Aloha! You're speaking with Dr. Michael Salkin
I'm going to post my synopsis of the pruritic (itchy) cat for you so you have a broad overview of these cats. My working diagnosis for a cat non-responsive to a corticosteroid such as prednisone is demodectic mange (uncommon), psychogenic alopecia if her abdomen and inner limbs are the primary sites of hair loss, and a food
I'm sorry to hear of this with Nina. Pruritic (itchy) cats are suffering from an allergic dermatitis the great majority of the time. Allergies to flea saliva, environmentals such as pollens, molds, dust and dust mites, and foods should be considered. In rare instances the mange mite Demodex might be responsible.
Our dermatologists tell us to apply an effective over the counter flea spot-on such as Advantage or a fipronil-containing product such as Frontline or one of the newer prescription products available from Nina's vet even if fleas aren't seen. Cats can be such effective groomers so as to eliminate all evidence of flea infestation. Indoor cats can contract fleas because we walk them in on us and flea eggs and larva can remain viable in your home for months. As the weather warms at this time of year, egg hatches are common. In severe cases, an anti-allergenic prescription corticosteroid such as prednisolone will work wonders for cats allergic to the saliva of the flea. Your other pets may not be allergic to the saliva of the flea.
Environmental allergies are usually addressed with prednisolone as well. In some cats an over the counter antihistamine such as chlorpheniramine (Chlor-Trimeton) dosed at 2mg/cat daily or diphenhydramine (Benadryl) dosed at 1-2mg/lb twice daily may be effective.
Food intolerance/allergy - an important consideration in Nina - is addressed with prescription hypoallergenic diets. These special foods contain just one novel (rabbit, duck, e.g.) animal protein or proteins that have been chemically altered (hydrolyzed) to the point that her immune system doesn't "see" anything to be allergic to. The over the counter hypoallergenic foods too often contain proteins not listed on the label - soy is a common one - and these proteins would confound our evaluation of the efficacy of the hypoallergenic diet. There are many prescription novel protein diets and the prototypical hydrolyzed protein diet is Hill’s Prescription Diet z/d ultra (I prefer a hydrolyzed protein diet). We usually see a positive response to these foods within a few weeks if we’ve eliminated the offending food allergen. A food intolerance can appear at any age and even if our cats have been eating the same food for quite some time.
We used to diagnose these cats with psychogenic alopecia - a neurotic over-grooming - but have come to realize that most of these cats truly are allergic cats. Feline psychogenic alopecia is overdiagnosed but does exist. Excessive and out-of-context grooming is thought to be an obsessive-compulsive behavior that's triggered by environmental stresses and anxiety. The condition is uncommon in cats, with purebred cats that have high-strung nervous temperaments being possibly predisposed.
This type of alopecia may occur anywhere on the body where the cat can lick but it most commonly involves the medial forelegs, inner thighs, perineum, and ventral abdomen. Hair loss is often bilaterally symmetrical but remaining hairs don't epilate easily. The underlying cause of the psychological stress (e.g., separation from owner, moved to a new house, animal companion died, new pet in household, formerly outdoor cat denied access to outdoors) must be identified and appropriate environmental modifications made, if possible. A good flea control program should be instituted to prevent fleas from aggravating the symptoms. Use of a mechanical barrier (e.g. Elizabethan collar, T-shirt) for 1-2 months to prevent grooming may help break the habit. Behavior-modifying drugs may help stop the abnormal grooming behavior. In some cases, treatment may be discontinued after 30-60 days of therapy; in others, lifelong therapy is required for control. Drugs that may be effective include the following: amitriptyline, clomipramine, buspirone, phenobarbital, diazepam, and naloxone. Please note that a week's worth of Prozac (fluoxetine) isn't enough to evaluate the response of a psychotherapeutic drug and an SSRI such as fluoxetine isn't the class of drug I usually initially reach for when addressing a psychogenic alopecia.
Please respond with further questions or concerns if you wish.