Page 377 - Problem-Based Feline Medicine

19 – THE PYREXIC CAT 369

Cellulitis usually precedes an abscess, and if treated mycobacteria, and tumors. See page 1081, The Cat
appropriately, the abscess may not even form. With Non-Healing Wounds.
Cellulitis may be the only evidence of a previous
abscess.
Differential diagnoses
An abscess may rupture spontaneously, and the owner
In plague-endemic regions, Yersinia pestis (plague)
may notice foul-smelling, purulent discharge on the
must be considered, if the swelling is predominately
fur.
in the neck region and the cat’s fever is in the region of
● Some abscesses resolve on their own with or with-
40.5˚C (105˚F). Cautionary measures such as gloves,
out rupture, if they have been present long enough.
masks and isolation of the suspect cat should be taken
Regional lymphadenopathy may occur near the until diagnosis established. (See below for discussion
affected site. of Y. pestis infections).
L forms produce cellulitis 4–5 days after injury. Fracture.
Cellulitis spreads rapidly with the development of mul-
Ligament/tendon injury.
tiple fistulae and a febrile response.
● Lameness from septic arthritis is a common seque- Cellulitis.
lae to infection with L forms. Joints are affected by
Neoplasia.
the hematogenous route and may be distant to the
initial site. Lower limbs (tarsus and carpus) are
most commonly affected. The joints often ulcerate Treatment
with a grayish mucinous exudate. Infection remains
Clip area looking for evidence of puncture wounds.
confined to subcutaneous tissues and joints without
systemic spread to internal organs. Drainage of the purulent material is the key to treat-
ment. Surgical drainage can be done under sedation or
general anesthesia with a #15 blade. Make a 1/4–1/2"
incision over the dependent area, or the area most likely
Diagnosis
to allow for continued drainage.
History supports access to outdoors or conflict with
Flush the wound thoroughly with sterile saline or a
other cats indoors.
saline/betadine mixture.
Palpation reveals a tender area or fluctuant swelling,
Explore the wound with a sterile cotton swab or hemo-
with or without evidence of puncture wounds.
stats to assess the extent of dead-space and to look for
Microscopic examination of a fine-needle aspirate of a possible foreign body.
the abscess reveals a heterogeneous population of
Leave the wound open to allow drainage of further
bacteria, numerous degenerate neutrophils and intra-
purulent material. Do not suture incision closed, as this
cellular bacteria.
will only allow the abscess to reform. A Penrose drain
A complete blood count will generally show neu- may be placed for 2–3 days to allow maximum
trophilia. drainage for abscesses that close too early.
L forms are not visible in tissue samples even with spe- Antibiotic therapy for 7–10 days directed against
cial stains, nor do they grow on culture. On electromi- anaerobes: penicillins, cephalosporins, clindamycin and
croscopy, organisms are visible intracellularly within metronidazole are reasonable choices. Most abscesses
phagocytes. Diagnosis is often made by response to respond extremely well to drainage and amoxicillin at
tetracyclines in a therapeutic trial (doxycycline 10 10–20 mg/kg PO q 12 hours for 7 days or amoxi-
mg/kg PO, q 24 h). Response is rapid and evident cillin/clavulonic acid (12.5 mg/kg PO q 12 hours).
within 48 h.
L-forms and Mycoplasma spp. respond to doxycycline
Non-healing abscesses should have histopathology or tetracycline within 48 hours, but not other anti-
and culture of tissue. Causes include nocardia, fungi, biotics.