[Case of DYT1 dystonia (early-onset torsion dystonia) showing long-term focal dystonia in the arm].

DYTI dystonia (DYT1-D, early-onset torsion dystonia) is caused by a GAG deletion in the DYTI gene. Here we report a girl with child-onset familial DYT1-D showing localized arm involvement. The patient developed postural and action dystonia in the right and left arms at 7 and 9 years, respectively. She was misdiagnosed as hysteria due to lack of abnormalities on laboratory tests. At 11 years of age she was introduced to our clinic. Increased muscle tonus and dystonic discharges seen on surface electromyogram in the right arm and the sternocleidomastoid muscle led to the diagnosis of dystonia. A GAG deletion in the DYTI gene was confirmed in the patient, her healthy father and paternal grandfather with torsion dystonia. Titration of levodopa resulted in the fluctuation of her arm dystonia. Combined therapy by levodopa and trihexyphenidyl relieved postural dystonia in the right arm but not action dystonia in the left. Both types of dystonia in the right and left arms were well ameliorated by the additional increase of levodopa. Somatosensory evoked potentials demonstrated abnormal premovement gating. The latency and accuracy of the amplitude were disturbed in visually guided saccadic eye movement. Now at more than 11 years after onset, the patient has not shown torsion or involvement of the lower extremities. Most DYT1-D patients are refractory to medication and early surgical intervention is recommended. However, the presence of DYT1-D patients showing a milder disease course should also be considered.