Myotonia

Myotonia is the group of neural muscular disorders, the main characteristic of which is the change of the muscle tone. Myotonia (Greek μυος — muscle and τόνος  — tone) or Thomsen disease is a rare hereditary disease characterized by long uncontrolled contractures of muscles after initially voluntary movements. In these patients the process of relaxation of the muscle fibers after contraction is disordered. The disease is not completely studied. The typical symptoms are the inability to relax a voluntarily strained muscle for several tens of seconds. However, in some cases of undoubtful myotonia the microscopic examination shows no changes in the muscular tissue. The manifestations are first observed in late childhood. The patient releases the spasm by the repeated voluntary contractions of the muscles. The myotonic phenomena exacerbate in cold and can significantly limit the movements. The contractures in the legs interfere with normal walking. The muscles look hypertrophic so that the patients look like athletes. Metabolic process is disordered, significant deviations from normal levels in the urine have been detected, but no regular myotonia-specific changes have been detected as these deviations are different in different cases.

Currently, the sodium channels blocker, Mexiletine is prescribed to relieve the muscle hypertonus. The efficiency of Mexiletine has been confirmed in the controlled trial, one of the few for orphan diseases. Such drugs as Phenytoin, Acetazolamide, Quinine also bring some relief. The clinical observations promise amelioration and sometimes almost complete cure. The myotonic signs reduce with age. The prognosis for life is favorable.