I'm sorry to hear of this with Cassie. Our dermatologists tell us to apply an effective over the counter flea spot-on such as Advantage, a fipronil-containing product such as Frontline or one of the newer prescription products available from Cassie's vet even if fleas aren’t seen. The newest prescription class of flea killers containing afoxolaner (NexGard) or fluralaner (Bravecto) has been shown to kill fleas faster and last longer than other classes of flea killers. Whenever you see Cassie paying too much attention to her skin between the edge of her rib cage and her rear (the "saddle area") a flea saliva allergy is most likely. Dogs can be such effective groomers so as to eliminate all evidence of flea infestation. Dogs who remain primarily indoors 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 or you turn on heaters at this time of year, egg hatches are common. In severe cases, an anti-allergenic prescription glucocorticosteroid such as prednisone will work wonders for dogs allergic to the saliva of the flea. If you have other pets they may have fleas too but may not be allergic to the flea’s saliva.
Cassie sounds as if she would benefit from a short course of prednisone. We don't want her to scratch and bite herself to the point that she ulcerates her skin (causing "hot spots"). The above said, there are other consideration in these dogs and so I'm going to post my synopsis of the pruritic (itchy) dog for you. Take your time perusing the synopsis and then return to our conversation with further questions or concerns if you wish.
(Section on flea saliva allergy omitted so as not to be redundant.)
Pruritic (itchy) dogs are suffering from an allergic dermatitis in the great majority of cases. Allergies to flea saliva, environmental allergens (atopic dermatitis) such as pollens, molds, dust and dust mites, and foods should be considered. (Paw and extremity licking indicates both atopy and a food intolerance and so it behooves vets to distinguish one from another.) In many instances, a concomitant pyoderma (bacterial skin infection), yeast infection (Malassezia), or mange mite (Demodex or Sarcoptes) might be contributory.
Casie's vet can check a sample of Cassie's skin surface microscopically (a “cytology”) for abnormal numbers of bacteria and yeast and skin scrapings can be taken in an attempt to find mites. Pyoderma is treated with a minimum of 3-4 weeks of an antibiotic in the cephalosporin class such as cephalexin (Keflex) and yeast is addressed with ketoconazole for at least a month.
Environmental allergies are usually initially addressed with prednisone as well. In some dogs an over the counter antihistamine such as clemastine (Tavist) at a dose of 0.025 - 0.75mg/lb twice daily or diphenhydramine (Benadryl) dosed at 1-2mg/lb twice daily may be effective. Antihistamines, however, aren’t reliably effective. Adding fish oil to the diet at a dose of 20mg/lb daily of the EPA in the fish oil might synergize with antihistamines to provide better anti-pruritic action. The omega-3 fatty acids in fish oil are antiinflammatory but may take 8-12 weeks to kick in. The new cytokine antagonist oclacitinib (Apoquel) is likely to revolutionize how we address atopic dogs and should be discussed with her vet. Oclacitinib works as well as a steroid without a steroid's adverse effects.
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 Sassie'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. The prescription foods are available from her vet. There are many novel protein foods and a prototypical hydrolyzed protein food is Hill’s Prescription Diet z/d ultra. (I prefer the hydrolyzed protein diets.) A positive response is usually seen within a few weeks if we’ve eliminated the offending food allergen. Food intolerance can arise at any age and even after our patient has been eating the same food for quite some time.
We need to consider seborrhea in such a patient as well. This is skin disorder of keratinization and maturation. It's a diagnosis of exclusion of the above mentioned skin disorders and can be suggested by skin biopsy.