Thyroid abnormalities in patients with myotonic dystrophy

Myotonic dystrophy (MD) is a systemic genetic disorder predominantly affecting musculature. Although endocrine disturbances have been described, data relating to thyroid gland involvement are sparse and conflicting. To further investigate this aspect, twenty MD patients and twenty age-and sex-matched controls were studied. All were clinically euthyroid and there were no significant differences between circulating levels (mean +/- SD) of T4 (101 . 5 +/- 28.2 v. 103 . 8 +/- 27 . 7 nmol/l), T3 (1 . 86 +/- 0 . 57 v. 2 . 15 +/- 0 . 47 nmol/l), rT3 (0 . 39 +/- 0 . 14 v. 0 . 42 +/- 0 . 09) nmol/l) or TSH (2 . 6 +/- 0 . 5 v. 2 . 4 +/- 0 . 8 mu/l) or between T3 resin uptakes (97 +/- 8 v. 98 +/- 11%). TSH responses following TRH stimulation were significantly less in the MD patients (323 +/- 141 v. 529 +/- 240%; P less than 0.0025). The mean maximum TSH levels achieved were 6 . 7 +/- 3 . 6 mu/l (MD) and 17 . 1 +/- 7 . 2 mu/l (controls); P less than 0.005. Two patients had multinodular goitres (MNG) and one a single thyroid nodule. Thyroid scans were normal except for patchy uptake in the two MNG patients. There was no abnormal incidence of circulating thyroid microsomal or thyroglobulin antibodies, and thyrotrophin binding inhibitory immunoglobulin levels were normal in four patients. It is concluded that in MD: 1 palpable thyroid gland abnormalities occur with increased frequency, 15% (three/twenty) in the present study and 20% (twenty/102 case reports) from a review of the literature; 2 TSH responses to TRH are significantly reduced; 3 circulating thyroid hormone levels are usually normal.