Key result
Paramyotonia congenita associated with the SCN4A T1313M mutation can cause persistent distal hand weakness and muscle atrophy, with symptoms and electrophysiological decrements improving after acetazolamide administration.
Why the study?
Paramyotonia congenita typically presents with transient muscle stiffness, while interictal persistent muscle weakness is uncommon.
Case Report (n=3)
Paramyotonia congenita associated with the SCN4A T1313M mutation can cause persistent distal hand and cranial muscle weakness with myopathic changes, which may partially improve with acetazolamide.
Persistent weakness may occur in PC and alter management; extends SCN4A phenotypic spectrum but leaves confirmation to larger studies.
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.
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Taminato et al. (2019) conducted a case report in Paramyotonia congenita (n=3). Acetazolamide vs. Baseline (pre-treatment) was evaluated on Clinical symptoms and compound muscle action potential (CMAP) decrement. Paramyotonia congenita associated with the SCN4A T1313M mutation can cause persistent distal hand weakness and muscle atrophy, with symptoms and electrophysiological decrements improving after acetazolamide administration.
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