Endocrine Abstracts

De novo vasopressin insufficiency (VI) is extremely rare in patients with pituitary adenoma who have not had biopsy or surgery and raises the question of differential diagnoses including malignancy and infective or inflammatory disease affecting the pituitary. Here we present a case of a patient initially presenting with cystic pituitary adenoma subsequently developing VI. A 24 year old woman presented to her GP with headache and secondary amenorrhoea. MRI brain revealed a cystic pituitary lesion. Pituitary MRI demonstrated a 17 mm, T1 hyper-intense proteinaceous cyst with a suprasellar component and significant displacement of the infundibulum of normal thickness. She was found to have a persistently elevated prolactin in primary care at around 900 mU/l and referred to Endocrinology. Initial early morning basal pituitary function showed persistent monomeric hyperprolactinaemia (prolactin 896 mU/l [100-550 mU/l ]) and borderline secondary hypothyroidism (TSH 1.57 [0.3-4.2 mU/l], free T4 8.0 [9-23 pmol/l], free T3 3.3 [2.4-6 pmol/l]), but otherwise normal pituitary function. Repeat serial pituitary MRIs have shown progressive spontaneous reduction in size of the pituitary lesion from the original scan in December 2021 of 17 mm × 11 mm × 12 mm to 11 mm × 3 mm × 5 mm in January 2023 with resolution of the suprasellar component, resolution of the high signal on T1 imaging and reduction in the infundibular deviation. Images were reviewed in local radiology meeting and felt to represent probable resolution of haemorrhage into a cystic pituitary adenoma. This has been accompanied by spontaneous restoration of regular menses and fully normalisation of anterior pituitary function. She had originally reported excessive thirst with no polyuria on initial assessment in endocrine clinic, on subsequent review she reported marked polydipsia, polyuria and nocturia, passing up to 11L of urine daily. Formal water deprivation test confirmed VI. On review of serial imaging and biochemistry in the regional pituitary MDT, the images were still felt to be most consistent with a cystic adenoma of the pituitary. There was an absence of the posterior pituitary bright spot. There were no imaging features suggestive of inflammation, furthermore the patient had never received steroids which could have treated an undiagnosed inflammatory lesion. In view of the spontaneous reduction in size of the lesion, malignancy was not suspected. She is currently being managed with intranasal desmopressin. We plan to re-image in 6 months and reassess clinically for resolution of VI.Does the panel have any thoughts on further differential diagnosis or management strategy?