Objective: To describe a case of adult-onset, levodopa-responsive, paroxysmal dystonia.

Background: Adult-onset dystonia cases account for at least 90% of primary dystonia, however, less than 10% of those affect three or more body areas. In children and adolescents with generalized dystonia, a trial of levodopa is considered standard of care, though the phenotype of dopamine-responsive dystonia (DRD) is becoming increasingly diverse. Paroxysmal exercise-induced dyskinesia can share some clinical characteristics with DRD, including action-induced dystonia and levodopa response. Young-onset Parkinson’s disease should also be considered in cases with levodopa response.

Methods: We report a 51 year-old man with schizoaffective disorder that presented with abnormal involuntary movements, presumed to be a tardive syndrome. The symptom most concerning to the patient was 12-13 years of lower limb "cramping," initially induced by exercise. A typical episode began in the left leg, spreading to the contralateral leg and both arms, lasting 30-120 minutes. The “cramping” progressed to occur spontaneously several years later, with diurnal fluctuations. He also had a two-year history of resting and action hand tremor. His psychiatrist had noted facial “tics,” which she attempted to treat with fluphenazine. He had elected to discontinue all antipsychotic medications 10 months prior to this evaluation. Other than intermittent rest tremor, there were no signs of parkinsonism on examination. He was unable to induce a "cramping" episode in the office.

Results: Trials of lorazepam, baclofen, trihexyphenidyl, and fluphenazine were unsuccessful. Based on his history of paroxysmal dystonia and tremor, the patient was agreeable to a trial of levodopa. He reported improvement in “cramping” and tremor within four hours of taking the first dose. His response has been incomplete but functionally meaningful on 800mg of levodopa per day. GCH-1 gene sequence analysis is pending at the time of this submission.

Conclusions: This case represents an adult-onset, paroxysmal dystonia with partial levodopa response. While paroxysmal exercise-induced dystonia could be considered, adult-onset cases are very rare. It would also be unlikely for a case of young-onset Parkinson’s disease to not be clinically obvious 12 years after onset. It remains an area of debate if an incomplete response to levodopa can occur in DRD, which has provoked genetic testing in this case.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/an-atypical-case-of-adult-onset-levodopa-responsive-paroxysmal-dystonia/