Endocrine Abstracts

A 19-year-old, female of West African descent presented with a 5 months history of thyrotoxicosis. The GP had commenced carbimazole. She had continuing clinical and biochemical thyrotoxicosis TSH <0.01 (0.3–5.5 mU/l), FT₄ 68.0 (9–20 pmol/l) and FT₃ 18.9 (3.4–5.6 pmol/l). Thyroid antibodies were present at elevated titre and technetium uptake scanning showed toxic diffuse hyperplasia with an uptake function of 37%, confirming Graves’ disease.

A random cortisol was measured and reported as <30 nmol/l (mid-morning sample). A further 0900 h measurement was 184 nmol/l with simultaneous ACTH of 16 ng/l. Hydrocortisone therapy was commenced and a short synacthen test (SST) arranged within a week of presentation. Hydrocortisone was discontinued 24 h prior to the SST.

Hydrocortisone was continued following the SST. We repeated the SST 1 month later when the patient was clinically euthyroid (TSH 0.01, FT₄ 5.8 pmol/l and FT₃ 6.1 mol/l). Adrenal cortex antibodies were negative. Hydrocortisone was cautiously withdrawn with monitoring of random cortisol levels which were around ~400 nmol/l.

She had prolonged periods of non-adherence with carbimazole. Nine months after presentation she had a FT₄ 67 pmol/l, FT₃ 35.4 pmol/l. ACTH <10, cortisol 117 nmol/l and cortisol binding globulin 33.6 (31–53 mg/l). Eventually after a short period of greater adherence she underwent total thyroidectomy having declined treatment with radioiodine.

Conclusions: We report low cortisol levels with inappropriately low ACTH during a prolonged episode of hyperthyroidism. Interpretation of cortisol values in the setting of hyperthyroidism is not straightforward.