Case summary A 1-year-old neutered male domestic shorthair cat was presented for polyuria and polydipsia which had progressed since adoption, 7 months previously. On admission, clinical examination did not reveal any remarkable features. Urinalysis showed marked hyposthenuria and calculated plasma osmolality was high, suggesting diabetes insipidus. A positive response to desmopressin administration appeared to confirm pituitary dysfunction. Brain MRI revealed a lesion compatible with a cyst or a neoplasm compressing the pituitary gland. A follow-up MRI performed 9 months later showed that the lesion was stable, which at first argued in favour of a congenital pituitary cyst. Intranasal administration of desmopressin was then used to achieve a long-term clinical response.

Relevance and novel information Central diabetes insipidus (CDI) is a rare cause of polyuria and polydipsia in cats, resulting from inadequate or impaired secretion of antidiuretic hormone from the posterior pituitary gland. Recognised causes include head trauma, central nervous system (CNS) neoplasia, idiopathic CDI and congenital pituitary cysts. Apart from one cat with CNS lymphoma, the few previously reported feline cases have described CDI in young cats with a previous history of trauma, but brain imaging has rarely been performed to look for underlying anatomical abnormalities. This report describes the first case of CDI in a cat with a confirmed congenital pituitary cyst and, as in previous cases, demonstrates successful treatment with desmopressin.