Page 410 - Problem-Based Feline Medicine

402 PART 7 SICK CAT WITH SPECIFIC SIGNS

Common localizing signs of infection include: ● Histoplasma capsulatum appears as numerous
● Respiratory signs, including nasal discharge small round yeasts with a dark center and surround-
(cryptococcosis), and dyspnea due to fungal pneu- ing halo inside macrophages.
monia; hilar lymphadenitis. More than 50% of cats
Serology is useful for identifying cryptococcosis, coc-
with histoplasmosis are dyspneic.
cidioidomycosis, blastomycosis and sporotrichosis.
● Lameness from bone or joint infection, especially
with coccidioidomycosis. Organisms can be cultured, but this requires special
● Skin lesions: nodules, ulcers and abscesses that media and biohazard containment.
have not resolved with typical wound treatment, i.e.
drainage, irrigation and antibiotic therapy. Skin
lesions are the salient feature of sporotrichosis.
● Neurologic signs, including seizures. Differential diagnosis
● Ocular signs, including uveitis and chorioretinitis.
Neoplasia – signs of neoplasia and systemic mycoses
Solitary, regional, generalized peripheral and inter- are similar because both are due to invasion and prolif-
nal lymphadenopathy may be present. Peripheral eration of eukaryotic cells.
lymphadenopathy is common with sporotrichosis.
Tuberculosis, nocardiosis and other chronic bacterial
infections.
Diagnosis
Differentiation is based on cytology, histology and
Exposure history is important for diagnosis. Endemic culture.
areas include: eastern North America (blastomycosis);
southwest North America, northern and south central
South America (coccidioidomycosis). Others are
Treatment
world-wide.
Itraconazole 5 mg/kg q 12 h for weeks to months is
Blastomycosis is uncommon in cats compared to dogs.
effective against most dimorphic fungi. Treat a mini-
Lymph node biopsy reveals hyperplasia or less com- mum of 30 days beyond clinical resolution. Amphotericin
monly lymphadenitis. B and liposomal-encapsulated amphotericin B are
alternate treatments. Ketoconazole may be substituted
Definitive diagnosis is by identification of the organ-
for itraconazole in some cases to reduce cost of therapy,
isms in biopsy specimens of affected tissues by cytol-
but is often less effective.
ogy or histology. Cytologically:
● Cryptococcus neoformans appears as large, encap- Fluconazole is the drug of choice for central nervous
sulated, narrow-based budding yeasts. With the system infections.
capsule most organisms are the same size or larger
Iodides are the older standard treatments for sporotri-
than surrounding inflammatory and epithelial cells.
chosis. Supersaturated solution of potassium iodide or
India ink stain helps identify the capsule.
20% sodium iodide may be used at a dose of 20 mg/kg
● Sporothrix schenkii appears as a cigar-shaped
PO once or twice daily, with food.
yeast inside macrophages.
● Blastomyces dermatitidis appears as broad-based Zoonotic potential:
budding yeasts, slightly larger than surrounding ● Sporothrix schenkii is highly contagious from
neutrophils. With new methylene blue stain the lesions.
organism has an obvious double wall and green ● Coccidioides immitis may revert from tissue yeast
tinge. phase to mycelial phase on bandage surfaces and
● Coccidioides immitis appears as solitary large non- release highly contagious arthrospores. Avoid
budding yeasts three times the size of surrounding bandaging wounds or change dressings fre-
neutrophils, but it is present in low numbers and quently.
hard to find. Other dimorphic fungi are not contagious.