Page 1499 - Clinical Small Animal Internal Medicine

163 Approach to Alopecia 1437

Signalment
VetBooks.ir The breed and age of onset should aid in the initial dif-

ferential list (see Table 163.1). Congenital/hereditary alo-
pecias are more likely to occur within the first few years
of life while endocrine dermatoses and neoplastic dis-
eases occur in middle‐aged to older animals. Depending
on the trigger, immune‐mediated dermatoses can occur
within a wide age range and affect many breeds and their
crosses.

History and Clinical Signs

When evaluating the dog or cat for alopecia, a thorough
history and physical examination are in order.
Determining the presence or absence of pruritus and the
distribution and pattern of hair loss will help determine
the ultimate cause of the alopecia.
Clinically, pruritus‐induced alopecias are character-
Figure 163.7 Adult male castrated mastiff with postclipping ized by broken hairs where the animal has been
alopecia secondary to receiving an epidural injection.
scratching. Microscopic examination of the tips of the
hairs (trichogram) will show a blunted or fractured tip
is that the clipping/surgical preparation causes a hair instead of a tapered tip if the animal is inducing the
cycle arrest, possibly because of a temperature change alopecia secondary to trauma. This technique is not
with vasoconstriction to the skin surface. The other the- helpful if dogs are groomed and clipped regularly, as all
ory applies primarily to the plush‐coated breeds. It is of their hairs will be blunted. Evidence of excoriations
thought that these dogs may have been clipped during a supporting pruritus may also be observed in the alo-
time when their hair is in a prolonged telogen phase and pecic areas.
not able to initiate a new anagen cycle. It is also possible
that the clipping uncovered an endocrine or other non-
inflammatory alopecia condition. The hairs are not Onset of Alopecia
cycling because of an underlying disease such as hyper-
cortisolemia or alopecia X but alopecia has not yet If the onset of alopecia is rapid, infectious or paraneo-
occurred. The clipping simply hastened the alopecia. plastic conditions need to be considered. Also, a recent
With postclipping hair follicle arrest, the hairs should history of systemic illness could be the cause of a rapid
spontaneously resume normal cycling within 7–30 onset of alopecia.
months, often following a strong stimulus for hair cycling
such as shortening day length.
Ease of Epilation
Anagen/Telogen Defluxion Easy epilation of hairs is more often associated with
Anagen or telogen defluxion involves hair loss following inflammatory causes of alopecia such as pyoderma, der-
an illness. Telogen defluxion occurs more commonly in matophytosis or demodicosis but can also be seen with
small animals. The illness causes an abrupt cessation of conditions that result in rapid progression of alopecia
anagen, synchronizing all hairs in telogen. In 1–3 months such as anagen/telogen defluxion.
following the illness, large numbers of telogen hairs are
shed synchronously as a new anagen hair cycle begins.
Hairs epilate easily during this time. Anagen defluxion Distribution and Pattern of Alopecia
occurs more commonly in large animals. The illness
causes a generalized disturbance of the anagen stage of Distribution and pattern of the alopecia may be key to
the hair cycle resulting in a sudden loss of coat. In con- identifying the underlying diagnosis or formulating your
trast to telogen defluxion, hair loss occurs within two differential diagnosis list but requires careful observa-
days to one week following the illness. In both of these tion. If the alopecia is color restricted, likely this is color
conditions, hairs regrow normally. dilution alopecia or black hair follicular dysplasia. If the