ variable SRIV—V can be used without significant problems in the diagnosis of brainstem demyelination. A test protocol which requires ABR to both C and R clicks to be abnormal, will, however, be less sensitive, though probably more specific.