Skeletal Muscle Channelopathies

Abstract

Myotonia is involuntarily slowed relaxation after a forceful voluntary muscle contraction. Patients experience it as muscle stiffness. Electrical hyperexcitability of the muscle fiber membrane is the basis of myotonia, which is apparent in the form of repetitive action potentials on electromyography (EMG). The stiffness recedes with repeated contractions, a phenomenon called warm-up. Patients in whom muscle stiffness worsens with repetition or with cooling suffer from paradoxical myotonia, or paramyotonia. This type of myotonia is associated with episodes of flaccid limb muscle weakness resulting in the adynamia paramyotonia complex.