Hypothyroidism unmasking proximal myotonic myopathy (PROMM)

Department of Neurology, University of Milan, San Donato Hospital, Via Morandi, 30, 20097 San Donato Milanese, Milan, Italy.
Neuromuscular Disorders (Impact Factor: 2.64). 04/2000; 10(3):165-72. DOI: 10.1016/S0960-8966(99)00097-8
Source: PubMed


No specific diagnostic test is available to identify patients with proximal myotonic myopathy and to distinguish them from common disorders causing similar complaints. We describe three patients from three separate families who were initially diagnosed as having hypothyroid myopathy. Proximal weakness, stiffness and myotonia have persisted in each patient (2-10 years) despite the restoration of the euthyroid state. A familial pattern of autosomal dominant inheritance for proximal weakness, myotonia, and cataracts was clearly identified in one family and was likely in the other two families. DNA testing showed normal size of CTG repeat in the gene for myotonic dystrophy. The clinical presentation of these three patients strongly suggests that hypothyroidism can unmask PROMM in asymptomatic individuals who carry the genetic abnormality. Other cases of 'hypothyroid myopathy' may represent examples of unmasked PROMM.

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    • "There may be hyperglycemia because of insulin resistance (Moxley et al., 1997). Thyroid function tests may indicate hypothyroidism (Griggs et al., 1997; Sansone et al., 2000). Testosterone may be reduced and luteinizing hormone and follicle stimulating hormone elevated (Ricker, 1999). "
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    ABSTRACT: Myotonic dystrophy type 2 (DM2) is a clinically but not genetically heterogeneous, multisystem disorder, that is clinically similar to, but distinct from myotonic dystrophy type 1 (DM1). Initially, different phenotypes of DM2 were described by Ricker (proximal myotonic myopathy, PROMM), Ranum (myotonic dystrophy 2, DM2) and Udd (proximal myotonic dystrophy, PDM). Clinical features these three phenotypes had in common were diffuse, proximal or distal weakness, wasting, myotonia, cataract, cerebral, endocrine and cardiac abnormalities. Initially, the clinical differences between DM1 and PROMM seemed unmistakable, but meanwhile it has become apparent that the clinical differences between these entities are blurring. In 1999, Day et al., Meola et al. and Ricker et al. mapped the mutated gene of all three phenotypes to chromosome 3q. In 2001, the three different phenotypes were found to rely on the same mutation in the ZNF9 gene on chromosome 3q21.3. Although DM2 may be clinically heterogeneous, it is by result of a mutation in a single gene. The mutation responsible for DM2 is a CCTG-repeat expansion of 75-11 000 repeats in intron 1 of the ZNF9 gene on chromosome 3q21.3. Because of the clinical heterogeneity, the diagnosis of DM2 should rely on DNA analysis alone.
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