Page 630 - Small Animal Clinical Nutrition 5th Edition

652 Small Animal Clinical Nutrition

alter cell mediator production in canine mast cells (Gueck et al, lesions can usually be palpated over the dorsal lumbar and cer-
VetBooks.ir 2004). If similar changes occur in dermal mast cells from vical regions long before they are visualized. Feline miliary der-
matitis is most commonly a manifestation of flea allergy, but
patients with atopic dermatitis, these results suggest that GLA
and omega-3 fatty acid supplements or similarly enriched foods
may occur with other ectoparasite infestations, dermatophyto-
might be beneficial. Black currant oil, borage oil and evening sis, bacterial folliculitis, adverse food reactions, atopic dermati-
primrose oil are sources of GLA (Meydani et al, 1991; Calder tis, drug eruptions and immune-mediated skin disease.
et al, 1990; Endres et al, 1989, 1993; Baldie et al, 1993; Lee et Canine flea-bite hypersensitivity is characterized by a prurit-
al, 1985). ic, papular dermatitis (Scott et al, 2001). Flea bites induce an
Besides affecting LT and PG production, EFA exhibit initial papule that may then form a crust. Chronic pruritus may
numerous additional immunomodulating properties. They lead to alopecia, lichenification, severe crusting and hyperpig-
have been reported to decrease the synthesis of proinflammato- mentation. Lesions are typically confined to the dorsal lum-
ry cytokines, decrease T-cell lymphocyte proliferation and acti- bosacral area, caudomedial thighs, ventral abdomen and flanks.
vation, affect expression of cell adhesion molecules, influence Pyotraumatic dermatitis (“hot spots”), secondary bacterial pyo-
signaling within cells of the immune system and regulate cyto- derma and secondary seborrhea are common in chronic cases.
toxic activity of phagocytes by modulating the production of The presence of otitis externa, severe pedal pruritus or facial
reactive oxygen species (Olivry et al, 2001a). Preliminary inves- pruritus strongly suggests concurrent atopic dermatitis or ad-
tigations suggest that dogs with atopic dermatitis also may verse food reaction.
exhibit abnormal epidermal lipid levels and metabolism (Olivry Numerous insects besides fleas and arachnids in the normal
and Hill, 2001a). EFA have the potential to modulate this dog and cat environment can stimulate hypersensitivity reac-
abnormal skin lipid barrier function in animals with inflamma- tions. Blackfly, deerfly, horsefly, mosquito, red ant, black ant and
tory skin disease. tick bites may all contribute to allergic skin disease in dogs and
For more information about fatty acid metabolism and fatty cats (Griffin et al, 1993). The primary clinical sign is pruritus,
acid modulation of the inflammatory response see the Lipids although an erythematous maculopapular dermatitis may be
section in Chapter 5. present (Scott et al, 2001). Nodules and papules induced by
mosquito bites are usually found on the bridge of the nose and
Patient Assessment pinnae of cats. Stable flies occasionally induce a granulomatous
History and Physical Examination reaction, producing nodules or plaques and varying degrees of
Numerous skin diseases have an inflammatory component. alopecia on the pinnae. Ticks may induce nodules due to gran-
However, dietary fatty acid therapy has been used primarily in uloma formation at the site of attachment. Acute-onset nasal
patients with allergic skin disease or patients with pruritus or dermatitis has also been observed in dogs; pruritic papules and
papulocrustous dermatitis for which a specific cause has not nodules are found on the bridge of the nose.
been identified. Adverse reactions to food mimic other allergic diseases. The
Pruritus is the most common historical feature of allergic clinical features and management of adverse food reactions are
skin disease in dogs and cats. Clinical signs reportedly first described in detail in Chapter 31.
occur in most dogs and cats with atopic dermatitis between six
months and three years of age (Scott et al, 2001; Griffin et al, Laboratory and Other Clinical Information
1993; Griffin and DeBoer, 2001). Lesions of canine atopic der- Skin biopsy and histopathology can be used to confirm the
matitis usually involve the muzzle, periocular region, pinnae presence of inflammatory skin disease. Chronic hyperplastic
and external ear canals, paws, axillae, groin and abdomen. dermatitis is a common histopathologic reaction pattern seen in
Although the face and paws are most commonly involved, dogs with chronic allergy (Gross et al, 1992; Olivry and Hill,
many animals will have generalized pruritus by the time they 2001b).The predominant types of inflammatory cells may sug-
are examined. Chronic licking, rubbing, chewing or scratching gest the specific allergic disease. However, many chronic der-
can result in alopecia, lichenification, hyperpigmentation, scal- matoses have similar histopathologic features, making specific
ing and excoriation. Other common lesions in atopic dogs diagnosis difficult.The nature of epidermal and dermal inflam-
include papules and erythematous macules, secondary superfi- matory cell infiltrates in canine atopic dermatitis has recently
cial pyoderma, secondary Malassezia dermatitis, chronic otitis been characterized using modern immunologic techniques and
externa and seborrhea. is described in other sources (Olivry and Hill, 2001b).
Cats with atopic dermatitis most commonly exhibit symmet- Two methods of allergy testing are available to practitioners.
ric alopecia, miliary dermatitis, eosinophilic plaques, indolent Intradermal testing has been performed for many years. More
ulcer of the lip, pruritus of the head and neck with excoriations recently, in vitro tests for detection of allergen-specific IgE have
or generalized pruritus (Scott et al, 2001; Sousa, 1995). Atopic become commercially available.
cats are pruritic, but many are secretive and groom or traumatize Intradermal testing is widely used by veterinary dermatolo-
themselves without the owner’s knowledge. gists for making a definitive diagnosis of canine atopic disease
Cats with miliary dermatitis have numerous small erythema- and for selecting allergens for hyposensitization (Scott et al,
tous papules with adherent brownish crusts and various degrees 2001; Hillier and DeBoer, 2001). Intradermal allergy tests
of alopecia and pruritus (Scott et al, 2001; Sousa, 1995). These detect the allergen-specific IgE fixed to the surface of mast cells