Task specific focal dystonia: a presentation of spinocerebellar ataxia type 6

Autosomal dominant cerebellar ataxias (ADCA) are characterised by clinical and genetic heterogeneity with a substantial overlap of clinical features and a variable degree of adherence to three distinct phenotypes according to Harding’s clinical classification: ADCA type I, II, and III.1 The availability of molecular genetic testing has provided increasing appreciation of a wider clinical spectrum than previously thought for each ADCA subgroup. In addition there is an increasing list of genes harbouring disease causing mutations which, to date, include spinocerebellar ataxia (SCA) types 1, 2, 3, 6, 7, 8, 10, 12, and 17.2 SCA 6 is caused by unstable CAG expansion in the α-1A calcium channel gene (CACNA1A).4 We present a confirmed case of SCA 6 presenting with a task specific focal dystonia (writer’s cramp) predated the onset of progressive gait ataxia by five years, which further widens the clinical spectrum of SCA 6. A 57 year old female pharmacist first presented at the age of 42 with a two month history of progressive difficulty in writing prescriptions as a result of writing induced cramp affecting the right hand. This task specific focal dystonia was aggravated by stress and fatigue. Her father was reported to have had Parkinson’s disease on the basis of developing tremor and gait disturbance at age 40. On examination, the patient’s gait was normal and no focal neurological deficits were …