Hypercalcemia Due to Iatrogenic Secondary Hypoadrenocorticism and Diabetes Mellitus in a Cat

A 9-year-old, spayed female domestic shorthair cat presented for polyphagia, polydipsia, and polyuria following chronic methylprednisolone acetate therapy for pruritus. Initial diagnostics were consistent with uncomplicated diabetes mellitus. Serum calcium was within reference range. Within 12 hours the cat developed depression, anorexia, vomiting, and severe dehydration. Laboratory analysis indicated marked hypercalcemia as measured by both ionized and total calcium concentration. No underlying neoplastic or inflammatory process was identified. An adrenocorticotropic hormone stimulation test was indicative of adrenocortical insufficiency. The hypercalcemia resolved with glucocorticoid supplementation and correction of the dehydration. The diabetes mellitus and adrenal insufficiency both resolved within 9 weeks.