Page 1449 - Clinical Small Animal Internal Medicine

157 Approach to the Patient with Dermatologic Disease 1387

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Figure 157.17 Pigmentary abnormalities – hypopigmentation‐
hypomelanosis occurs due to a loss of epidermal melanin.
DDx – primary: vitiligo. Secondary: common postinflammatory
change. Photograph illustrates depigmentation of the nasal
planum, rostral muzzle, and lips of a dog with vitiligo.

Figure 157.15 Follicular casts – these lesions are composed of a
combination of keratin and follicular material that adheres to the
hair shaft(s), extending above the surface of the follicular ostia.
DDx – primary: sebaceous adenitis, vitamin A‐responsive
dermatosis, idiopathic seborrhea. Secondary: dermatophytosis
and demodicosis. Photograph illustrates clumps of
keratosebaceous material adhered to the base of multiple hairs
from a dog with sebaceous adenitis.

Figure 157.18 Pigmentary abnormalities – hyperpigmentation‐
hypermelanosis occurs with increased epidermal and/or dermal
melanin. DDx – primary: endocrinopathies. Secondary: commonly
seen in chronic inflammation and as a postinflammatory change
associated with a variety of dermatopathies. Photograph
illustrates postinflammatory hyperpigmentation in a dog with
rabies vaccine‐induced alopecia.

Impression Smear
A routine impression smear is one of the most com-
monly employed dermatologic tests, and an excellent
technique to use when pustules, crusts, epidermal col-
larettes, and draining nodules are present and for moist
or greasy areas of the skin. When a pustule is present,
Figure 157.16 Comedones – in general, these lesions may form as gently “open” the pustule by using a 25 gauge needle and
a result of primary keratinization disorders or hyperkeratosis due pass it in a parallel fashion through the tip of the pus-
to endocrine abnormalities or inflammation. DDx – primary:
endocrinopathies, feline acne, some primary idiopathic tule. Avoid directly “poking” or “sticking” the pustule, as
seborrheas, congenital hypotrichosis (e.g., Chinese crested dogs), this will artefactually contaminate the specimen with
schnauzer comedo syndrome, and vitamin A‐responsive blood and blood‐associated leukocytes. When crusts
dermatosis. Secondary: seborrheic skin disease, application of are present, gently remove the crust and sample the con-
occlusive greasy medications and administration of systemic or tents underneath by pressing the slide gently onto the
topical corticosteroids, demodicosis and, less commonly,
dermatophytosis. Photograph illustrates comedones on the affected skin. This helps to avoid surface contaminants.
caudolateral aspect of the dorsum of a dog. When epidermal collarettes are present, rather than