Genetic Extraocular Myopathies

    • Disorder of extraocular muscles caused by mitochondrial or nuclear DNA abnormalities
    • Common causes: chronic progressive external ophthalmoplegia (CPEO), Kearns–Sayre syndrome (KSS), oculopharyngeal dystrophy (OPD), myotonic dystrophy (MD)
    • Uncommon causes: mitochondrial neurogastrointestinal encephalomyopathy syndrome (MNGIE)
    • Core clinical features
      • Symmetrically reduced and slow binocular eye movements
      • Often no diplopia because ductional deficits are equal in the two eyes
    • Possible accompanying clinical features
      • Ptosis
      • Convergence weakness
      • Pigmentary retinopathy, often asymptomatic
      • Iridescent or stellate cataracts (in myotonic dystrophy)
      • Swallowing difficulty
      • Generalized skeletal muscle weakness
      • Cardiac conduction defects
    • Imaging features
      • Thin (atrophic) extraocular muscles
    • Progressive supranuclear palsy
    • Chronic inflammatory demyelinating polyradiculoneuropathy
    • Fisher variant of Guillain–Barré syndrome
    • Myasthenia gravis
    • Spinocerebellar ataxia
    • Look for signs that suggest mimickers of extraocular myopathy
      • Intact vestibulo-ocular reflex suggests progressive supranuclear palsy
      • Numbness and absent deep tendon reflexes suggest chronic inflammatory demyelinating polyradiculoneuropathy or Fisher variant of Guillain-Barré syndrome
      • Weakness of orbicularis oculi, neck flexion, proximal limbs; difficulty breathing, eating, or swallowing suggest myasthenia gravis
      • Ataxia and nystagmus suggest spinocerebellar ataxia
    • Perform muscle biopsy for DNA analysis, electroretinography for pigmentary retinopathy, electrocardiography for cardiac conduction defects, swallowing study for esophageal dysmotility
    • Provide genetic counseling if a genetic extraocular myopathy diagnosis is confirmed
    • Trap: sudden death from cardiac arrhythmia and pneumonia from aspiration are major concerns in genetic extraocular myopathies
    • Depends on the underlying condition

    Extraocular Muscle Disorders

    Genetic Extraocular Myopathies Orbital Myositis Graves Disease Myasthenia Gravis