Where to Start?

Pruritus in cats, like other species, can be caused by a multitude of diseases. Identifying the condition may be a frustrating process requiring a compliant and understanding pet owner. As with any dermatologic disease, a detailed history is essential before creating an appropriate list of differential diagnoses. A systematic diagnostic approach is necessary to avoid oversight of an important disease and should be performed on all cases. This should include the minimal database (MDB) of skin scrapings, fungal culture (DTM) and cytology. Further diagnostics are performed pending the history, clinical examination and differential diagnosis.

Examination should include detailed observation of lesions and distribution patterns. A general examination should also be included. Rule-outs should routinely be performed and therapeutic trials may be required. Perception of endemic diseases commonly seen in your geographic region should be prioritized. The history of the cat's current habitat and previous locations may be helpful and included in the history. Previous therapy and response should be acquired.

Clinical manifestations are variable in the pruritic cat. Presentations commonly seen include miliary dermatitis characterized by a papular–crusting dermatitis. The descriptive term meaning "seed-like" represents a wide variety of diseases and is only a reaction pattern of the skin. Feline symmetrical alopecia is another clinical presentation characterized, as the name implies, by a symmetrical pattern of hairloss. This is also a descriptive term and represents a number of disease possibilities. Hairloss in the cat is most commonly self-inflicted. The cause of the compulsive over grooming is most often the result of a pruritic condition although psychogenic hair pulling and excessive licking is observed.

Eosinophilic lesions are also observed in the pruritic cat. These have been commonly referred to as the "eosinophilic granuloma complex." While idiopathic hypereosinophilic syndromes exist, the most common association is hypersensitivity reactions. Some animals will present with regionalized or generalized dermatitis although when inflammation is present, papules and crusts are often observed with characteristic features of "miliary dermatitis." In other words, regionalized or generalized erythema without papules is rare.

Diseases To Consider In The Pruritic Cat

Hypersensitivity Reactions

Flea allergy dermatitis is probably the most common allergic condition observed in flea infested areas. This condition may be observed with the classical miliary dermatitis regionalized over the pelvic region. Caudal abdominal alopecia is often seen and a circumferential miliary dermatitis is observed around the neck.

Adverse reaction to food was considered to be a more common problem than recognized now. It is typically characterized by severe pruritus with excoriations and evidence of self mutilation. Miliary dermatitis, multifocal to symmetrical alopecia, eosinophilic ulcers or plaques and erythroderma may be seen. Facial pruritus is a hallmark of this problem.

Feline atopy is a pruritic disease of cats that is underestimated in frequency of occurrence. The characteristics are similar to those of adverse reaction to food ("food allergy") and may have an assortment of lesions. Pruritus may be seasonal or non-seasonal and does not require routine outdoor exposure. In fact, cats with restrictive inside habitats have been observed with seasonal pruritus and cats restricted inside have demonstrated reactivity to pollen aeroallergens through intradermal testing. Facial pruritus should elicit feline atopy as a differential. Symmetrical alopecia is frequently observed with common distribution in the medial aspect of the forelegs, caudal abdomen and lateral regions of the trunk. Otitis externa may be present and often complicated by yeast or bacterial infection. Eosinophilic lesions may be observed, particularly affecting the head and thorax. The age of onset for feline atopy is not as restrictive as canine atopy and may occur later in life beyond seven years of age. While canine atopy is usually steroid responsive, feline atopy may be refractory.

Insect hypersensitivity is often a component of feline atopy but may be observed as a separate entity. The allergens I include in this category are: cockroach, mosquito, house fly, deer fly, horse fly, moth, black ant, fire ant, etc. The clinical features may be similar to those observed for atopy. Steroid responsiveness may be limited and the condition may be generalized although the face and head are usually affected.