Myotonic Dystrophy

Muscular dystrophy (MD) refers to a group of nine genetic diseases that cause progressive weakness and degeneration of muscles used during voluntary movement; myotonic dystrophy is the most common form seen in adults

Aetiology

  • Autosomal dominant - two different triple repeat mutations
  • Patients usually present in their 20s

Clinical presentation

  • Myotonia - continued, involuntary muscle contraction after cessation of voluntary effort (failure of relaxation)
  • Features in the face: frontal balding, myopathic facies (a long and thin face), bilateral ptosis, cataracts
  • Features in speech: dysarthria (caused by a myotonic tongue and pharyngeal muscles)
  • Features in the neck: wasted sternocleidomastoid muscles
  • Features in the hands: distal wasting and weakness, slow relaxing grip, percussion myotonia (thumb flexion on percussion of the thenar eminence)
  • Internal features: insulin resistance/metabolic syndrome, cardiomyopathy/arrhythmia, testicular atrophy

Investigations

  • Raised CK
  • EMG
  • Muscle biopsy
  • Genetic testing

Management

  • Symptom management