Endocrine Abstracts

Introduction: Thyroid hormones can cause sex hormone–binding globulin (SHBG) mediated elevation of total testosterone without true androgen excess. We present a case illustrating this paradox.

Case report: A 35-year-old man was referred with abnormal thyroid function tests and unexpectedly high testosterone levels, raising concern for dual endocrine pathology. Although he had symptoms of thyrotoxicosis, he had no clinical features of androgen excess. On examination, he had a diffuse goitre, exophthalmos, and hand tremors, with no gynaecomastia. Biochemical investigations showed thyroid-stimulating hormone (TSH) <0.05 mIU/l (0.2–4.2), free thyroxine (FT4) 110 pmol/l (11–23), free triiodothyronine (FT3) >50 pmol/l (3.1–6.8), total testosterone >52 nmol/l (11–28), SHBG 332 nmol/l (18–54), follicle-stimulating hormone (FSH) 9.2 IU/l (1.4–18.1), luteinising hormone (LH) 13.8 IU/l (1.5–9.3) and positive thyrotropin receptor antibodies, confirming Graves’ disease.Free testosterone could not be calculated as levels exceeded the assay limit and were suspected to be low due to profound SHBG elevation. The raised LH was therefore attributed to reduced androgen feedback. After starting carbimazole, testosterone became measurable within two months, allowing calculation of low free testosterone (6.61 nmol/l), supporting the proposed mechanism for the elevated LH. Within eight months of treatment, all biochemical parameters normalised, confirming a thyroid-driven and reversible process.

Conclusion: Hyperthyroidism causes SHBG-mediated hypertestosteronaemia rather than true hyperandrogenism (1,2). Androgen abnormalities in Graves’ disease should therefore be interpreted cautiously to avoid unnecessary investigations.

References: 1. GORDON GG, SOUTHREN AL, TOCHIMOTO S, RAND JJ, OLIVO J. Effect of hyperthyroidism and hypothyroidism on the metabolism of testosterone and androstenedione in man. The Journal of Clinical Endocrinology & Metabolism. 1969 Feb 1;29(2):164-70. 2. Ford, H.C., Cooke, R.R., Kelghtley, E.A. and Feek, C.M., 1992. Serum levels of free and bound testosterone in hyperthyroidism. Clinical endocrinology, 36(2), pp.187-192.