Middle latency auditory evoked potentials in patients with parkinsonism

The aim of this study was to assess the middle latency auditory evoked potential (MLAEP) findings in idiopathic Parkinson's disease (IPD) and in patients who are regarded as having atypical parkinsonian disorders (AP) and to determine whether MLAEPs could contribute to the differential diagnosis of IPD and AP.MLAEPs were evaluated in 19 control subjects and in a total of 35 patients with parkinsonism, of which 27 had IPD and 8 had AP. Among IPD patients, P1 was absent in 1 nondemented patient with young-onset Parkinson's disease (YOPD) (5%) and in 2 of 7 demented (28.5%) IPD patients. In the AP group, 3 of the 7 (42.8%) nondemented patients and the one patient with dementia showed the absence of P1. The absence of P1 was found to be significantly higher in AP patients than IPD patients (p=0.0335).In conclusion, MLAEPs were found to be normal in nondemented IPD patients with only a few exceptions. The absence of P1 in nondemented patients with parkinsonian symptoms may bring the diagnosis of IPD into question. The absence of P1 could be detected in AP patients at least as often as in demented IPD patients. Thus, the measurement of MLAEPs may be a clinically useful adjunct to the clinical examination of patients with parkinsonism.