Auditory brainstem and middle latency evoked responses in the clinical evaluation of diabetes

The measurement of auditory brainstem evoked responses and middle latency evoked responses may improve the evaluation of diabetic neuropathy. Twenty diabetic patients were studied (12 males, 8 females), aged 21 to 63 years with normal hearing, together with 20 age- and sex-matched normal subjects (10 males, 10 females). Auditory brainstem evoked responses were induced by rarefaction clicks of 0.1 ms at a repetition rate of 21.1 CPS and an intensity of 75 dB hearing level. Middle latency evoked responses were induced with clicks of 0.1 ms, a repetition rate of 7.7 CPS and an intensity of 75 dB hearing level. Diagnostic criteria were: a I-V interval latency shift greater than 2SD of the control group for the auditory brainstem evoked response test or the interval difference of wave V greater than 0.2 ms. Middle latency evoked response was diagnostic if the latency of the Pa component was greater than 2SD of normals. Twenty-five per cent of subjects had retrocochlear impairment (absence of I wave) even in the absence of symptoms. The combined technique of auditory brainstem evoked response and middle latency evoked response improved the detection rate of central nervous system dysfunction. Auditory brainstem response is important for detecting desynchronization of the auditory response, whereas middle latency evoked response detects abnormalities in the more rostral regions of the central nervous system. In conclusion, there is a role for auditory brainstem evoked response and middle latency evoked response in the global assessment of diabetic neuropathy.