title: The impact of overt and subclinical hyperthyroidism on skeletal muscle.
abstract: OBJECTIVE
  Patients with overt hyperthyroidism (OH) commonly have proximal limb muscle weakness that improves after correction of hyperthyroidism. It is unclear, however, if patients with milder degrees of hyperthyroidism (referred to as subclinical hyperthyroidism or SCH) may also have a degree of muscle weakness. This may have clinical relevance as SCH patients are often elderly and may therefore have concurrent sarcopenia of aging and would represent a previously unrecognized complication of SCH.
  
  
  METHODS
  We measured both thigh strength and cross-sectional area in patients with OH (n = 30) or SCH (n = 24), both prior to treatment of hyperthyroidism and again at 6-9 months after the restoration of a euthyroid state. Euthyroid controls (n = 48) were studied at similar time intervals.
  
  
  RESULTS
  Prior to treatment, both knee flexor and extensor muscle strength was reduced in both patients with OH and SCH compared to controls (p < 0.05). After treatment all strength measurements improved in the OH group (p < 0.01) while in the SCH group the majority of muscle strength measurements improved (p < 0.05). Midthigh muscle cross-sectional area was reduced in both the OH and SCH group at baseline (p < 0.05) compared to controls and increased significantly following treatment (p < 0.05). There were no significant changes in any parameter in the euthyroid control (EC) group during the study period.
  
  
  CONCLUSIONS
  The finding that muscle strength and cross-sectional area are reduced in SCH and improved after treatment lends support for the clinical decision to treat rather than observe this condition. This may have particular relevance to certain SCH patient groups including the elderly who are prone to falls and athletically active younger patients who require optimal skeletal muscle function.
authors.affiliation: Division of Endocrinology, Diabetes, Nutrition & Metabolism, Mayo Clinic, Rochester, Minnesota 55905, USA. brennan.michael@mayo.edu
authors.forename: Michael D
authors.initials: MD
authors.lastname: Brennan
authors.forename: Claudia
authors.initials: C
authors.lastname: Powell
authors.forename: Kenton R
authors.initials: KR
authors.lastname: Kaufman
authors.forename: Pi Chang
authors.initials: PC
authors.lastname: Sun
authors.forename: Rebecca S
authors.initials: RS
authors.lastname: Bahn
authors.forename: K Sreekumaran
authors.initials: KS
authors.lastname: Nair
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D006980:Hyperthyroidism / Q000150:complications / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology; D018908:Muscle Weakness / Q000209:etiology*; D018482:Muscle, Skeletal / Q000473:pathology / Q000503:physiopathology; D013972:Thyrotropin / Q000378:metabolism
chemical_list: D013972:Thyrotropin