Blastomycosis

Introduction 

Blastomycosis is a fungal infection caused by inhaling Blastomyces dermatitidis

-B. dermatitidis is a dimorphic fungus that exists as a mold in soil and as a yeast in tissue

-In the United States, it is endemic in the states bordering the Great Lakes and in the Mississippi River basin

-Its geographic location is similar to that of histoplasmosis 

-in soil it forms hyphae with small pear-shaped conidia

-Infections occur from inhalation of aerosolized conidia, which transform to the yeast phase in the lungs 

Symptoms & Signs 

-The most common sites of involvement in blastomycosis are lung, skin, bone, genitourinary tract, and central nervous system

Lungs: chief sites of involvement; may cause lobar pneumonia indistinguishable from bacterial pneumonia; fever, chills, cough, chest pain, and dyspnea 

Skin: the most common extrapulmonary form of blastomycosis; either verrucous or ulcerated in appearance

Bone: osteomyelitis frequently affecting the ribs and vertebrae 

Genitourinary tract:  causes epididymitis, prostatitis, and urethritis

CNS: causes meningitis, mass lesions, or brain abscess

Diagnosis 

Histology:  Rounded, double walled, spherical cells with broad-based buds (Cryptococcus neoformans forms a narrow-based bud)

Culture: most reliable; Hyaline branching septate hyphae with small pear-shaped conidia

Serology: detects Blastomyces antigen in urine and serum 

Imaging: Lobar consolidation on CXR or CT Chest

Treatment 

Itraconazole (the drug of choice), Voriconazole, Posaconazole, and Amphotericin B