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Case-of-the-month: autosomal recessive myotonia congenita: marked muscle weakness in a 16-year-old boy
1Department of Neurology, California Pacific Medical Center, San Francisco 94118.
Insights
This study details a 16-year-old boy with a decade of leg muscle stiffness and weakness. Findings suggest a potential link between exercise-induced electrical potential decline and myotonia symptoms.
Area of Science:
- Neurology
- Clinical Electrophysiology
- Muscle Physiology
Background:
- A 16-year-old male presented with a 10-year history of progressive leg muscle stiffness.
- Family history was negative for similar neuromuscular conditions.
Observation:
- Clinical examination revealed significant weakness in neck flexors, shoulder abductors, and ankle dorsiflexors.
- The patient exhibited generalized muscle hypertrophy, action myotonia, and percussion myotonia.
- Electromyography (EMG) showed reduced mean motor unit potential duration in the tibialis anterior muscle.
Findings:
- Muscle biopsy of the tibialis anterior revealed only minimal pathological changes.
- Repetitive nerve stimulation (30 Hz) and exercise of the tibialis anterior resulted in a decline of the compound muscle action potential.
- This electrophysiological decline correlated with the observed muscular weakness.
Implications:
- The findings suggest a possible exercise-induced electrophysiological abnormality contributing to myotonia.
- Further research into the mechanisms of myotonia and its electrophysiological correlates is warranted.
- This case highlights the utility of electrophysiological testing in diagnosing and understanding myotonic disorders.
Abstract:
A 16-year-old boy had a 10-year history of stiffness in leg muscles. There was marked weakness of neck flexors, shoulder abductors, and ankle dorsiflexors, with hypertrophy of most muscle groups and both action and percussion myotonia. The parents were normal. Motor unit potential mean duration was reduced in the weakest muscle (tibialis anterior), and a biopsy of the same muscle showed only minimal abnormalities. Exercise and repetitive stimulation (30 Hz) of the tibialis anterior disclosed a decline in the compound muscle action potential that appeared to correlate with the muscular weakness.