Overview
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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