Writer's Cramp as the First Symptom of Spinocerebellar Ataxia 14
Authors: Roberto Erro MD, Carla Cordivari MD, Mark J. Edwards PhD, MRCP and Thomas Foltynie PhD, MRCP
Article first published online: 6 DEC 2014 | DOI: 10.1002/mdc3.12109
A 57-year-old right-handed man with no family history of neurological disorder presented with an 18-month history of abnormal posturing of his hand upon writing. Abnormal posturing did not affect any other activities, but was significantly disabling given that he had to write frequently as part of his work. Neurological examination was normal apart from abnormal posturing of his right hand upon writing, with hyperextension of the right thumb, with (possibly secondary compensatory) hyperflexion at the distal interphalangeal joint. He received partial benefit from botulinum toxin injections and was able to successfully manage his symptoms for the subsequent 8 years.
At the age of 65, he became aware of progressive balance difficulty. When walking, he started veering off to the left or to the right inconsistently. On examination, ocular movements were normal. There was a bilateral postural jerky tremor of his hands (right>left). Finger-nose and heel-shin tests were normal. He had rebound phenomenon in both upper limbs and minor difficulties when tandem walking (see Videos 1 and 2). The remaining neurological examination was normal. Brain MRI revealed mild atrophy of the cerebellum (Fig. 1). Genetic testing for the most common forms of SCAs was performed and he was found to carry a previously described mutation (c.413T>A, p.V138E) in PRKCG, leading to diagnosis of SCA14.
Figure 1. Sagittal T1-weighted MRI showing mild cerebellar atrophy.
We have reported here on a patient with a 10-year history of isolated writer's cramp before developing balance problems accompanied by cerebellar signs on examination and confirmed to carry a pathogenic SCA14 mutation. At first presentation, there were no clinical clues by history or examination to suggest cerebellar involvement. Clinically, our case had, in fact, a typical writer's cramp with evident mirroring, which is thought to be suggestive of primary dystonia, even though we might argue, in retrospect, that age at onset (i.e., 55 years) was outside the usual range of patients with isolated writer's cramp, who often develop their initial symptoms in their thirties.
SCA14 accounts for 2% of all SCAs and is caused by mutations of the PRKCG gene. SCA14 consists of slowly progressive ataxia, dysarthria, and nystagmus, with a wide range of age at onset.[1-4] The relatively benign phenotype and slow progression of SCA14 (as observed in our patient) clearly differentiate this from other types of SCAs resulting from polyglutamine expansions. Different types of dystonia (i.e., task-specific, focal, and segmental forms) have been reported in SCA14,[3, 4] yet never as the presenting or predominant clinical feature. Besides dystonia, additional features can be observed in SCA14, including myoclonus, tremor, and subtle cognitive impairment.[1-4] Although PRKCG is widely expressed in the central nervous system, neuropathological changes are limited to the cerebellum. It is therefore currently unknown how “extrapyramidal” symptoms, namely dystonia, develop in such patients.
Our case supports the variability in the clinical phenotype of SCA14 and might contribute to the ongoing debate of whether or not the cerebellum plays a role in dystonia.