A Case of Paramyotonia Congenita

ABSTRACT

Paramyotonia congenita (PMC), an autosomal dominant non-progressive muscle disorder, is characterised by cold-induced stiffness followed by muscle weakness. The weakness is considered to be caused by a dysfunction of the sodium channel in muscle fiber. We report a 37-year-old male patient with PMC, complaining of episodic myotonia and motor weakness on cold exposure. In this patient, we performed clinical and neurological examination, electrophysiologic examination and muscle biopsy. On electrophysiologic study, needle EMG showed spontaneous myotonic discharges at room temperature but disappeared after cooling. Amplitude of compound action potential in abductor pollicis brevis muscle decreased significantly after cooling the tested extremity. Muscle biopsy showed a minimal variation of muscle fiber diameters, internal nuclei, chained nuclei, occasional atrophic fibers in vastus lateralis muscle. His mother, his son, three of six siblings, and five of eleven nephewes are affected with same symptomes.