I'm sorry to hear of this with Evie. Such intense pruritis (itchiness) which has resulting in her excoriating her neck so badly usually results from a flea saliva allergy, atopy (allergies to environmental allergens such as pollens, molds, dust, or dust mites, etc), or even a food intolerance which can arise at any age and even after my patient has eaten the same food for quite some time. There's no reason to believe that long nails are responsible.
Evie's vicious cycle of itch-scratch-itch must be interrupted and that's usually done with an injection of a glucocorticosteroid such as prednisolone. Once her pruritis is controlled the search for the etiology of her pruritis can be done. Washing her neck as you've been doing is smart and may suffice to prevent secondary bacterial infection in that raw skin. I'm going to post my synopsis of the pruritic cat for you. Not all will apply, of course, but you'll get a good idea of what I need to consider...
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 Evie'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. Turning on the heater or As the weather warms at this time of year then hatches the eggs. Flea saliva allergy is usually most evident on the saddle area – the area between the edge of the rib cage and tail. 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 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 Evie's 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 because it avoids the possibility of my patient being intolerant to even a novel protein.). 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 top differentials are flea allergy dermatitis, food allergy, dermatophytosis (fungal infection), other ectoparasites (mange) and atopy (allergies to environmental allergens such as pollens, molds, dust, and dust mites, etc.).
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 respond with further questions or concerns if you wish.