Page 446 - Problem-Based Feline Medicine

438 PART 7 SICK CAT WITH SPECIFIC SIGNS

HISTOPLASMOSIS Diagnosis
Non-regenerative anemia is typically present and neu-
Classical signs trophilic leukocytosis. Severe pancytopenia is occa-
sionally observed when there is bone marrow
● Young, outdoor cats (< 4 years old).
involvement.
● Lethargy, anorexia and weight loss.
● Pale mucous membranes. Hyperproteinemia, hyperglobulinemia, +/− mild eleva-
● Mild to moderate respiratory signs (fever, tions of ALT may be observed.
dyspnea, tachypnea).
Radiographic imaging may aid diagnosis.
● Occurs in central United States.
● Survey thoracic radiographs show a diffuse pul-
monary interstitial pattern suggesting fungal pneu-
Pathogenesis monia.
● Symmetrical hepatomegaly is observed on survey
The etiologic agent is a soil-borne dimorphic fungus,
abdominal radiographs/ultrasonography.
Histoplasma capsulatum. The organism is likely
inhaled and disseminates from the respiratory tract to Definitive diagnosis requires demonstration of organ-
multiple other sites in the body (e.g. liver). isms in infected tissues.
● Potential diagnostic modalities include bron-
Granulomatous inflammation occurs in response to
choalveolar lavage, fine-needle aspiration and exfo-
fungal infection.
liative cytology, and tissue biopsy.
The disease is of regional significance in the central
Serologic tests for antibodies directed against
United States, especially the Mississippi and Ohio
Histoplasma antigens are not recommended, as false-
River Valleys and Texas.
negative results are common in cats with naturally
occurring disease.
Clinical signs
Differential diagnosis
Primarily disease of young (< 4 years of age) outdoor
Neoplasia and other systemic mycoses may produce
cats.
similar signs to histoplasmosis.
Cats present with a vague history of an insidious ● Cats with histoplasmosis (and other mycoses) tend
chronic illness. to be younger than cats with neoplasia.
● Serologic testing may be useful in detecting cats
Lethargy, anorexia, weight loss and pale mucous mem-
with cryptococcosis.
brane color are common.
Respiratory distress (dyspnea/tachypnea) is seen in Treatment
50% of infected cats and occasionally coughing.
Combination chemotherapy with amphotericin B and
Lymphadenopathy, splenomegaly and hepatomegaly itraconazole (5 mg/kg PO q 12 h), or high loading
are common. doses (10 mg/kg PO q 12–24 h) of itraconazole.

Mild to moderate fever is usually present, but the tem- Generally treat for 4–6 months but dependent on remis-
perature may be normal. sion of signs.
Intestinal involvement may result in diarrhea and weight See page 26 for details of amphotericin treatment in cats
loss. On palpation thickened intestinal loops, mesenteric (Cryptococcus in The Cat With Signs of Chronic Nasal
lymphadenopathy and/or hepato/splenomegaly may be Disease).
evident.
Prognosis
Ocular involvement may cause granulomatous chori-
oretinitis, retinal detachment with blindness and optic Fair to good with disseminated disease depending on
neuritis. the severity of fungal involvement and the chronicity.