A 4-year-old spayed female Domestic Shorthair cat present...

This is a classic and often frustrating presentation, Dr. [Referring DVM Name]. Chronic pruritus, multifocal alopecia, and miliary dermatitis in a cat, especially one unresponsive to glucocorticoids, strongly points towards an underlying allergic process. Your initial rule-outs of ectoparasites and dermatophytosis are excellent first steps, but let's ensure we've been truly exhaustive and then systematically tackle the allergic triad.

Re-evaluating Initial Rule-Outs

Ectoparasites (Revisited): While skin scrapes were negative, we must be absolutely certain about flea control.

Flea Allergy Dermatitis (FAD): This is the most common* cause of allergic skin disease in cats. Negative skin scrapes don't rule out fleas, especially in a fastidious groomer.
* Is the cat on a modern, highly effective isoxazoline (e.g., fluralaner, sarolaner, lotilaner)?
* Is it year-round?
* Are ALL animals in the household (dogs, other cats) on appropriate flea control?
* Is the environment being addressed?
My recommendation: Even if you think flea control is perfect, an empiric trial with a highly effective product (like fluralaner topical per label, q12 weeks) is warranted for 8-12 weeks, ensuring all animals are treated. This also covers Notoedres cati* (feline scabies), which causes severe head/neck pruritus and is rarely found on scrapes.
Ear Mites (Otodectes cynotis): If there's any* head or neck pruritus, ear cytology for mites is essential.

Dermatophytosis (Revisited): A negative fungal culture is reassuring, but ensure it was performed correctly (e.g., toothbrush technique, incubated for 3-4 weeks, proper interpretation of DTM color change and microscopic morphology). In multi-cat households, subclinical carriers are common.

The Next Crucial Step: Cytology

Before we proceed with allergy workups, we must rule out or treat any secondary infections. Cats can develop secondary bacterial pyoderma or Malassezia dermatitis, which will perpetuate pruritus.
Skin Impression Smears: Gently press a clean slide onto representative miliary lesions (after gently lifting any crusts) and any excoriated areas. Stain and examine for bacteria (cocci, rods), yeast (Malassezia*), and inflammatory cells (neutrophils, eosinophils).
* Ear Cytology: If there's any ear involvement, always perform ear cytology.

If secondary infections are present, treat them appropriately (e.g., topical chlorhexidine/miconazole shampoos/mousses, or systemic antibiotics like cephalexin 22-30 mg/kg PO every 12 hours for bacterial pyoderma, or itraconazole 5 mg/kg PO daily for yeast, given with food). You cannot accurately assess underlying pruritus until infections are resolved.

Systematic Approach to Feline Allergic Dermatitis

Once ectoparasites and dermatophytosis are confidently ruled out, and any secondary infections are resolved, we focus on the "Big Three" allergic causes in cats:

Cutaneous Adverse Food Reaction (CAFR):

Elimination Diet Trial: This is the only* way to definitively diagnose or rule out CAFR. Serum or saliva "food allergy tests" are unreliable and should not be used.
Diet Selection: Choose a novel protein diet (e.g., rabbit, duck, venison, insect-based) that the cat has never* eaten before, or a hydrolyzed protein diet.
* Duration: A minimum of 8 weeks, ideally 10-12 weeks, is required.
* Strictness: This is paramount. NO treats, NO table scraps, NO flavored medications (e.g., flavored heartworm prevention, flavored antibiotics), NO access to other pets' food, and absolutely NO hunting (if outdoor). This is often the hardest part for owners, but success hinges on it.
* Monitoring: Keep a pruritus diary. If pruritus resolves, challenge with the old diet to confirm the diagnosis.
My recommendation:* Begin a strict 8-12 week elimination diet trial immediately following resolution of any secondary infections.

Feline Atopic Dermatitis (FAD, environmental allergies):

* If the cat remains pruritic after a strict, successful elimination diet trial and optimal flea control, then FAD is the likely diagnosis (diagnosis by exclusion).
Allergy Testing: Intradermal allergy testing (IDAT) or serum IgE testing can be performed to identify specific environmental allergens. However, these tests are used to formulate allergen-specific immunotherapy (ASIT), not* to diagnose atopy. A cat can have FAD with negative allergy tests.
* Management Options:
* Allergen-Specific Immunotherapy (ASIT): This is the only treatment that can modify the disease course. It takes 6-12 months to see full effect.
* Cyclosporine (Atopica): An effective immunomodulator. Dose: cyclosporine 7 mg/kg PO daily. Monitor FeLV/FIV/Toxo status before starting. GI upset is common initially; giving it with a small meal or freezing the capsule can help.
* Glucocorticoids: Given the cat's unresponsiveness, this suggests either the previous dose was insufficient, the wrong type (prednisone vs. prednisolone), or underlying infections/parasites were still active. If needed, prednisolone (not prednisone in cats) 1-2 mg/kg/day can be used for flares, but long-term use carries risks (diabetes, skin fragility syndrome).

Summary of Next Steps

After confirming strict flea control and treating any secondary infections identified by cytology:

Initiate a strict 8-12 week elimination diet trial with a novel protein or hydrolyzed diet. Educate the owner thoroughly on the absolute necessity of strictness.

Monitor closely for reduction in pruritus and resolution of lesions.

If the cat remains pruritic despite a strict and adequate diet trial, then feline atopic dermatitis is the most likely diagnosis. At this point, discuss allergy testing for ASIT or long-term medical management with cyclosporine or careful use of prednisolone.

This methodical approach will help us pinpoint the underlying cause and develop a sustainable long-term management plan for this cat. Please send me photos of the current lesions and any cytology slides you obtain!