Diagnostics and Therapy in Veterinary Dermatology. Группа авторов

examined. Both the dorsal and palmar/plantar surfaces of each paw, as well as all interdigital spaces, should be evaluated for signs such as erythema, exudate, erosions, or draining tracts. The nails themselves may be misshapen, brittle, broken, soft, or discolored. Hair may need to be gently moved away from nailbeds/claw folds to allow complete visualization. Examination of the paw pads for hyperkeratosis, ulcerations, and other changes should also be performed (Figure 2.4).

      On the dorsal trunk, the general condition of the hair coat can be noted from a distance. Changes in texture, color, greasiness, or thickness can be observed. The hairs themselves should be parted to evaluate the skin surface for any papules, pustules, erythema, scaling, crusting, or other changes. The location of these changes should also be recorded (e.g. tail head, flank). The tail itself should also be evaluated, especially on the tip and in the area of the tail gland.

Ventrally, both axillae should be examined, and any erythema, moisture, or other lesions should be noted. The inguinal region and ventral chest are prone to lesions from bacterial infections that can be missed if the patient is not rolled over (Figure 2.5). This position can also be helpful for evaluating the perianal area, perivulvar fold, and prepuce. Nipples and mammary glands should be examined for subtle signs such as enlargement, discharge, or crusting.

Otoscopic evaluation should be performed in every patient, but can be delayed until the end of the exam as it can distress some animals. The pinnae themselves should be examined, with a focus on the concave aspect as well as the vertical canal. Lesions can be subtle in some cases, such as crusting on the pinnal margins associated with vasculitis (Figure 2.6). A handheld or video otoscope will usually allow visualization of the horizontal canal and tympanic membrane.

Figure 2.4 Hyperkeratosis, crusting, and erythema of the paw pads of a dog.

Figure 2.5 Epidermal collarettes, pustules, erythema, and hyperpigmentation on the abdomen of a dog with a bacterial pyoderma. These lesions were not visible until the dog was lifted for evaluation of the ventrum.

Figure 2.6 Alopecia, crusting, and hyperpigmentation along the pinnal margin in a dog with vasculitis.

      Primary and Secondary Lesions

      Differentiating between primary and secondary lesions can help develop the differential diagnosis list. Primary lesions develop spontaneously as a direct result of the underlying disease. The following are primary lesions:

       Papule: elevated domed skin lesion <1 cm

       Plaque: elevated skin lesion with a flat top >1 cm

       Nodule: elevated domed skin lesion >1 cm that is solid and typically extends to deeper skin layers

       Pustule: small, circumscribed elevation of skin containing pus

       Vesicle: circumscribed elevation of skin filled with fluid <1 cm

       Bulla: circumscribed elevation of skin filled with fluid >1 cm

       Macule: flat, distinct area of color change <1 cm

       Patch: flat area of color change >1 cm

       Wheal: elevation (often sharp) of the skin surface consisting of edema

       Cyst: membranous cavity or sac containing fluid or solid material

      Secondary lesions can develop from primary lesions or evolve from patient/external factors (such as medications or scratching). They can be helpful, as they may indicate primary lesions that are no longer present, e.g. ulcer developing from vesicle or bulla. The following are secondary lesions:

       Epidermal collarette: circular ring of crust or scale (may be secondary to a pustule or new evidence suggests some may be primary lesions)

       Lichenification: hardened, thickened skin that is often a response to chronic inflammation or friction

       Erosion: epidermal defect that does not penetrate the basal laminar zone

       Ulcer: epidermal defect that exposes underlying dermis (deeper than erosion)

       Excoriation: erosion/ulcer caused by scratching (often linear), rubbing, or biting

       Fissure: cleavage into epidermis or dermis

       Callus: thickened, hyperkeratotic, alopecic plaque

       Scar: fibrous tissue that has replaced damaged dermis or subcutaneous tissue

      Some lesions can be either primary or secondary. For instance, alopecia is a primary lesion in cases of hypothyroidism, but is secondary when caused by scratching. The following are primary or secondary lesions:

       Alopecia: loss of hair

       Comedo: hair follicle that is dilated and filled with sebaceous material and cornified cells

       Follicular casts: keratin and follicular material accumulation that adheres to hair shaft and extends beyond the surface of the follicular ostia

       Crust: dried exudate, serum, cells, blood, pus, and other materials adhered to skin

       Scale: loose fragments of cornified cells that accumulate on the skin surface

       Hyperpigmentation: darkening of skin color

       Hypopigmentation: lightening of skin color

      Lesion Distribution

In addition to lesion type, distribution on the patient’s body contributes to differential diagnosis list formation. For example, pustules and crusts present on the face, ears, and limbs of a dog are suggestive of pemphigus foliaceus. Erosions, ulcerations and draining tracts in the inguinal region of an overweight cat suggest infection with rapid‐growing mycobacteria (Figure 2.7). Feline mosquito bite hypersensitivity is characterized by papules, plaques, and crusts on the bridge of the nose, pinnae, and paw pads. Perianal erythema can be a sign of food allergy (Figure 2.8).

In addition to anatomic location, lesion distribution on different colors of the coat or skin can be important. These changes are often more subtle and can take practice to recognize. In cases of solar dermatitis, affected areas of white skin will be thickened, erythematous, and even infected, while adjacent pigmented skin will be normal (Figure 2.9). In cases of black hair follicular dysplasia, diffuse alopecia and broken hairs will be seen in black‐haired areas, while white‐haired areas will be normal.