Concurrent somatotroph and plurihormonal pituitary adenomas in a cat

An 8-year-old, male neutered, domestic longhair cat was referred for investigation of insulin-resistant diabetes mellitus. Routine haematology, serum biochemistry, urinalysis (including culture), total T4 and urine creatinine:cortisol ratio were unremarkable, but markedly increased insulin-like growth factor-1 concentration was identified and a pituitary mass was subsequently documented. The cat was treated conservatively with the dopamine agonist L-deprenyl and was re-presented 16 months later for worsening polyuria, polydipsia, polyphagia, marked lumbar muscle atrophy, development of a pendulous abdomen and marked thinning of the abdominal skin. Hyperadrenocorticism was diagnosed based on abdominal ultrasonography, dexamethasone suppression testing and endogenous adrenocorticotropic hormone (ACTH). The cat was treated with trilostane (30 mg q24h PO) and showed some clinical improvement, but developed an opportunistic fungal infection and skin fragility syndrome 4.5 months after commencing treatment, and was euthanased. A double-pituitary adenoma comprising a discrete somatotroph adenoma and a separate plurihormonal adenoma (positive immunoreactivity for ACTH, melanocyte-stimulating hormone and follicle-stimulating hormone) was identified on post-mortem examination. These two pituitary adenomas were suspected to have arisen as independent neoplastic entities with the plurihormonal tumour either being clinically silent at the initial presentation or having developed over the subsequent 16 months.