Hypoadrenocorticism in cats: a 40-year update.

Practical relevance: Addison's disease is a very rare condition in cats, with only approximately 40 cases documented in the past 40 years since it was first described in 1983.

Clinical challenges: While canine hypoadrenocorticism is a well-recognised disorder with clear diagnostic and treatment guidelines, feline hypoadrenocorticism remains a challenge because of its rarity and waxing and waning clinical signs. Furthermore, empirical treatment with corticosteroids, resulting in clinical improvement, contributes to delays in achieving the diagnosis and initiating treatment. Feline hypoadrenocorticism is diagnosed with an adrenocorticotropic hormone (ACTH) stimulation test; a low resting cortisol concentration with an inadequate or absent response to synthetic ACTH is diagnostic. Various ACTH stimulation-testing protocols are reported in published cases, with the majority using three time-limited blood samples. This can be limiting clinically, depending on cats' clinical presentation and behaviour at the veterinary practice and tolerance for procedures. Long-term treatment, similar to canine hypoadrenocorticism, consists of oral corticosteroids, with several formulations licensed in the UK, and mineralocorticoids (desoxycorticosterone pivalate), of which the only available formulation (Zycortal; Dechra) is licensed for dogs and its safety has not been assessed in cats.

Global importance: Feline hypoadrenocorticism occurs worldwide. Although no breed, sex or age association has been reported, cats aged <6 years are overrepresented.