Nonlinear decline of mini-mental state examination in Parkinson's disease.

The trajectory of cognitive functioning in patients with Parkinson's disease (PD) is not known. We used a random change point model to study the individual cognitive trajectory for up to 15 years in a prevalence sample of 238 PD patients, and used the mini-mental state examination (MMSE) to assess the longitudinal cognitive course. We observed that the rate of global cognitive decline was nonlinear. Following a relatively stable period, an inflection point was identified, after which the rate of decline gained momentum with an annual decline of 2.8 points on the MMSE. The course was similar in men and women. This inflection point was estimated to occur 13.3 years (95% credible interval 11.8, 13.6) after the diagnosis of PD; however, there were wide interindividual variations in the time from onset of PD to the inflection point.