Why are some Parkinson disease patients unaware of their dyskinesias?

OBJECTIVE: To test the hypothesis that anosognosia for dyskinesias in Parkinson disease (PD) results from a failure to detect discrepancies between intended and actual movement.
BACKGROUND: PD patients often complain of drug-induced dyskinesias (involuntary movements) less than their carers. This remarkable unawareness is an example of anosognosia (ie, unawareness of deficits associated with an illness). A better understanding of anosognosia for dyskinesias in PD is important to understand the impact of the illness and side effects of treatment.
METHODS: The ability to detect a discrepancy between intended movement and visual feedback about actual movement was investigated in 6 PD patients with anosognosia for dyskinesias, 11 nonanosognosic PD controls with dyskinesias, and 22 healthy volunteers, using a mirror to reverse the expected visual consequences of an executed movement.
RESULTS: Nonanosognosic PD patients and healthy volunteers rated mirror-reversed movement as significantly stranger than normal movement (P=0.024 and <0.001, respectively), whereas PD patients with anosognosia for dyskinesias did not (P=0.375).
CONCLUSIONS: The findings support our proposal, in that PD patients with anosognosia for dyskinesias do not report mirror-reversed movement (in which intentions and visual feedback conflict) as feeling distinct from normal movement.