Paramyotonia congenita with persistent distal and facial muscle weakness: A case report with literature review

Introduction: Paramyotonia congenita (PC; OMIM 168300) is a non-dystrophic myotonia caused by mutations in the SCN4A gene. Transient muscle stiffness, usually induced by exposure to cold and aggravated by exercise, is the predominant clinical symptom, and interictal persistent weakness is uncommon. Case presentation: We report a family with a history of PC accompanied by persistent distal hand dominant muscle weakness with masticatory muscle involvement. Persistent weakness was exacerbated with age, and MR analysis showed marked atrophy of temporal, masseter, and finger flexor muscles with fatty replacement. Cases within the family harbor the prevalent PC causative mutation, T1313M, in the SCN4A gene. Administration of acetazolamide chloride improved clinical symptoms and the results of cold and short exercise tests. Phenotypic variation within the family was remarkable, as the two younger affected patients did not present with persistent weakness or muscle atrophy. Conclusions: PC associated with the T1313M mutation is a possible cause of persistent distal hand weakness.