Have Cat Questions? Ask a Cat Vet Online.
Have you switched her food and water dishes to steel or ceramic - I know you ruled out plastic but just making sure :>) ?
Have you tried a different cat food (for more than 3-4 weeks at one time)?
The most common treatment for feline acne is Bactroban ointment used twice a day for three weeks.
I would not rule out demodecosis even though they have already scraped for mites. It's sometimes hard to dianose by scraping the skin of cats. Ivermectin can be successfully used to treat demodectic mange in cats. You would have to check with your vet for a dosage. With demodex, it's best to treat the patient from the inside out. That means being sure that the cat is receiving the proper nutrion, extra fatty acids and vitamins. It IS an immune disorder. Your vet can help you find the ingredients to make the perfect "cocktail" for your pet.
Other possibile causes are ringworm, yeast infections, and allergies.
If you have not yet seen a veterinary dermatologist, you should probably do so.
We see this a lot in our feral cat communities and it's difficult to treat.
The disease is called demodectic mange. It sounds remarkably like what you are experiencing. It ban be detected by scraping the skin but the scrapes are not always conclusive.
New therapy for the condition implements the use of ivermectin (cattle wormer) to treat it.
All cats have mites on the skin, as do people. Usually, our immune systems are strong enough to fight them. If the immune systems is compromised, the mites can take over and you will see resulting hair loss, itching, red, flaky skin. It also predisposes your cat to secondary fungal infections. This condition is often hereditary, as is evidenced by the fact that the cat's sibling has it as well.
You should talk to your vet about the use of ivermectin to treat this. Also, speak with him about the use of fatty acids and vitamin supplements to build the immune system.
Let me know if you still have questions.
Sorry for my absense - thank you Tammy for taking over and replying to the questions. I, too believe the vet should be more assertive in skin scrapings or skin biopsy. Whatever mange it is, may take time to clear up however if it is properly diagnosed it can then be properly treated and cared for. The choice for most is ivermectin.
I don't understand the comment on the cat food causing mites or having mites? Maybe I'm misunderstanding.
If the possibility of a food allergy is part of the problem, there are many allergen free cat foods on the market you could try - or supplements as suggested above.
I hope we have helped guide you and your kitty is on the road to recovery very soon!