Endocrine Abstracts

JOINT3701

Introduction: The association between a toxic thyroid nodule and anterior pituitary insufficiency is rare and presents a diagnostic challenge. We report a case illustrating this unusual clinical situation, characterized by thyrotropic insufficiency with suppressed TSH but low FT4, associated with corticotropic insufficiency due to granulomatous thickening of the pituitary stalk.

Case Report: A 75-year-old female with no significant medical history presented with symptoms of hyperthyroidism (palpitations, weight loss) for four years. Initial cervical ultrasound revealed a left sub-total lobar thyroid nodule measuring 25×9 mm (EU-TIRADS 3), with a benign cytology result. She was started on carbimazole (10 mg/day) and beta-blockers. Thyroid scintigraphy confirmed a left quasi-total lobar toxic nodule. However, thyroid function tests showed a suppressed TSH (0.24 µUI/ml) with paradoxically low FT4 (0.74 ng/dl), suggesting thyrotropic insufficiency. Pituitary MRI revealed thickening of the pituitary stalk of granulomatous origin. An anterior pituitary function assessment showed low 8 AM cortisol levels (98 ng/ml), requiring hydrocortisone replacement therapy (10 mg/day).

Discussion: The association between a toxic thyroid nodule and thyrotropic insufficiency is uncommon and poorly documented in the literature. Typically, a toxic nodule leads to primary hyperthyroidism, characterized by suppressed TSH with elevated FT4 and/or FT3. In this case, the hormonal discrepancy (suppressed TSH with low FT4) suggested thyrotropic insufficiency, confirming hypothalamic-pituitary involvement. Thyrotropic insufficiency is a rare condition (prevalence: 1/16,000 to 1/80,000). It can result from infiltrative pituitary lesions, such as granulomatous hypophysitis. Granulomatous hypophysitis, particularly in sarcoidosis or tuberculosis, can lead to multiple anterior pituitary deficiencies, notably corticotropic and thyrotropic insufficiency. In our case, the thickening of the pituitary stalk suggests a granulomatous disease, although initial investigations were negative. Further diagnostic workup, including salivary gland biopsy and angiotensin-converting enzyme dosage, is ongoing to assess for sarcoidosis. Regarding management, appropriate hormonal replacement therapy is crucial. The treatment of the toxic nodule relies on radioiodine therapy, which is particularly suitable for elderly patients refusing surgery.

Conclusion: This case highlights a rare association between a toxic thyroid nodule and thyrotropic insufficiency, altering the typical biochemical profile of a toxic nodule. It underscores the importance of investigating pituitary involvement in cases of hormonal discordance and considering a granulomatous etiology when structural abnormalities of the pituitary stalk are present.