Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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September 5, 2024
Spinocerebellar Ataxia
- Background:
- The spinocerebellar ataxias (SCAs) are a group of autosomal dominant degenerative diseases characterized by cerebellar ataxia.
- Spinocerebellar ataxia type 7 (SCA7) is primarily a late-onset disorder. The pathology is characterized by gradual and progressive loss of motor coordination and vision due to retinal and cerebellar degeneration.
- SCA7 is caused by expansion of an unstable trinucleotide CAG repeat that encodes a polyglutamine tract in the corresponding protein, ataxin-7.
- The estimated prevalence is fewer than 1:300,000.
- Clinical Presentation:
- The defining feature of SCA7 is visual deterioration due to macular degeneration (pigmentary retinal dystrophy), leading to progressive and irreversible blindness.
- The first neurologic sign of SCA7 is typically gait ataxia. Limb ataxia develops over the following years. Invariably, dysarthria develops.
- Additional symptoms frequently include dysphagia, ophthalmoplegia, and pyramidal signs. Extrapyramidal signs are less common than pyramidal signs. Dementia and hearing loss are rare.
- Key Diagnostic Features:
- The most prominent radiographic finding is pontocerebellar atrophy, with greater involvement of the pons than in the other SCAs. Cerebellar atrophy correlates with disease progression.
- Atrophy can also be seen prominently within the remaining brainstem and cerebellar peduncles.
- Atrophy cerebral hemispheric white matter and also some cortical fields such as the parahippocampal gyrus, postcentral gyrus, precentral gyrus, cingulate gyrus, and the occipital corticies. The degree of cerebral atrophy is generally less severe compared with pontocerebellar atrophy.
- Differential Diagnosis:
- Multiple system atrophy cerebellar type (MSA-C): Also characterized atrophy of the cerebellum and brainstem, notably involving the middle cerebellar peduncle. Cruciform T2 hyperintensity in the pons (hot cross bun sign) is a well-described finding.
- Other spinocerebellar ataxias: Similar conditions invariably demonstrate cerebellar atrophy with or without brainstem involvement. Involvement of supratentorial white matter is also variable. Although there is significant overlap with finding in SCA7, retinal degeneration is characteristic to SCA7.
- Treatment:
- Without specific or curative therapies, treatment focuses on symptom management.
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