Page 1497 - Clinical Small Animal Internal Medicine

163 Approach to Alopecia 1435

gradually in the first three years of life (Figure 163.3). hypercortisolemia, hypothyroidism, hyperestrogenism,
VetBooks.ir The alopecia involves a defect in melanosome migration alopecia X, patterned alopecia of various breeds, cyclic
flank alopecia, postclipping alopecia, and anagen/telo-
and/or transfer, which occurs during the anagen phase of
gen defluxion. Some of these conditions are associated
the hair cycle.
with a temporary alopecia (postclipping alopecia, ana-
Alopecia Associated with Hair Cycle Arrest gen/telogen defluxion), some may be seasonal (cyclic
Alopecia associated with abnormal hair cycling typically flank alopecia), and others are likely permanent with
occurs because the hairs remain in telogen and a new variable response to treatments (alopecia X, patterned
anagen cycle is not initiated. With time, the telogen hairs alopecia). The cutaneous changes associated with endo-
are shed but are not replaced, resulting in a diffuse, often crine dermatoses may also occur with other hair cycle
symmetric alopecia. Areas of wear such as the neck, abnormalities, including diffuse alopecia often sparing
pressure points, and tail may become alopecic first as the head and distal extremities, seborrhea, comedones,
these hairs are removed by friction. hyperpigmentation, and cutaneous infections. In addi-
There are many conditions that appear to be associ- tion, many of the histologic characteristics associated
ated with hair cycle abnormalities. These include with endocrine dermatoses (telogen hairs, follicular ker-
atosis, hyperkeratosis, excess trichilemmal keratiniza-
tion [flame follicles], thin epidermis, and thin dermis)
may also be seen with other hair cycle abnormalities. It is
important to realize that, with a few exceptions, histopa-
thology cannot differentiate endocrine diseases from
other causes of hair cycle arrest.

Specific Noninflammatory Alopecic Disorders
Alopecia X
Alopecia X is a hair cycle arrest that affects primarily
plush‐coated breeds but also toy and miniature poodles
(Table 163.2). It is presumed to be hereditary because of
the strong breed predilections although the specific
defects or mode of inheritance have yet to be deter-
mined. Dogs affected are usually young adults but alope-
cia X can affect any dog between 1 and 10 years of age.
There is no sex or neuter status preference with this con-
dition. Clinically, dogs present with progressive symmet-
ric alopecia that spares the head and distal extremities
(Figure 163.4).
The alopecia is often associated with hyperpigmenta-
tion of the skin. Because of the similarity of this condi-
tion with endocrine dermatoses, it is important to rule
Figure 163.3 Neck region of a 9‐year‐old female spayed gray and those conditions out before a diagnosis of alopecia X can
white Italian greyhound with long‐standing color dilution
alopecia. The white hairs are normal. The area which had gray be made. A unique feature of this disease is hair regrowth
hairs is seborrheic and lichenified. at the site of biopsy or surgical trauma.

Table 163.2 Common breeds associated with noninflammatory alopecic syndromes (not inclusive)

Alopecia X Patterned alopecia Cyclic flank alopecia Color dilution alopecia Other

Chow chow American water spaniel Airedale Chihuahua (blue) Chesapeake Bay retriever
Keeshond Boston terrier Boxer Dachshund (blue) Labrador retriever (silver)
Malamute Dachshund English bulldog Doberman pinscher Schipperke
Pomeranian Greyhound French bulldog (blue and fawn)
Samoyed Irish water spaniel Weimaraner
Siberian husky Portuguese water dog Yorkshire terrier
Spitz
Toy/miniature poodle