Endocrine Abstracts

With treatment of endocrine myopathies increased proximal muscle strength is generally attributed to increased bulk. However in hypothyroid myopathy individuals have been shown to increase strength despite reduction in bulk.

We studied 25 hyperthyroid and 27 hypothyroid randomly selected patients, measuring body weight, quadriceps and deltoid force using strain gauge techniques or with a myometer. Cross sectional area (CSA) of the quadriceps and Right deltoid muscle was measured using CT. Quadriceps/deltoid force/kg body weight (QF/kg and DF/kg), quadriceps/deltoid force/unit CSA (Q/D, F/CSA) were derived and these measurements repeated after patients were biochemically euthyroid for several months. Paired t tests were used for statistical analysis.

Treatment of hyperthyroidism caused QF/kg and DF/kg to rise significantly, n=25, p<0.0001, as did quadriceps CSA in each limb and deltoid CSA invariably, n=24, p<0.0001. R QF/CSA, n=24 and RDF/CSA, n=23 also rose significantly with treatment, p<0.0001. In treated hypothyroidism QF/kg, n=27, rose in each limb (p<0.0001) and DF/kg, n=25 rose significantly p=0.038 for right and p<0.0001 for left. Quadriceps CSA decreased significantly, n=27, Right p<0.0001, Left p=0.020. R deltoid CSA decreased but NOT significantly, n=25, p=0.064. QF/CSA, n=27 increased significantly in each limb p<0.0001, as did R DF/CSA, n=23 p=0.024.

Conclusions. Proximal muscle force/kg increases significantly with treatment in both disorders. In hypothyroidism bulk decreases so increased F/CSA is the cause of increased strength whereas in hyperthyroidism both increased bulk and F/CSA are responsible