Good afternoon and welcome to Just answer!! I am Dr. Loretta, a licensed veterinarian and I am happy to answer your question.
This condition could be a number of disease processes listed below:
Stress Induced Obsessive/Compulsive
For the allergic, this will respond to Benadryl at 1 mg per pound every 12 hrs. This is the infant liquid form at the pharmacy given with a dropper. If there is no response to this, have your vet examine Thembi to determine if there are parasites and/or infections that would require prescription medications. If Thembi is sterilized, this could be due to the lack of hormones and your vet has treatments for this. This symmetrical pattern could be caused by this condition and this is common in older cats like Thembi.
The last, stress induced OCD, may respond to Feliway. This is a feline pheromone that cats as a calming agent and will decrease anxiety.This can be purchased at the pet store.If this is not enough, your vet will have medications to help decrease anxiety and stop this skin condition.
there are metabolic diseases that can cause this symmetrical hair loss so have your vet examine Thembi and run lab work to rule these out.
Sincerely, Dr. Loretta