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Welcome to JustAnswer. I'm Dr. Barbara, and I'll be happy to help you and Bandit today.
I'm sorry to hear that she is having this severe itching (pruritis). The diagnosis you have received basically just describes what is going on (itchy skin) but doesn't tell us why.
Itchy skin can of course be due to allergies to food or inhaled allergens, but it can also be due to a very occasional flea, and can be also due to hormonal imbalance.
The fact that she didn't respond to the steroid injection in December makes me think that her problem is a hormonal imbalance, like Cushing's Disease. Allergies would have responded. Did you vet run a blood profile on her along with a urinalysis. These would be the basic tests to begin to search for a cause of her condition.
Steroid injections can decrease a cat's immune system making her more prone to secondary infections. In Bandit's case her laryngitis may be a symptom of an upper respiratory infection. Or perhaps she has meowed excessively today. . .staying at the veterinary clinic? Or going to and from the clinic?
Depomedrol injections can cause diabetes in a cat, so you should be aware of that. Not all cats will be affected that way, but a good number will.