Hypothyroidism unmasking proximal myotonic myopathy

No specific diagnostic test is available to identify patients with proximal myotonic myopathy and to distinguish them from common disorders causing si milar complaints. We describe three patients from three separate families w ho were initially diagnosed as having hypothyroid myopathy. Proximal weakne ss, stiffness and myotonia have persisted in each patient (2-10 years) desp ite the restoration of the euthyroid state. A familial pattern of autosomal dominant inheritance for proximal weakness, myotonia, and cataracts was cl early identified in one family and was likely in the other two families. DN A testing showed normal size of CTG repeat in the gene for myotonic dystrop hy. The clinical presentation of these three patients strongly suggests tha t hypothyroidism can unmask PROMM in asymptomatic individuals who carry the genetic abnormality. Other cases of 'hypothyroid myopathy' may represent e xamples of unmasked PROMM. (C) 2000 Elsevier Science B.V. All rights reserv ed.