Role of middle latency auditory evoked potentials in parkinsonism: An electrophysiological clue

Introduction: Middle latency auditory evoked potentials (MLAEPs) allow the assessment of the function of the central part of the auditory pathway. MLAEP abnormalities have been demonstrated in patients with Alzheimer’s and Parkinson’s disease with dementia. Objective: The objective of our study was to assess the MLAEP findings in patients with idiopathic Parkinson’s disease (IPD) and atypical parkinsonism (AP) and to determine whether MLAEPs could contribute to the differential diagnosis of IPD and AP. Methods: We included 75 participants (25 IPD patients, 25 AP, and 25 age-matched healthy control subjects). MLAEPs were recorded in all patients and control subjects as per the standard procedure for MLAEP recordings. Absent waveforms (Na and Pa waves) and prolonged latencies of individual waves were considered as abnormal MLAEP readings. Results: The Pb waveform was significantly absent in the patients with IPD and AP compared to control subjects (p = 0.02). The Pb waveform was significantly absent in the AP group compared to the IPD group (p = 0.03). The Pb waveform was significantly absent in the AP group without cognitive impairment compared to the IPD group without cognitive impairment (p = 0.003). There was no statistically significant difference between the patients with IPD with and without cognitive impairment (p = 0.07). There was no significant difference among the groups with respect to Na and Pa wave latencies. Other parameters such as Na–Pa amplitude and Nb–Pb amplitudes were not significant among the groups. Conclusion: The absence of Pb potential in AP is an electrophysiological clue for the diagnosis of AP in patients presenting with parkinsonism. MLAEPs can act as an electrophysiological adjunct to the clinical imaging markers in differentiating IPD from AP.