Nondystrophic Myotonic Disorders

Nondystrophic myotonias have prominent myotonia, well-developed muscles, and minimal weakness. Mobility improves with exercise. These channelopathies are transmitted as autosomal dominant or recessive traits. Electrophysiology confirms myotonia, and genetic tests are available to support the diagnosis. Membrane stabilizers reduce functional disability in most patients. Paramyotonia is less common, dominantly transmitted, worsens with cold and exercise, and affects the upper parts of the body.