Progression of Dysphagia in Spinocerebellar Ataxia Type 6

Spinocerebellar ataxia type 6 (SCA6), an autosomal dominant triplet repeat disease, predominantly affects the cerebellum with a late onset and generally good prognosis. Dysphagia is commonly associated with the outcomes of neurodegenerative diseases such as SCA6. Although the characteristics of dysphagia have been rarely reported in SCA6, our previous study indicated that dysphagia is generally milder in SCA6 than in SCA3, another inherited ataxia with multisystem involvement. However, abnormalities in the pharyngeal phase in SCA6 were indistinguishable from those in SCA3, with no explainable reason. To determine the reason, we repeatedly performed videofluoroscopic examinations (VF) in 14 patients with SCA6. The results showed that the gross progression of dysphagia was apparently slow, but four patients had progressive dysphagia at an early disease stage; dysphagia began within 10 years from the onset of ataxia and rapidly progressed. A common clinical feature of the four patients was a significantly older age at the onset of ataxia (74.0 vs. 60.3 years), associated with significantly shorter triplet repeats. This finding surprisingly indicated that patients who had shorter repeats and thereby later onset and potentially better prognoses were at risk for dysphagia-associated problems. Ischemic changes, homozygous mutation, and diabetes mellitus as well as aging might have contributed to the observed progressive dysphagia. We found that conventionally monitored somatosensory evoked potentials at least partly reflected progressive dysphagia. Despite the small study group, our findings suggest that clinicians should carefully monitor dysphagia in patients with SCA6 who are older at disease onset (>60 years).