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Upper Limb Neuro

Myotonic Dystrophy

February 15th, 2021


  • Signs of Myotonic Dystrophy

  • Myopathic facies - temporalis wasting, mandibular wasting, frontal baldness
  • Flaccid dysarthria - nasal speech, breathiness, monotony, impaired articulation
  • Warm-up phenomenon - grip myotonia, repeated eye closure
  • Percussion myotonia - muscle contraction with percussion of the thenar eminence
  • Wasting of the forearm and small muscles of the hand
  • Distal muscle weakness
  • Hyporeflexia
  • Causes of Myotonia

  • Myotonic Dystrophy

  • Dystrophia myotonia
  • Myotonia congenita
  • Non-Dystrophic Myotonia

  • Paramyotonia congenita
  • Acid maltase deficiency
  • Manifestations of Myotonic Dystrophy

  • Myotonia
  • Cognitive impairment
  • Cataracts
  • Hearing impairment
  • Endocrine - diabetes, hypogonadism, secondary hyperparathyroidism
  • Cardiovascular - arrhythmia, cardiomyopathy, sudden cardiac death
  • Respiratory - obstructive sleep apnoea
  • Gastrointestinal - transaminase elevation, constipation / diarrhoea
  • Hypogammaglobulinaemia

Warm-Up Phenomenon

  • How to Assess

  • Grip myotonia - ask the patient to repeatedly grip and release your fingers, watching for initial muscle stiffness followed by relaxation with repeated performance
  • Repeated eye closure - ask the patient to repeatedly close and open their eyes, looking for initial lag followed by improvement with repetition.
  • Significance

  • Initial stiffness and lag that improves with repetition is a sign of myotonia.

Percussion Myotonia

  • How to Perform

  • Repeatedly percuss over the thenar eminence, looking for the development stiffness and potentially abduction of the thumb.
  • Significance

  • A sign of myotonia.
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