title: Asymptomatic myotonia congenita unmasked by severe hypothyroidism.
abstract: Myotonia congenita is an inherited muscle disorder sustained by mutations in the skeletal muscle chloride channel gene CLCN1. Symptoms vary from mild to severe and generalized myotonia and worsen with cold, stressful events and hormonal fluctuations. Here we report the case of a young woman who sought medical attention because of subacute onset of diffuse and severe limb myotonia. CLCN1 gene sequencing showed a heterozygous transversion (T550M), two polymorphisms and one silent mutation. Thyroid function screening revealed severe hypothyroidism. She was placed on l-thyroxine replacement therapy which dramatically improved myotonia. We conclude that hypothyroidism unmasked a genetically determined, clinically asymptomatic chloride channelopathy. Diagnostic work-up in patients with clinically isolated myotonia should not be limited to genetic screening of non-dystrophic or dystrophic myotonias. Considering the high prevalence of hypothyroidism in females, systematic thyroid function screening by looking for additional hypothyroid symptoms and serum TSH levels measurement is mandatory in these patients.
authors: Endocrinology and Diabetology Unit, Dept. Biomedical Sciences for Health, University of Milan, IRCCS Policlinico San Donato, San Donato M.se, Milan, Italy.
authors: Elena
authors: E
authors: Passeri
authors: NEuroMuscular Omnicentre (NEMO), Fondazione Serena Onlus, Dept. Biomedical Sciences for Health, University of Milan, Milan, Italy.
authors: Valeria A
authors: VA
authors: Sansone
authors: Molecular Biology Laboratory, IRCCS Policlinico San Donato, San Donato M.se, Milan, Italy.
authors: Chiara
authors: C
authors: Verdelli
authors: Endocrinology and Diabetology Unit, Dept. Biomedical Sciences for Health, University of Milan, IRCCS Policlinico San Donato, San Donato M.se, Milan, Italy.
authors: Marco
authors: M
authors: Mendola
authors: Endocrinology and Diabetology Unit, Dept. Biomedical Sciences for Health, University of Milan, IRCCS Policlinico San Donato, San Donato M.se, Milan, Italy. Electronic address: sabrina.corbetta@unimi.it.
authors: Sabrina
authors: S
authors: Corbetta
mesh_terms: D018118:Chloride Channels / Q000235:genetics*; D004252:DNA Mutational Analysis; D003937:Diagnosis, Differential; D005260:Female; D020249:Hormone Replacement Therapy; D006801:Humans; D007037:Hypothyroidism / Q000175:diagnosis / Q000188:drug therapy / Q000235:genetics* / Q000503:physiopathology*; D009154:Mutation; D009224:Myotonia Congenita / Q000175:diagnosis / Q000188:drug therapy / Q000235:genetics* / Q000503:physiopathology*; D013974:Thyroxine / Q000627:therapeutic use; D055815:Young Adult
chemical_list: C086321:CLC-1 channel; D018118:Chloride Channels; D013974:Thyroxine
keywords: CLCN1; Hypothyroidism; Myotonia congenita