Myotonic myopathy with painful muscle contractions and decrease of symptoms by cold

Myotonic reaction and paresis accompanied by painful muscle contractions limited to the upper limbs, which decrease remarkably in the cold, were observed in a 29 year old man. The histological investigation revealed minimal non-specific signs of myopathy. The biochemical studies of muscular tissue contained a normal amount of myophosphorylase, acid maltase and glycogen. Ischemic work induced normal elevation of venous lactate. The activities of CPK, LDH and SGOT in the blood serum were occasionally increased. The EMG showed typical myotonic bursts and electrical silence during painful muscle contractions. Repetitive high frequency stimulation demonstrated a clear initial increase of the amplitude of action potentials followed by a decrease in the contracted muscle. The father of the patient suffered from dystrophia myotonica. This coincidnece suggests that this myotonic myopathy is a variant of dystrophia myotonica.