Signalment:
1 year old male domestic shorthair,
Felis domestics, feline.The cat presented with a 1month history of ataxia, head tilt, and aggression towards other animals and people. Prior to death, the cat was capable of eating and drinking.
Gross Description:
The animal presented in good body condition and postmortem preservation. The only significant
gross finding was a 1.2 cm in diameter well demarcated light brown mass in the rostral portion of the left cerebral hemisphere.
Histopathologic Description:
Located within the cerebral neuropil is an expansile, well demarcated area consisting of large numbers of neutrophils, macrophages, and lymphocytes, small amounts of fibrous connective tissue, and variably sized areas of necrosis. Intermixed throughout the lesion are low numbers of 7-2 micrometer round to oval yeast bodies which have thick cell walls, moderate amounts of poorly staining cytoplasm, and round 3-15 micrometer homologous staining nuclei. Some of the yeast bodies display broad based budding. Multiple blood vessels in the neuropil adjacent to the lesion are surrounded by low to moderate numbers of lymphocytes and macrophages. The overlying meninges contain low to moderate numbers of lymphocytes, macrophages and neutrophils, and small amounts of fibrillar acidophilic proteinaceous material.
Morphologic Diagnosis:
Severe chronic focal necrotizing pyogranulomatous encephalitis with intralesional yeast. Moderate chronic multifocal meningoencephalitis.
Lab Results:
Pathogenic bacteria, viruses, and fungi were not isolated from the brain, lungs, liver, kidneys, or intestines.
Condition:
Blastomyces dermatitidis
Contributor Comment:
Blastomycosis was diagnosed based on the morphological characteristics of the yeast.
Blastomycosis is most-frequently reported in canids and humans, though cases in other domesticated and non-domesticated species are occasionally seen(6). The dimorphic fungi are not commonly isolated from the environment, but are thought to survive in manure and in soil containing decaying vegetation and high moisture content(1). Disease is thought to be initiated by inhalation of
B. dermatitis conidia. At body temperatures, conidia transform to the yeast phase which may disseminate and elicit pyogranulomatous inflammatory responses in the lungs,
bones, liver, spleen, lymph nodes, skin, eyes, urogenital tract, and brain(2,4,7). This case is remarkable as the cat presented with neurologic signs accompanied with a distinct cerebral lesion suggestive of neoplasia. Lesions consistent with
B. dermatitis were not seen in other organs or tissues.
JPC Diagnosis:
Cerebrum: Meningoencephalitis, pyogranulomatous, multifocal, severe, with lymphocytic perivascular cuffing and budding yeasts.
Conference Comment:
The three clinical forms of blastomycosis are primary pulmonary infection, most common in domestic animals, disseminated disease, as in this case, and local cutaneous infection secondary to direct tissue inoculation, which is rare.
B. dermatitis has several virulence factors. Blastomyces Adhesion 1 (BAD-1) is a surface protein which mediates adhesion to host cells and modulates immune response, and alpha-glucan protects against killing by macrophages. The adhesion molecules bind to CD14 and complement receptor 3 (CR3) on macrophages and induces activation; however,
Blastomyces is not readily phagocytized.
Blastomyces initially causes a neutrophilic response, but with the onset of cell mediated immunity, a granulomatous response predominates. Differential diagnosis for this case includes
Cryptococcus spp., which often cause a gelatinous toruloma in the brain, and
Aspergillus spp., which often causes severe necrotizing vasculitis(3,5).
References:
1. Quinn PJ, Carter ME, Markey B, and Carter GP. Mycology. In: Veterinary Clinical Microbiology. 1999. Edinburgh. Mosby; 1994:367 -380.
2. Baumgardner DJ and Laundre B. Studies on the molecular ecology of
Blastomyces dermititidis. 2000. Mycopathol 152 5 1-58.
3. Hendrix DVH, Rohrbach BW, Bochsler PN, and English RV. Comparison of histologic lesions of endophthalmitis induced
Blastomyces dermititidis untreated and treated dogs: 36 cases (1986-2001). 2004. J Am Vet Med Assoc 224(8): 1317-1322.
4. Breider MA, Walker TL, Legendre AM, and van Ee RT. Blastomycosis in cats: Five cases (1979-1986). 1988. J Am Vet Med Assoc 193(5): 570-572.
5. van Ee RT and Wright B. Ocular changes in a cat with disseminated blastomycosis. 1985. J Am Vet Med Assoc 137(6): 629-631.
6. Caswell JL, Williams KJ. Respiratory System. In: Maxie MG, ed.
Jubb, Kennedy, and Palmers Pathology of Domestic Animals. Vol 2, 5th ed. Philadelphia, PA:Elsevier Saunders; 2007:640-4.
7. Lopez A. Respiratory system, mediastinum, and pleurae. In: McGavin MD, Zachary JF, eds.
Pathologic Basis of Veterinary Disease. 5th ed. St. Louis, MO:Mosby; 2011:526.
