Clinical Reasoning: Juvenile-Onset Dopa-Responsive Dystonia-Until It Isn't.

Dopa-responsive dystonia (DRD) encompasses a broad spectrum of phenotypically diverse conditions, offering unique diagnostic challenges. We describe the case of a 24-year-old woman with dystonic gait and jerky position-sensitive limb tremor that initially responded exquisitely well to low-dose levodopa, suggesting DRD. Two years later, she developed parkinsonian features, ultimately leading to a diagnostic reclassification. Despite extensive investigations, the underlying etiology remained elusive until 10 years after symptom onset. We discuss this DRD mimic and briefly review the disorders from which it must be distinguished.