Relationship between Thyroid Function and Skeletal Muscle Involvement in Subclinical and Overt Hypothyroidism

It is not well known how often the skeletal muscle is involved in hypothyroidism and if there is a relation between the severity of hypothyroidism and the degree of skeletal muscle involvement. This prospective, observational study investigated the frequency of muscle symptoms, symptoms of hypothyroidism, elevated serum creatine kinase (CK) and the relation between CK and thyroid function tests. During 6 months, 69 patients, aged 16–87 years, in whom hypothyroidism was newly diagnosed were studied. Sixty-one patients had subclinical and eight had overt hypothyroidism. Twenty-five percent had muscle symptoms. Muscle symptoms were observed in 16 patients with subclinical and 1 patient with overt hypothyroidism. Symptoms of hypothyroidism were equally frequent in patients with (82%) and without (88%) muscle symptoms. CK was elevated in 3%. CK levels were not related to any of the thyroid function tests. In conclusion, the relation between the degree of skeletal muscle involvement and the severity of hypothyroidism in patients with subclinical and overt hypothyroidism is poor. CK is only rarely elevated in these patients. The skeletal muscle is less frequently involved in patients with hypothyroidism than previously reported.