Endocrine Abstracts

Introduction: Hyperpigmentation is a clinical sign that can be associated with different endocrine disorders. It is commonly seen in Addison’s disease and has rarely been reported in Graves’ disease. The exact physio pathological mechanism of this sign is not well established in hyperthyroidism. We describe two cases of Graves’ disease accompanied by diffuse hyperpigmentation.

Case report: Case 1 was a 63-year-old female admitted to the endocrinology department for the management of a thyroid crisis. The physical examination didn’t find signs of thyroid eye disease or goiter, we instead noted diffuse hyperpigmentation. Laboratory investigations confirmed the diagnosis of hyperthyroidism showing a 6-fold elevation of FT4 (7.7; normal: 0.9-1.7 ng/dl) and low serum thyroid-stimulating hormone (TSH <0.001 mIU/l) with positive anti-TSH receptor antibodies. Hepatic function tests revealed cytolysis and cholestasis. Addison’s disease and autoimmune hepatic diseases were eliminated. The patient received radioiodine treatment after preparation with antithyroid drugs. She regained euthyroidism with normalization of her liver function tests, but hyperpigmentation persisted.

Case 2 is a 52-year-old male patient who presented to our department with Graves’ disease. He had clinical signs of hyperthyroidism a few months before admission with a concomitant change of his skin color. On physical exam, we noted irregular tachycardia with goiter. The patient had diffuse hyperpigmentation. Hyperthyroidism was biologically confirmed; high serum free T4 (10.3 ng/dl) with low serum thyroid-stimulating hormone (TSH <0.001 mIU/l). Anti-TSH receptor antibodies were positive. The rest of the explorations revealed cholestasis with normal transaminase levels. The patient was treated with radioiodine with clinical and biological amelioration. However, hyperpigmentation remained.

Discussion: Hyperpigmentation is rarely described as a clinical sign of hyperthyroidism. Its physiopathological mechanism is not well elucidated. It has been hypostasized that thyrotoxicosis is associated with an increased ACTH release causing overproduction of melanin and that melanocytes express TSH receptors resulting in their proliferation when stimulated with TRAb. More studies are needed to understand the relationship between skin color modification and thyroid function status.