Myotonic Dystrophy

Group of inherited conditions that show muscle weakness and myotonia (inability to relax after muscle contraction)

Aetiology

  • Classic dystrophia myotonica 1 (DM1) - AD mutation in dystrophia myotonica protein kinase gene DMPK
  • Type 2 myotonic dystophy (DM2) is a milder version caused by a different mutation (abnormally expanded section in ZNF9 gene)

Clinical presentation

  • Muscle wasting and weakness
  • Mournful facial expression (facial wasting, loose jaw)
  • Slurred speech (tongue/pharyngeal muscles involved)
  • Frontal baldness in males

Ocular manifestations

Common

  • Early onset cataract
    • Pathognomonic: stellate posterior cortical catact
    • Also 'Christmas Tree' (polychromatic) cataract (can also be age-related finding)
  • Ptosis
  • Hypermetrophia
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Stellate posterior cortical cataract
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'Christmas Tree' (polychromatic) cataract

Uncommon

  • Mild opthalmoplegia
  • Pupillary light-near dissociation
  • Pigmentary retinopathy
  • Optic atrophy