Lessons of the month: A challenging presentation of hypopituitarism secondary to an intracerebral aneurysm.

A 65-year-old man presented to ambulatory care with a 10-month history of muscle weakness, weight loss, dysphagia and fatigue.Prior to presentation he had been managed in general practice for hypothyroidism with a low T4 level and normal thyroid stimulation hormone (TSH). He was commenced on levothyroxine yet, despite dose titrations, had ongoing symptoms. He had been extensively reviewed by gastroenterology and rheumatology teams.The thyroid function tests (TFTs) pattern prompted a pituitary hormone profile test, which revealed panhypopituitarism with a cortisol of 22 nmol/L. Therefore, hydrocortisone was commenced. A pituitary magnetic resonance imaging (MRI) detected a left internal carotid aneurysm that was confirmed on computed tomography angiography. He successfully underwent embolisation of the aneurysm in the local neurosurgical centre.This case highlights the importance of correctly interpreting TFTs as this patient's initial TFTs indicated central hypothyroidism which should have prompted urgent pituitary hormone screening. The risk of addisonian crisis with commencement of levothyroxine without steroid replacement in secondary hypothyroidism emphasises the importance of TFT interpretation. Internal carotid artery aneurysms are a rare, yet important, cause of hypopituitarism resulting in high mortality and morbidity associated with delayed diagnosis secondary to the pressure effects of the aneurysm or the effects of aneurysmal rupture. © Royal College of Physicians 2021. All rights reserved.