BCHE and Parkinson disease: A total of 2 large, randomized controlled cholinesterase inhibitor (ChEI) studies in Parkinson's disease dementia (PDD) have been published, 1 positive study for rivastigmine and the other an equivocal study for donepezil.2, 14 Although statistically significant, the effects of ChEIs in PD are clinically modest.133 Although rivastigmine is “clinically useful” for the treatment of PDD, the other ChEIs are “possibly useful.” ChEI treatment appears to be overall well tolerated in PD, outside of nausea and worsening tremor in some patients.