Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that Sully has slight hair loss on the back of his ears.
Because he is scratching this sounds like he may be traumatizing his ears leading to the hair loss.
I know it is hard to get him there but I would recommend an examination by your veterinarian to look for contagious diseases. I would take a swab and scraping of the ear skin to look for evidence of mites, sarcoptic and demodex, and collect material for a ringworm
culture as these are the most common causes of ear hair loss affecting cats. Sometimes mites can be difficult to find, especially in early infestations.
Other less common reasons for hair loss are related to endocrine diseases such as hyperthyroidism
, or Cushing's Disease (an overactive adrenal gland). Testing is done via a complete thyroid profile or just a T-4 for thyroid disease and an ACTH response test for adrenal disease. These cats are not usually itchy though.
Autoimmune skin disease (body attacking itself) is a possibility if his ears were crusty and ulcerated along with fur loss. Diagnosis is via a skin biopsy. Treatment is immunosuppressive drugs such as steroids.
Finally a condition called Feline Pinnal Alopecia is possible. This occurs most commonly in Siamese and Siamese mixes. The hair loss areas are smooth and not itchy. It may be patchy or involve the entire ear. Hair may spontaneously regrow.
Treatment is usually unrewarding but some recommend Melatonin orally at 1/4mg per pound of body weight every 12 hours. That's 2.5mg per 10 pound cat every 12 hours.
There are a few things that you can do at home now while waiting to get him examined. You can give a combination of antihistamines and omega 3 fatty acids to help with the itchy feeling. You can use either:
1) chlorpheniramine 4mg at half to one full tablet orally every 12 to 24 hours
2) Benadryl (diphenhydramine) at half of a 25mg tablet per 8 to 15 pound cat every 8 to 12 hours (1mg to 2mg per pound of body weight every 8 to 12 hours).
3) Zyrtec (Cetirizine hydrochloride) at a dose of 5 mg per cat given orally every 24 hours. (Make sure it is NOT the formulation with a decongestant (such as Zyrtec-D) because cats cannot tolerate decongestants.)
Antihistamines can cause sleepiness or hyperactivity in some cats but those effects usually wane with repeated use.
Good brand name omega 3's to try are 3V Caps or Derm Caps. I recommend a dose based upon the EPA portion (eicosapentanoic acid) of the supplement as if we do that the rest of the supplement will be properly balanced. Give him 20mg of EPA per pound of body weight per day. For example an 8 pound cat could take 160mg of EPA per day. Together antihistamines and omega-3 fatty acids work synergistically. These should help reduce the itch.
You can also gently clean the inside of his ears if they are waxy with an ear cleaner like Oticlens to remove any waxy debris.
Best of luck with your kitty, please let me know if you have any further questions.