Fluctuating clinical myotonia and weakness from Thomsen's disease occurring only during pregnancies

Advances in molecular genetics are allowing better phenotype to genotype co rrelation of the non-dystrophic myotonic disorders. We report a 32-year-old woman, who first noted myotonia that was associated with weakness during h er first pregnancy. The work-up disclosed that she had Thomsen's disease wh ich is not known to be associated with weakness. In addition, her myotonia was of the fluctuating type and occurred (symptomatically) only during two pregnancies. We discuss the evaluation of myotonia in the pregnant woman wh ich led to the diagnosis of Thomsen's disease and we conclude that in excep tional cases, fluctuating myotonia and weakness occurs in autosomal dominan t chloride channel myotonia (Thomsen's disease). (C) 1999 Elsevier Science B.V. All rights reserved.