[P300 and Parkinson disease. The role of cognitive changes]

Cognitive disturbances are frequently encountered in advancing Parkinson's disease (PD). Typically there are visuo-spatial disorders, memory impairment and bradyphrenia, defined as 'subcortical dementia' to distinguish it from the dementia that occurs in Alzheimer's disease, where the most prominent dysfunctions are agnosia, apraxia and aphasia. An electrophysiological test to study cognitive processing is the P300 (or P3) of the Event Related Potentials; in particular the latency of the P3 seems to correlate with cognitive decline. Thirty patients affected with idiopathic PD were investigated using a classic auditory "oddball" paradigm (rare tone--"target"--3000 Hz, frequent tone--"non target"--1000 Hz; the patients were instructed to recognize and keep a mental count of the number of rare tones). Electrophysiological findings were compared with those obtained in twenty normal subjects, age and sex matched with the patient's group. The parameters of P300 were correlated with patient's age, duration of the disease, motor and cognitive impairment levels and L-Dopa therapy. The P300 was loss in 16.6% (5 p.) and delayed in 33.3% (10 p.). Significative correlations were found only with age and cognitive impairment scores, but not with other variables analyzed. These results suggest that P300 could be a useful test to identify demented patients among those with PD, despite different motor disabilities.