Canine blastomycosis: A review and update on diagnosis and treatment - Veterinary Medicine
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Canine blastomycosis: A review and update on diagnosis and treatment
This fungal disease, which readily infects dogs and people, typically starts out in the lungs but can go on to invade many tissues throughout the body. Identifying it quickly and implementing antifungal therapy can result in a good prognosis.


Figure 4. Cytologic examination of a fine-needle aspirate from an enlarged lymph node in a dog with blastomycosis reveals Blastomyces organisms (Wright's-Giemsa stain).
Lymph nodes. Cytologic evaluation of fine-needle aspirates from enlarged, infected lymph nodes yields a diagnosis in 67% to 82% of cases (Figure 4).3,11 Aspirates from normal-size lymph nodes will also occasionally reveal organisms, so lymph node fine-needle aspiration is recommended in all dogs with suspected blastomycosis.24

Skin. When skin lesions are present, cytologic evaluation of exudates or aspirates from dermal lesions yields positive results in 85% to 94% of cases.3,11

Figure 5. Blastomyces organisms have been phagocytosed by macrophages in this transtracheal wash sample from a dog with pulmonary blastomycosis. Pyogranulomatous inflammation is evident (Wright's-Giemsa stain; 100X magnification).
Lungs. Cytologic examination of samples obtained from the lungs by transtracheal aspiration, bronchoalveolar lavage, and transthoracic lung aspiration has been evaluated in the diagnosis of pulmonary blastomycosis.9,10,27,28 Although early reports suggested that B. dermatitidis was not likely to be identified in transtracheal wash samples, two recent retrospective studies have demonstrated the organisms in 69% and 76% of transtracheal wash samples from dogs with radiographically evident pulmonary blastomycosis (Figure 5).9,27 Bronchoalveolar lavage yields similar results and generally superior sample cellularity than transtracheal wash does but requires general anesthesia.27 Transthoracic fine-needle aspiration of solitary or diffuse pulmonary lesions yields a diagnosis in about 80% of dogs with pulmonary blastomycosis but occasionally requires acquiring and evaluating multiple samples.10,28 The diagnostic utility of cytologic evaluation of respiratory samples obtained from patients with blastomycosis but without radiographically apparent lung disease has not been evaluated.

Figure 6. Cytologic examination of a vitreal aspirate from a dog with ocular blastomycosis reveals pyogranulomatous inflammation and Blastomyces organisms (Wright's-Giemsa stain; 50X).
Eyes. Most dogs with ocular blastomycosis have concurrent lung, skin, or lymph node involvement, allowing cytologic diagnosis to be made based on samples collected less invasively from these tissues. Vitreal aspirates and subretinal aspirates have been recommended in patients with only ocular involvement, but these techniques may threaten vision in an eye that is not already blind.1,11,12 Cytologic evaluation of vitreal aspirates resulted in organism identification in 100% of five cases in one report (Figure 6).3

CNS. Definitive diagnosis based on cerebrospinal fluid (CSF) analysis is rarely possible in dogs with blastomycosis involving the brain or spinal cord.16,18,19 Analysis of CSF from dogs with CNS blastomycosis typically reveals a lymphocytic to mixed pleocytosis, with a neutrophil concentration ranging from 5% to 40% of CSF leukocytes.16,18,29 But, occasionally, CSF will be normal or markedly neutrophilic.10 Blastomyces organisms are almost never identified in CSF.16,18,29 However, CNS blastomycosis rarely occurs in isolation, and cytologic identification of organisms in other infected tissues allows blastomycosis to be diagnosed.2,3,9,16,18,29


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