Muscle mass and function in thyrotoxic patients before and during medical treatment

OBJECTIVE Development of muscle weakness and atrophy are well known complic ations of thyrotoxicosis, although little is known about its clinical cours e, The present longitudinal study was therefore undertaken to monitor muscl e mass and strength before and during treatment of hyperthyroidism. DESIGN AND PATIENTS Five patients (2 male, 3 female; Age 41 +/- 6 years; BM I 22.2 +/- 1.1 kg/m(2)) with newly diagnosed hyperthyroidism were studied w ith respect to muscle area, muscle strength, body composition and substrate metabolism at baseline and after 1, 3, 6, 9 and 12 months of treatment. MEASUREMENTS Midthigh muscle areas were assessed by computed tomography (CT ), while bioelectrical impedance analysis (BIA) was used for assessment of body composition, The isometric strength of the biceps brachialis and quadr iceps muscles was assessed by means of a dynamometer and the maximal static ins- and ex-piratory mouth pressures were measured with a respiratory pres sure module. RESULTS Prior to treatment thyrotoxic patients all displayed elevated level s of total and free T-3 and T-4 together with suppressed TSH. BMI, fat mass and lean body mass increased significantly during the treatment period, wh ile energy expenditure (EE) decreased. Thigh muscle areas increased by 24% (101.5 +/- 11.5 vs, 125.3 +/- 13.1 cm(2), P <0.05) from entry to peak. Peak time was 9 +/- 0.9 months. During treatment a significant (P <0.01) increa se in muscle strength was observed; arm capacity increased by 48%, while le g capacity increased by 51%, Peak time (months) was: Right arm: 8 +/- 3, le ft arm: 7 +/- 2, right leg: 5 +/- 3, left leg: 9 +/- 2. Respiratory muscle strength, expressed as maximal ins- or ex-piratory mouth pressure, was sign ificantly impaired among patients at entry. A significant increase in inspi ratory and expiratory strength was found from entry to peak (P <0.05), as i nspiratory strength increased by 35% and expiratory by 19%, Inspiratory str ength peaked after 7 +/- 1 months, expiratory muscle strength after 6 +/- 1 months. CONCLUSIONS In conclusion we find that in patients with thyrotoxicosis musc le mass is reduced by approximately 20% and muscle strength by approximatel y 40% and that between 5 and 9 months elapse before normal muscle mass and function are reestablished.