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Spinoerebellar Ataxia (SCA)

Summary

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  • Progressive neurodegenerative disorder affecting the cerebellum and spinal cord
  • Characterised by ataxia, dysarthria, and oculomotor abnormalities
  • Imaging reveals cerebellar atrophy, with variable involvement of brainstem and spinal cord

Pathophysiology

  • Autosomal dominant inheritance in most cases
  • Caused by expansion of CAG trinucleotide repeats in various genes
  • Results in progressive loss of Purkinje cells and other neurons in the cerebellum and brainstem
  • Different SCA subtypes (SCA1-SCA48) with distinct genetic mutations and clinical features

Demographics

  • Prevalence: 1-5 per 100,000 worldwide
  • Onset typically in adulthood, but can occur in childhood or late adulthood
  • SCA3 (Machado-Joseph disease) is the most common subtype globally
  • Geographical variations in subtype prevalence exist

Diagnosis

  • Clinical presentation:
    • Progressive ataxia
    • Dysarthria
    • Oculomotor abnormalities (nystagmus, slow saccades)
    • Additional features vary by subtype (e.g., cognitive impairment, peripheral neuropathy)
  • Genetic testing to identify specific SCA subtype
  • Family history assessment
  • Neurological examination
  • Imaging studies to support diagnosis and exclude other causes

Imaging

  • MRI is the modality of choice
  • Key findings:
    • Cerebellar atrophy, particularly of the vermis
    • Pontine atrophy in some subtypes (e.g., SCA1, SCA2)
    • Spinal cord atrophy, especially in SCA1 and SCA3
    • T2/FLAIR hyperintensities in cerebellar white matter and middle cerebellar peduncles
  • Advanced techniques:
    • Diffusion tensor imaging (DTI) may show reduced fractional anisotropy in cerebellar white matter
    • Voxel-based morphometry can quantify regional brain volume loss

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  • A 35-year-old patient presented with progressive ataxia.
  • MRI showed severe symmetrical atrophy of the cerebellar hemispheres and vermis.
  • The ataxia genetic panel was negative (whole genome sequencing results are awaited).

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  • A 40-year-old patient presented with slowly progressive ataxia.
  • MRI showed severe cerebellar hemisphere, vermis, pontine atrophy.
  • Atrophy of the cervical cord was less pronounced.

Treatment

  • No curative treatment available
  • Management focuses on symptomatic relief and supportive care:
    • Physical therapy to improve balance and coordination
    • Occupational therapy for activities of daily living
    • Speech therapy for dysarthria
    • Medications for specific symptoms (e.g., baclofen for spasticity)
  • Genetic counselling for affected individuals and family members
  • Emerging therapies:
    • Antisense oligonucleotides to reduce mutant protein expression
    • Stem cell therapy (experimental)
    • Gene therapy approaches under investigation

Differential diagnosis

Differential Diagnosis Distinguishing Feature
Multiple System Atrophy (MSA-C) "Hot cross bun" sign in pons on T2; putaminal rim sign; more diffuse olivopontocerebellar atrophy including inferior olives
Friedreich's Ataxia Spinal cord atrophy with dorsal column T2 signal; relatively preserved pons; no middle cerebellar peduncle involvement
Paraneoplastic cerebellar degeneration Cerebellar cortical atrophy with FDG-PET hypometabolism; may show early FLAIR signal in cerebellum before structural atrophy
Fragile X-associated Tremor/Ataxia Syndrome (FXTAS) Symmetric T2 hyperintensity in middle cerebellar peduncles; cerebellar and cerebral white matter changes
CANVAS Syndrome Cerebellar cortical atrophy with preserved brainstem volume; dorsal column spinal cord involvement