Endocrine Abstracts

Introduction: Thyrotropin deficiency is a rare etiology of hypothyroidism. The diagnosis can be easily confirmed in case of low FT4 level associated with normal or low TSH value. In patients with peripheral hypothyroidism treated by levothyroxine, this biochemical profile become difficult to find. Herein, we describe the case of a patient with peripheral hypothyroidism due to radioiodine therapy in whom the diagnosis of central hypothyroidism was made.

Observation: An 80-year-old patient, type 2 diabetic, followed initially, 15 years ago, for Graves’ disease treated by radioiodine then he received levothyroxine for peripheral hypothyroidism. The replacement dose has been decreased gradually from 150µg q.d. to 75µg q.d. before the patient withdrew his treatment 4 months ago. The patient was admitted in our department for intense asthenia and hypoglycemia. He didn’t take any medication recently. His renal and hepatic functions were normal. His TSH level was normal for his age at 5 μUI/l although the history of radioiodine therapy. Endocrinological assessment confirmed central hypothyroidism with low FT4 at 7 pmol/l (12-22 pmol/l), corticotropin deficiency with peak cortisol level after Synacthene test at 185 nmol/l and hypogonadotropic hypogonadism with a testosterone level at 0.22 ng/ml. His prolactin level was low at 68 IU/l. Pituitary MRI showed anterior pituitary hypoplasia and pituitary stalk thickening of 4 mm. hydrocortisone replacement therapy was prescribed at the dose of 15 mg q.d. in addition to levothyroxine at the dose of 75 µg q.d.

Conclusion : Decreased levothyroxine requirements in a patient with peripheral hypothyroidism, the persistence or the presence of nonspecific symptoms although normal TSH level should guide clinicians to the diagnosis of thyrotropin deficiency, most frequently associated with other pituitary hormone deficiency.