Computer mouse-related dystonia: a novel presentation of task-specific dystonia

Abstract

Task-specific dystonia (TSD) is a disabling movement disorder characterized by focal, involuntary, and excessive muscle contractions that develop in a single body part involved in highly skilled tasks [1]. In TSD, involvement of the hand (while writing, typing, or playing a musical instrument) is more common than the involvement of other parts of the body, but TSD related to the use of a computer mouse has never been described. A 68-year-old right-handed man presented to our outpatient clinic with involuntary flexion of his right thumb, which interfered with the use of a computer mouse. When the patient was 62 years old, he started composing music using a computer. Since then, he had used the computer mouse with his right hand for composition for approximately 5 h per day. At age 64, he developed abnormal flexion of his right thumb whenever he used the computer mouse; the flexion interfered with moving the mouse, but he could click the mouse button without any trouble. During the following year, abnormal flexion in the right thumb was observed even when the patient put his right hand on the table, and he had difficulty in extending and flexing his right thumb voluntarily. This forced him to use the computer mouse with his left hand instead. He had no symptoms in other parts of the body. The patient had played classical guitar since childhood. He had no previous medical history of psychiatric disease or a family history of dystonia. The patient had no history of alcohol use or smoking. The initial examination showed excessive flexion of his right thumb, and voluntary flexion and extension of his right thumb was impaired. This abnormal posture significantly worsened when using the computer mouse (see video, segment 1). However, he noticed that right-thumb flexion never occurred while eating (using chopsticks, spoon, or knife) or writing with a pen. The abnormal flexion of his right thumb never occurred when his right thumb and index finger touched. A neurological examination was unremarkable except for the abnormal flexion position of his right thumb. Laboratory data were normal. The finding of brain magnetic resonance images was normal. TSD was diagnosed based on the observation that involuntary and excessive flexion posture was prominent in specific situations. Oral medications such as levodopa, carbamazepine, and phenytoin were ineffective. The patient was then treated with clonazepam 0.5 mg, which modestly improved his symptoms. The combined use of clonazepam 1 mg and trihexyphenidyl 6 mg resulted in significant improvement of his symptoms (see video, segment 2). We report the first case of a patient in whom excessive flexion of the right thumb occurred initially only when using the computer mouse. Similar to other TSD patients [1], our patient’s symptoms later involved other tasks. As the patient had dystonic posturing of the right hand at rest at the examination, the patient was classified as having complex TSD rather than simple TSD [2]. His finger movements were preserved when his right thumb and index Electronic supplementary material The online version of this article (doi:10.1007/s00415-012-6519-1) contains supplementary material, which is available to authorized users.