Myotonic disorders

Signs & symptoms: Diseases characterized by MYOTONIA, which may be inherited or acquired. Myotonia may be restricted to certain muscles (e.g., intrinsic hand muscles) or occur as a generalized condition. These disorders may be associated with abnormal muscle SODIUM CHANNEL and CHLORIDE CHANNELS. MYOTONIC DYSTROPHY and MYOTONIA CONGENITA represent two relatively common forms of this disorder. Proximal myotonic myopathy often presents with myotonia and muscle pain in early adulthood and later in life thigh muscle weakness and cataracts develop. Patients with myotonia may report painless muscle stiffness immediately upon initiating muscle activity after a period of rest (eg: inability to release hand grip after a strong handshake or trouble climbing stairs after a period of sitting). Lag in opening the eyes after initial tight eyelid closure. Myotonia improves with muscle exercise or repeated efforts, the so-called "warm-up phenomenon".