Page 1445 - Clinical Small Animal Internal Medicine

157 Approach to the Patient with Dermatologic Disease 1383

Table 157.2 (Continued)
VetBooks.ir Lesion Definition

Fissure Linear cleavage in the skin
(see Figure 157.10)
Lichenification Thickening and hardening of the skin
(see Figure 157.11) characterized by an exaggeration of
the superficial skin markings.
Commonly hyperpigmented
Callus Alopecic, thickened, rough, often
lichenified plaque
Primary or secondary lesions
Alopecia Partial to complete loss of hair
(see Figure 157.12)
Scale Accumulation of loose fragments of
(see Figure 157.13) stratum corneum Figure 157.1 Macule – pigment changes occur due to increased
Crust Dried exudates of purulent material, or decreased melanin (inflammatory and noninflammatory
(see Figure 157.14) serum or blood on surface of skin causes), erythema or local hemorrhage. Other types of macules
include purpura, petechiae, and ecchymoses. Differential
Follicular casts Accumulation of follicular and diagnoses (DDx) – hyperpigmentation (noninflammatory): lentigo,
(see Figure 157.15) keratinaceous debris that adheres to pigmented nevi, endocrinopathies, hormonal diseases, color
multiple hair shafts at the level of the dilution alopecia and other follicular dysplastic diseases, such as
follicular ostia canine flank alopecia. Hyperpigmentation (inflammatory):
Comedones Dilated hair follicles filled with bacterial or yeast infections, dermatophytosis, parasitic disease,
(see Figure 157.16) cornified epithelium and debris and any disease resulting in pruritus. Depigmentation: vitiligo,
uveodermatologic syndrome, mucocutaneous pyoderma, discoid
Pigmentary Changes in skin coloration caused by a lupus erythematosus. Erythema: inflammation secondary to a
abnormalities variety of pigments (typically variety of underlying causes such as bacterial or yeast infections,
(see Figures 157.17 increased or decreased melanin) dermatophytosis, demodicosis, Sarcoptes, vasculitis, erythema
and 157.18) including black, blue, gray, tan, brown, multiforme, toxic epidermal necrolysis, pemphigus, cutaneous
as well as red/purple (hemorrhage T cell lymphoma, superficial necrolytic dermatitis (SND),
within skin) and yellow‐green (bile hypersensitivity disorders and solar dermatitis or hemorrhage due
pigment) to trauma, vasculopathies or coagulopathies. Photograph
illustrates lentigo.
Distribution of Lesions

In addition to recognizing lesion morphology, the location
and distribution must be identified. Lesion distribution
refers to whether the lesions are localized, multifocal,
regionalized or generalized, bilaterally symmetric versus
asymmetric, and identifying the general regions of the
patient that are involved. Bilaterally symmetric lesions
tend to occur in endocrinopathies, immune‐mediated and
autoimmune diseases, and can also occur in allergic skin
diseases. Asymmetric lesions are often the result of infec-
tious and parasitic disease processes. Certain diseases have
predilection sites for various areas of the body and famili-
arity with these regional characteristics is advantageous in
honing the list of differential diagnoses (Table 157.3).
Figure 157.2 Papule – these palpably solid elevations are usually
Dermatologic Diagnostic Tests pink to red in coloration and are caused by a localized
inflammatory cellular infiltrate within the dermis, epidermal
and Techniques hyperplasia, and early tissue infiltration of neoplastic cells.
DDx – superficial bacterial folliculitis, dermatophytosis,
After a list of differential diagnoses has been generated demodicosis, Sarcoptes, Cheyletiella, insect/arachnid
hypersensitivity, contact hypersensitivity, flea allergy dermatitis,
based on a thorough history and PE, diagnostic tests can atopic dermatitis, immune‐mediated disease, and drug reactions.
be employed to further narrow the list of differentials Photograph illustrates papules associated with sarcoptic mange.