Serum myoglobin in patients with thyroid dysfunction

To assess the pattern of change in serum myoglobin concentration in subjects with thyroid dysfunction. Serum samples were selected from 150 subjects with suspected thyroid disorder who were referred to the Royal Hospital, Muscat, Oman. The subjects were 35 males and 115 females, aged 14-56 years with mean +/- SD of 34.3 +/- 12.7 years. They were classified on the basis of thyroid stimulating hormone [TSH] and free thyroxine [FT4] into 3 groups, each consisting of 50 subjects: hypothyroid, hyperthyroid, and euthyroid subjects. The mean serum myoglobin concentration was higher in hypothyroid patients compared to hyperthyroid and euthyroid subjects [mean +/- SD was 38.5 +/- 23.1 micro g/L in hypothyroid; 18.1 +/- 7.0microg/L in hyperthyroid; 17.4 +/- 5.7microg/L in euthyroid]. There was a significant difference in myoglobin concentration between hypothyroid and euthyroid groups [F = 36.1, p< 0.001], however, there was no significant difference between the hyperthyroid and euthyroid groups. When the mean +/- 2SD for myoglobin in euthyroid subjects was calculated, the reference range was 6-29 micro g/L. Of the hypothyroid subjects, 29 [58%] had high myoglobin and 21 [42%] had normal myoglobin level. No significant correlation was noticed between TSH or FT4 and myoglobin in all studied subjects. Raised serum myoglobin may be observed in patients with hypothyroidism. Hence hypothyroidism should be considered in the differential diagnosis of patients with raised serum myoglobin concentration