Pediatric, Rare Neurometabolic, and Paroxysmal Movement Disorders

Objective: To describe a novel manifestation of SCA27B in a patient whose presenting symptom was episodic, isolated truncal dystonia.Background: SCA27B is a late-onset hereditary ataxia that has been characterized thus far by pan-cerebellar symptoms including gait ataxia, appendicular ataxia, nystagmus, visual disturbances, postural tremor, and vertigo that can be episodic in nature and triggered by exertion [1-6].4-aminopyridines, such as dalfampridine, have been shown to improve the severity of ataxic symptoms in more than half of patients with SCA27B [1, 2,[4][5][6][7][8].Based on our literature review, there have been no previously documented cases of SCA27B manifesting with dystonia.Methods: Case report.Results: A 71-year-old male presented with two years of episodic, exercise-induced gait instability.Symptoms were triggered after walking at least one mile and resolved after 15 minutes of rest.Home videos demonstrated truncal dystonia involving approximately 20 degrees of lateral flexion causing gait impairment.Over time, his exercise tolerance decreased, with shorter intervals to symptom onset.In the office, neurological examination was normal; there were no abnormal movements or posturing while seated or walking.Over 2.5 years later, interictal exam revealed only trace dysmetria on finger chase test but was otherwise normal, including speech, eye movements, coordination, and gait.MRI of the brain showed subtle cerebellar vermian atrophy.MRI of the thoracic spine revealed only very mild multi-level spondylosis.Sequential trials of clonazepam, baclofen, and carbidopa-levodopa provided no symptomatic relief.Whole genome sequencing was performed which revealed one pathogenic expanded allele with 307 GAA repeats in the FGF14 gene, consistent with SCA27B.Following this, a trial of dalfampridine 10 mg twice daily was initiated.After approximately 2 weeks, the patient reported symptomatic improvement, demonstrated by increased exercise tolerance allowing him to walk longer distances prior to symptom onset.Conclusions: In this case, the initial and predominant manifestation of SCA27B was episodic, exercise-induced truncal dystonia, rather than cerebellar ataxia, expanding the previously understood phenotype of SCA27B.Symptoms are responsive to dalfampridine, consistent with previous reports of patients with SCA27B.