I'm sorry to hear of this with Sparky. It's important to recognize that miliary dermatitis need not be due to flea saliva allergy. I'll post my entire synopsis of miliary dermatitis for your perusal.
I'm sorry to hear of this with Sparky. You appear to be describing a skin condition called miliary dermatitis - a papulocrustous (crusty bumps) eruption seen mainly secondary to allergic skin disease. It's prudent to also consider pyoderma (bacterial skin infection) secondary to an allergy which is more common than previously thought in cats. In rarer cases, we'll find the demodectic mange mite which can be found upon examining skin scrapings microscopically.
Athough the pattern of skin pathology can be misleading as it pertains to its cause in cats, whenever the area between the edge of a cat's rib cage to the tail is involved, a flea saliva allergy is most likely. Even if you can't find any fleas, it's best that you apply an effective over the counter flea spot-on such as Advantage/Advocate or a fipronil-containing product such as Frontline or one of the newer flea spot-ons available from Sparky's vet. In severe cases, we can either inject or orally administer a prescription antihistaminic glucocorticoid (steroid) such as prednisolone which often works wonders in these cats. Antihistamines such as diphenhydramine (Benadryl) and chlorpheniramine (Chlor-Trimeton) aren't reliably effective against allergic skin disease but you might see how a dose of 2 mg of an over the counter chlorpheniramine once or twice daily affects him. Please note that cats can be such effective groomers as to remove all evidence of fleas. It's important to still use the flea products.
Be sure to treat your premises with a product such as over the counter Siphotrol Area Treatment spray which contains the insect growth regulator (IGR) methoprene which doesn't allow flea eggs and larvae to develop into adult fleas thus breaking up the life cycle of the flea. Avoid inefficient foggers which can't reach under furniture or into cracks and crevices where flea eggs and larvae are found.
Less commonly but still important, Sparky's skin can result from food intolerance or atopy (allergies to environmental allergens such as pollens, molds, dust and dust mites, etc.) 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 his immune system doesn't "see" anything to be allergic to. 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 Sparky's vet. There are many novel protein foods and a prototypical hydrolyzed protein food is Hill’s Prescription Diet z/d ultra (my preference). 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.
Atopy is usually initially addressed by the same prednisolone I mentioned above and used to address a flea saliva allergy. Prednisolone can be used as a test when differentiating a flea saliva allergy or atopy from food intolerance. Both a flea saliva allergy and atopy are usually quite responsive to prednisolone; food intolerance, less so. Please respond with further questions or concerns if you wish.