A multitude of diseases can cause pruritus in the cat, from infectious diseases to allergic diseases to neoplasia. The degree
of pruritus also varies with the cause (Table 1).
Table 1: Feline skin diseases and degree of pruritus
Important information necessary to make a diagnosis can be found in the signalment, history, clinical signs, lesion location
and description, results of diagnostic tests, and in some cases response to therapy.
It can be difficult sometimes to know if a cat is pruritic. Some cats will present for "hair loss". If the cat only exhibits
pruritus in private, the owner will not know the cat is licking, scratching, or chewing on itself; however, if the hair shafts
are broken off, you can be sure the hair loss is a result of self trauma.
Important information to obtain from the history includes: family history of skin disease, age of onset of condition, severity
of pruritus, seasonality of pruritus, changes in degree of pruritus, location of pruritus, normal environment, changes in
environment, contact with other animals, whether other pets or people in household are affected, dietary history and any changes,
previous therapies and response, current medications, and description of lesions.
Physical examination should consist of a general physical exam as well as a thorough dermatologic exam. The general physical
examination may pick up signs of systemic disease that can affect the skin or that may make the skin disease irrelevant. The
dermatologic exam should note all primary and secondary lesions and their locations. Primary lesions include macules, papules,
pustules, furuncles, nodules, tumors, wheals, and vesicles. Secondary lesions include epidermal collarettes, scale, crusts,
erosions/ulcers, excoriations, scarring, lichenification, hyperpigmentation, comedones, and alopecia. Some of the dermatologic
abnormalities found may prompt a re-evaluation of the information obtained from the history. Many owners will not have noticed
ear, nailbed, or ventral tail lesions, especially if the patient is not very cooperative at home.
A differential diagnosis list will be formulated from the history and physical exam findings. Appropriate initial diagnostic
testing will then begin. Diagnostic tests may include superficial and deep skin scrapings, acetate tape preparations and combing
for parasites, hair plucks to look for broken hairs and/or parasites, skin surface cytology, fungal culture, flea combing,
skin biopsy, CBC, chemistry panel, urinalysis, thyroid evaluation, food trial, insect intradermal allergy testing, complete
intradermal/serum allergy testing, and trial therapy with lime sulfur dips.
A definitive diagnosis may be reached on the first or the fifth visit, and resolution or control of the condition may take
much longer. A logical, stepwise diagnostic and therapeutic plan will provide the clinician with the best chance of successfully
managing the patient.