Addison's Disease can also occur in felines!

• Addison’s disease, or hypoadrenocorticism, is much more common in dogs than cats, but does occasionally occur in kitties. In Addison’s disease, the adrenal glands become overworked and are no longer able to produce a sufficient amount of corticosteroid hormones.

• Feline hypoadrenocorticism is usually caused by atrophy of the adrenal glands resulting from an autoimmune problem. Other possible causes of Addison’s in cats include the use of corticosteroid drugs, cancer, damage to the pituitary gland, and infection.
• Cats with Addison’s may not show any obvious signs of illness. In symptomatic kitties, the signs of disease can be broad, and can come and go. They include weakness, lack of energy, loss of appetite, increased thirst and urination, vomiting, and sudden collapse. Since symptoms of hypoadrenocorticism are typical of many other feline diseases, hopefully your veterinarian has considered Addison’s as a possibility. The confirming test for Addison's is an adrenocorticotropin hormone (ACTH) stimulation test.
• How aggressively your cat’s illness is treated will depend on her symptoms and overall clinical status. An acute Addisonian episode is a real emergency requiring immediate veterinary care. Very sick cats must be hospitalized to receive IV fluids and cortisol replacement agents, and it can take three to five days or longer before improvement is seen. Long-term care of Addison’s disease usually involves oral supplementation with adrenal corticosteroid hormone replacement for the rest of the cat’s life.
• Because hypoadrenocorticism is a serious disorder, it’s very important to help your cat avoid the problem in the first place. Steps you can take include feeding a species-appropriate diet, avoiding unnecessary vaccinations, providing a stress-free enriched environment, and discussing appropriate supplements with your holistic veterinarian. 

Source: Healthy Pets by Dr. Karen Becker