Page 607 - Cote clinical veterinary advisor dogs and cats 4th

Draining Tracts, Cutaneous 275.e3

out entirely because some pathogens are
fastidious and difficult to grow (e.g., L-form
VetBooks.ir • Routine CBC, serum biochemistry profile, Diseases and Disorders
infection of cats).
urinalysis: nonspecific
Advanced or Confirmatory Testing
• CT scan, MRI (p. 1132), or PET scan, often
with CT, can clarify the source and course
of a draining tract for surgical planning and
patterns consistent with foreign material or
neoplasia may be identified.
• Serologic testing for suspected infection (e.g.,
urine Blastomyces antigen test [p. 1365])
• Fundic exam
• Antinuclear antibody

TREATMENT
DRAINING TRACTS, CUTANEOUS Draining tract in a cat with panniculitis due to nocardiosis. (Courtesy Treatment Overview
Dr. Andrew Lowe.)
Varies widely, depending on the cause; more
specific treatment information may be sought
after this is determined.
Mycobacteria spp, L-form bacteria, deep bacte- of biopsy samples may also prove useful
rial infections and bacterial pseudomycetoma) (Diff-Quik followed by acid-fast and periodic Acute General Treatment
• Fungal and oomycotic infections (as above acid–Schiff staining; acid-fast staining is • In general, an inciting cause (e.g., foreign
plus zygomycosis, pythiosis, sporotrichosis, critical for identification of feline atypical body, neoplasm) should always be identified
and dermatophytic pseudomycetoma) mycobacterial infection or Nocardia infec- and, if present, removed for an optimal
• Parasitic (including leishmaniasis, neosporo- tion). If samples are submitted to an outside outcome/potential for cure. Surgical removal
sis, Cuterebra, dracunculiasis, and cutaneous laboratory, be sure to send unstained slides, of small bits of foreign material (e.g., grass
dirofilariasis) and advise the lab of differential diagnoses awns) can be challenging without advanced
Noninfectious causes: being considered. diagnostic imaging.
• Foreign bodies (although secondary bacterial • Diagnostic imaging/radiographs: may help • Lavage and debridement of the lesions in
infection is virtually inevitable) identify foreign bodies or diseases with combination with appropriate antimicrobial
• Immune-mediated (sterile nodular pannicu- systemic manifestations, such as pulmonary therapy based on culture and sensitivity are
litis, systemic lupus erythematosus, perianal involvement with blastomycosis or underly- indicated for infectious causes.
fistulae, drug eruption) ing bony lesions (e.g., osteomyelitis, neopla- • Noninfectious causes (e.g., sterile nodular
• Xanthomatosis sia). Fistulogram may be conducted with panniculitis, perianal fistulas) may respond to
• Neoplasia radiographic contrast to define the course immunosuppressive doses of glucocorticoids
of the tract before surgery. Ultrasound exam or other immunosuppressive therapies (e.g.,
DIAGNOSIS may identify foreign material not otherwise cyclosporine).
recognized on radiographic imaging.
Diagnostic Overview • Culture and sensitivity: bacterial (aerobic PROGNOSIS & OUTCOME
A draining cutaneous tract is a readily visible and anaerobic), fungal, and mycobacterial
but nonspecific clinical sign for which the cultures should be considered in cases of Varies, depending on the cause
underlying cause must be determined. Addi- persistent draining tracts. Culture of the
tional testing, usually beginning with cytologic superficial exudate will likely not reflect PEARLS & CONSIDERATIONS
evaluation of exudate, is almost always necessary. the true, deeper disease process. Samples of
Further tests are then indicated based on the deep tissue should be obtained by biopsy for Comments
cytologic results. culture. Many of the potential pathogens • Presence of Actinomyces often indicates that
are difficult to successfully culture (false- foreign material is present in the wound.
Differential Diagnosis negative results). Notify the laboratory about • Foreign body reactions are characterized
• Persistent exudation of fluid from subcutane- which differentials are being considered so by pyogranulomatous inflammation on
ous or deeper tissues through an opening in that appropriate sampling, transport, and histopathology.
the skin is characteristic of a draining tract. culture procedures are performed (many • Patients with chronic or recurrent infec-
• Few differential diagnoses exist; hemorrhage organisms are zoonotic under laboratory tious draining tracts should be evaluated
and serum exudation from a superficial conditions). for underlying immunosuppressive diseases
wound should be easily differentiated by • Histopathologic evaluation: obtain multiple or persistent local/focal abnormalities (e.g.,
nature of fluid and depth of wound. specimens from open and closed lesions. foreign body, neoplasm).
Wedge or elliptical biopsies provide a • Only after infectious agents have been
Initial Database better yield for deep subcutaneous lesions completely ruled out and a definitive diag-
A thorough diagnostic approach is indicated for than punch biopsies. Special stains may be nosis has been reached should treatment be
draining tracts. All of the following diagnostic required for positive identification (notify considered for noninfectious diseases that
tests are indicated for a complete evaluation. pathologist of differential diagnoses). respond to glucocorticoid therapy.
• Cytologic evaluation: the exudate and any • A lack of organisms on cytologic and
tissue granules should be crushed between histopathologic evaluation and culture, if Technician Tips
two slides and examined. Fine-needle performed correctly, may indicate a non- Patients with draining tracts should be handled
aspirates of nodules or impression smears infectious cause but does not rule infection with gloves, and contact with exudates should

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