A Case of Paramyotonia Congenita

Abstract

The patient, a 15-year-old boy of normal intelligence, developed muscle stiffness in early childhood, with or without weakness, after physical exercises especially in the cold weather. This stiffness occurred in extremities, jaws, and the tongue, and was aggravated by physical exercises (paradoxical myotonia). Sometimes he experienced a generalized flaccid palsy immediately after violent exercises in the cold weather, but never at rest. The family history revealed 19 members with similar symptoms in 4 generations, and suggested the mode of autosomal dominant inheritance in this disease.
General physical examinations were negative. He was no neurological abnormality except for marked grip myotonia and eyelid myotonia. Slight percussion myotonia was elicited in the tongue and the deltoid muscle.
Laboratory examinations revealed elevated serum creatine phosphokinase (810 IU/I; normal range 0-150). Other laboratory data were all normal, including complete blood counts, blood chemistry, urinalysis, T3 and T4.
Administration of KCl (5g) resulted in an increase of plasma potassium concentration (from 3.5 to 4.5 mEq/l), and aggravation of the muscle stiffness and weakness was observed. EMG showed myotonic discharges on needle insertion and normal motor unit potentials at room temperature, but the muscle became contracted and electrically silent after the hand had been immersed in the water for 12 minutes.