Severe Hypernatraemia Secondary to Adipsia Associated With a Pituitary Macroadenoma in a Dog: A Case Report.

BACKGROUND: Adipsia is a rare disorder characterised by absence of thirst despite hyperosmolality, resulting from dysfunction of the hypothalamic thirst centre. In veterinary medicine, most reported cases of adipsia are associated with congenital forebrain abnormalities, whereas acquired causes in adult dogs are uncommon. CASE PRESENTATION: This report describes a 9-year-old neutered male mixed-breed dog presented with lethargy, anorexia, vomiting, recumbency, complete absence of voluntary water intake (adipsia) and intermittent tremors. Severe hypernatraemia (192 mmol/L) and hyperchloremia were identified on initial evaluation. Plasma aldosterone concentration was within the reference interval, excluding hyperaldosteronism. An ACTH stimulation test revealed hypercortisolemia, and abdominal ultrasonography demonstrated bilateral adrenal enlargement. Following controlled correction of hypernatraemia with intravenous fluid therapy, magnetic resonance imaging identified a pituitary macroadenoma occupying the sellar and suprasellar regions with mass effect toward the hypothalamus. Secondary adipsia due to hypothalamic compression was considered the most likely cause of hypernatraemia. Medical management with trilostane and cabergoline was initiated. Follow-up imaging demonstrated mild tumour reduction, and serum sodium concentrations remained stable with assisted water supplementation during nine months of follow-up. CONCLUSION: This case expands the recognised neurological manifestations of pituitary-dependent hyperadrenocorticism and highlights pituitary macroadenoma as a potential cause of acquired adipsia and severe hypernatraemia in geriatric dogs. CLINICAL TRIAL REGISTRATION: Not applicable.