Page 1438 - Clinical Small Animal Internal Medicine

1376 Section 12 Skin and Ear Diseases

and endocrinopathies. However, most diseases mani- pemphigus foliaceus and contact dermatitis tend to
VetBooks.ir fest between approximately 1 year and 6–8 years of age erupt rapidly. Cutaneous adverse food reaction may also
have a rapid onset, whereas endocrinopathies tend to
where no clear relationship between age and disease
exists. The breed of the patient may help with the devel-
not require a food elimination trial, as adverse food
opment of an initial differential diagnosis list. There are have a slow onset. A patient with seasonal pruritus would
some breeds, including those with a specific coat color, reactions cause year‐round signs.
that seem to be predisposed to specific dermatologic One of the most important historical questions to
conditions. In addition, certain diseases are congenital address is whether or not the disease was precipitated by
or have an identified heritable basis while others simply or associated with pruritus, as this information can rap-
occur more frequently in some breeds than in others idly help to generate and shorten the list of differentials.
(Table 157.1). If pruritus preceded the lesions, then allergic or parasitic
Occasionally, sex predilections for various diseases diseases are most likely. If lesions, such as alopecia, pre-
exist and can help in formulating and ranking the cede the pruritus, endocrinopathies, follicular dysplasias
differentials. For instance, females are anecdotally and follicular demodicosis must be explored. If papules,
reported to be more prone to systemic lupus erythema- pustules, epidermal collarettes or crusts precede the
tosus. Neuter status should also be taken into consid- pruritus, the so‐called “rash that itches,” pursue bacte-
eration. Estrus has been known to exacerbate pruritus rial, any nonpruritic dermatoses prone to developing
in females, and intact males are at increased risk for secondary bacterial infection such as endocrinopathies,
male feminization syndrome. and sterile pustular diseases (e.g., pemphigus foliaceus).
The disease history can be further clarified by address- Diseases that are typically or always pruritic include
ing some key questions including the date of onset (in atopic dermatitis, cutaneous adverse food reaction,
addition to the age of onset, discussed above), location flea bite allergy, contact hypersensitivity, sarcoptic and
and appearance of the initial lesions, duration and pro- notoedric mange, and demodicosis caused by Demodex
gression of the disease. The approximate date of onset gatoi in cats and Demodex cornei in dogs. Variably
may help to track seasonality or possibly create a time- pruritic conditions include cheyletiellosis, demodicosis
line for assessment of a drug‐ or vaccine‐induced cuta- caused by Demodex injai, Malassezia dermatitis, super-
neous reaction. Depending on geographic location, ficial pyoderma, feline dermatophytosis, autoimmune
disorders such as insect bite hypersensitivities and flea diseases such as pemphigus foliaceus, and epithelio-
allergy dermatitis tend to occur in the summer. In tem- tropic lymphoma. Diseases that are nonpruritic include
perate climates, atopic dermatitis often begins as a sea- endocrinopathies, follicular dysplasias, canine dermato-
sonal disease, typically worsening in the spring, summer, phytosis, and demodicosis caused by Demodex canis and
and/or fall. However, some patients with house dust Demodex cati. However, these conditions can be pruritic
mite hypersensitivity may worsen in the winter in addi- if accompanied by secondary infection.
tion to having year‐round pruritus. Canine flank alope- Identifying patterns of pruritus is also important for
cia, also known as seasonal or cyclical flank alopecia, identifying underlying disease triggers. A patient whose
tends to result in cyclical episodes of noninflammatory, pruritus always improves with a change in environment
nonpruritic alopecia in the winter where a shorter pho- likely has atopic or contact dermatitis. In a patient with
toperiod induces follicular arrest with resolution occur- nonseasonal pruritus that also has seasonal “flares,”
ring in the spring. adverse food reaction should be explored in addition to
Specifying the initial lesion location and pattern of dis- atopic dermatitis. A patient that suddenly becomes pru-
tribution can be extremely helpful in developing a dif- ritic after residing at a boarding kennel should be evalu-
ferential diagnosis list, as many diseases have distinct ated for sarcoptic mange.
areas of involvement. For instance, pemphigus foliaceus Owners often do not recognize the various manifesta-
affects the pinnae, dorsal aspect of the muzzle, and the tions of pruritus, such as licking, biting, chewing, rub-
pawpads. Sarcoptic mange tends to affect the pinnal bing, rolling, and scooting, and the clinician needs to ask
margins, elbows, and tibiotarsal areas. The importance about these variable signs. Therefore, evaluation of pru-
of lesional distribution will be further discussed in the ritus should not stop at asking if the patient “itches.”
physical exam (PE) section. Questions pertaining to dis- Also, determining the level of pruritus is important in
ease duration and progression should include if and how the development of an adequate treatment plan and eval-
location, appearance, and distribution have changed, uating the patient’s response to treatment. Commonly,
whether the onset was acute or slow and insidious, and if owners are asked to rank their pet’s level of pruritus on a
the disease is continuous or intermittent (seasonal or scale of 0 to 10, with 0 representing no itch at all and 10
nonseasonal). An acute onset of severe pruritus often being so itchy that the pet cannot sleep at night (and
occurs with sarcoptic mange, and diseases such as neither can the poor owner!).