Coexistence of tics and parkinsonism: evidence for non-dopaminergic mechanisms in tic pathogenesis.

We report four patients with tics since childhood who presented with typical Parkinson's disease (PD). No alteration in tics occurred before or during the development of symptoms. L-Dopa/carbidopa therapy in three patients improved parkinsonism without worsening tics over 3 months to 11 years of follow-up. Our experience fails to support hypotheses exclusively emphasizing overactivity of dopaminergic function underlying tics that would predict that PD would reduce and L-dopa exacerbate tics. This emphasizes the role of other neurotransmitter systems in the pathophysiology of tics.