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.


Skin. Dermatologic manifestations of blastomycosis occur in 30% to 50% of infected dogs. Granulomatous proliferative masslike lesions and ulcerated skin lesions draining serosanguineous or purulent fluid are most common.1-4,11 Skin lesions most commonly involve the nasal planum, face, and nail beds.1-3,14,15 A thorough examination of the skin is recommended in all dogs suspected of having blastomycosis, as aspirates or impression smears from seemingly insignificant skin lesions could yield a rapid diagnosis.

Bone. Solitary bone infections causing lameness occur in up to 30% of infected dogs,1-3 typically involving bones of the distal limbs. Radiographically, the fungal osteomyelitis lesions are osteolytic with periosteal proliferation and soft tissue swelling, requiring cytology or biopsy to distinguish between fungal and neoplastic disease.

Other sites. Tissues less commonly infected include the prostate, kidneys, testes, joints, nasal passages, and brain. Central nervous system (CNS) infections are identified in only 3% to 6% of cases.2,3,16,17 Reported neurologic findings include depressed mentation, lethargy, neck pain, circling, cranial nerve deficits, head pressing, seizures, hypermetria, ataxia, and tetraparesis.4,9,18,19 Dogs with CNS blastomycosis nearly always have clinically apparent involvement of extraneural sites, making diagnosis relatively straightforward.3,6,16,18,19

Laboratory findings

Mild normocytic, normochromic, nonregenerative anemia is common, as is moderate leukocytosis characterized by mature neutrophilia or neutrophilia with a left shift. Hypoalbuminemia (75% of cases) and hyperglobulinemia (50% of cases) also occur.1,3,20,21 Albumin, a negative acute phase protein, is frequently decreased with inflammatory conditions. Hypercalcemia has been identified in 2% to 10% of dogs with blastomycosis, perhaps related to active vitamin D production by stimulated macrophages.1,3,20,21

Thoracic radiography

Figure 2A. A lateral thoracic radiograph showing a diffuse miliary interstitial pattern in the lung of a dog with blastomycosis.
Perform a thoracic radiographic examination in all dogs with suspected blastomycosis, regardless of whether respiratory signs are evident.1 Diffuse miliary to nodular interstitial and bronchointerstitial pulmonary changes are most common (Figures 2A & 2B).22,23 Less often, lung lobe consolidation or a solitary mass within the lung parenchyma is identified (Figure 3).22 Hilar lymphadenopathy may occasionally be evident.1-4

Figure 2B. A ventrodorsal thoracic radiograph showing a diffuse miliary interstitial pattern in a dog with blastomycosis.
The lungs will appear normal radiographically in a few dogs with pulmonary parenchymal disease since inflammatory nodules smaller than 5 mm in diameter may not be detected.24,25 Obtain right and left lateral views and a ventrodorsal radiograph whenever possible in a stable patient to increase the likelihood of finding small lesions.26 Computed tomography is more accurate in detecting pulmonary nodules in people than radiography is and may be beneficial in dogs with subtle pulmonary lesions.25

Cytologic diagnosis

Figure 3. A lateral thoracic radiograph showing a focal granuloma (arrow) in the lung of a dog with blastomycosis.
Blastomycosis is most reliably diagnosed by demonstrating the organism in cytologic or histologic samples from infected tissues. Samples from infected sites usually show evidence of pyogranulomatous or purulent inflammation, which should prompt a careful search for yeast cells.11


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