 [ Symptoms ] how does parkinson is disease affect longevity and mental clarity [ Disease ] pd is typically a 20 year illness but can range from 10   40 years there are 2 basic subcategories tremor dominant and postural instabilitygait disturbance pigd the tremor dominant is much less likely to have memory problems and has a better prognosis in my experience   disability from work which i define as needing 12 hours to do an 8 hour work day   is seen on an average of 12 years after diagnosis advanced may affect thinking most of the time the cognitive changes have to do with speed of thinking   just like the motor changes have to do with the speed of moving think of it as a road that can only handle a certain amount of traffic if it is crowded with thoughts a person will have some trouble with word finding   or juggling all of the information this sometimes concerns family members and patients because they appear to not be remembering things in reality they did not move the information down the road to a memory circuit did not learn if you will so remember to take things more slowly 