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myotonia
Delayed relaxation of a muscle after an initial contraction.
Etiology:
1) myotonia congenita
2) myotonic dystrophy (myotonia dystrophica)
3) chondrodystrophic myotonia
4) paramyotonia congenica
5) hyperkalemic periodic paralysis
6) Schwartz-Jampel syndrome
Pathology:
- sustained muscle tensing that prevents muscles from relaxing normally
- impairment of muscle relaxation is due to increased membrane excitability
Clinical manifestations:
1) generally painless
2) muscle stiffness that can interfere with movement
3) in some people the stiffness is very mild, while in others it may be severe enough to interfere with walking, running, & other activities of daily life
4) may interfere with fine hand movements
Laboratory:
- EMG shows myotonic discharges with insertional activity
Management:
1) quinine
2) phenytoin
3) mexiletine
Related
electromyography (EMG)
General
musculoskeletal sign/symptom
myotonic disorder
References
- Harrison's Principles of Internal Medicine, 13th ed.
Isselbacher et al (eds), McGraw-Hill Inc. NY,
1994, pg 131
- Electrodiagnosis in Diseases of Nerve and Muscle, Principles
and Practice, Kimura, J. FA Davis, Philadelphia, 1983
- Medical Knowledge Self Assessment Program (MKSAP) 17,
American College of Physicians, Philadelphia 2015