ABSTRACT
Dopa-responsive dystonia (DRD) is characterized by lower limb-onset, diurnally fluctuating dystonia and dramatic and sustained response to levodopa treatment. Segawa disease, an autosomal dominant deficiency of guanosine triphosphate cyclohydrolase 1 (encoded by GCH1) is the most common and well-known condition manifesting as DRD. However, similar clinical manifestations can be seen in individuals with deficiencies of other enzymes that are involved in the biosynthesis of dopamine. We describe the case of an 11-year-old girl who presented with abnormal gait, which had initially begun 2 years back. The patient showed diurnally fluctuating dystonia in both legs. She was able to walk without support in the morning, but was unable to stand without support in the evening. She had been diagnosed as having spastic cerebral palsy and had been managed with physical therapy at a local rehabilitation clinic. The patient had been healthy until the development of dystonia, and did not have a history of perinatal problems or developmental delay. Routine hematologic and biochemical test results were normal. Brain magnetic resonance imaging and electroencephalography showed no abnormalities. When levodopa was administered, the patient's abnormal gait dramatically improved 1 hour after receiving the medication. Genetic testing for the GCH1 gene revealed a missense mutation (c.293C>T [p.A98V]) that has previously been reported in patients with DRD. This case demonstrated that a levodopa trial is vital for accurate and early diagnosis of DRD in patients with dystonia resulting from an unknown cause.