Psychiatric aspects of Parkinson’s disease

Typical consult question “Our patient is a fifty-eight year old man with Parkinson's disease. Lately, he seems uninterested and doesn't seem motivated to do anything anymore. Even when something good happens, he doesn't crack a smile. Is he depressed?” Background Overview of Parkinson's disease Parkinson's disease (PD) is a progressive neurodegenerative disease characterized by loss of dopaminergic neurons in the substantia nigra. Neurotransmission of serotonin, norepinephrine, and acetylcholine is also altered. The three principal motor symptoms of PD are rigidity, bradykinesia, and tremor. However, not all patients have all three motor symptoms. The classic tremor of PD is a rest tremor, but patients can have a postural or action tremor, or no tremor at all. Other early neurological signs include decreased facial expression (i.e., the masked face), or micrographia. Postural instability and autonomic dysfunction may occur later. About 1% of adults over age 60 have PD, with average age of onset in their sixties, although 5% to 10% of patients have young-onset PD, defined as onset before age 40. Although defined as a movement disorder, PD consists of overlapping motor, cognitive, and psychiatric features, which sometimes are difficult to distinguish. If a patient with PD has little emotional reactivity, is this the blunted affect of depression, an abulia characteristic of frontal-subcortical impairment, or the motor sign of facial masking? The frequency of psychiatric co-morbidities in PD and these phenomena of ambiguous origin often prompt psychiatric consultation.