Myotonia is a symptom of a small handful of certain neuromuscular disorders characterized by delayed relaxation (prolonged contraction) of the skeletal muscles after voluntary contraction or electrical stimulation, and the muscle shows an abnormal EMG. Myotonia is the defining symptom of many channelopathies (diseases of ion channel transport) such as myotonia congenita, paramyotonia congenita and myotonic dystrophy. Brody disease (a disease of ion pump transport) has symptoms similar to myotonia congenita, however, the delayed muscle relaxation is pseudo-myotonia as the EMG is normal...