Objective: To assess the presence and distribution of dystonia in spinocerebellar ataxia type 12 (SCA12).

Background: SCA12, commonly seen in the Agarwal community in India, is characterized by ataxia and tremor. While most of the studies on SCA12 discuss about tremor, there are few reports describing the dystonic presentations.

Method: 24 patients of SCA12 showing some form of dystonia were recruited for this study. Detailed examination was performed and the various movement disorders were noted with videography. Where required, surface electromyography (S-EMG) was done to characterize the tremor.

Results: Out of the 24 patients included in the study, 23 patients had upper limb dystonic posturing, mild to pronounced, predominantly distal, associated with the tremor. Indicators for dystonia included mirror and overflow dystonia, and the presence of a null point for tremor in some of the patients. Dystonic component was evident in several patients with rest tremor. Dystonia could be seen in the tremulous segment, or in a distant segment. 18 patients had cervical dystonia, ranging from mild posturing to significant dystonia. 3 patients had a focal cervical dystonia as the presenting symptom and developed ataxia at a later stage. 4 patients showed lingual dystonia, 2 had dystonia of the lower limbs, and 2 had truncal dystonia. Blepharospasm and laryngeal dystonia were present in 1 patient each. S-EMG of the upper limbs showed 3.5-5 Hz tremor with synchronous bursts of 100-250 ms duration.

Conclusion: Dystonia appears to be more frequently associated with SCA12 than previous estimates. It ranges from mild posturing of the tremulous limbs to distressing cervical dystonia. The electrophysiology is also compatible with a dystonic tremor. Further studies will be useful to understand the pathophysiology of dystonia in SCA12.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/a-study-on-the-phenomenological-analysis-of-spinocerebellar-ataxia-type-12-revealing-a-dystonic-imprint/