Blastomycosis

BASIC INFORMATION
DEFINITION
Blastomycosis is a systemic pyogranulomatous infection, primarily involving the lungs, that arises after inhalation of the conidia of Blastomyces dermatitidis. Pulmonary blastomycosis varies from an asymptomatic infection to acute or chronic pneumonia. Hematogenous dissemination occurs frequently. Extrapulmonary disease of the skin, bones, and genitourinary system is common, but almost any organ can be infected.
EPIDEMIOLOGY & DEMOGRAPHICS
Most patients reside in the southeastern and south central states, especially those bordering the Mississippi and Ohio River valleys, the Midwestern states, and Canadian provinces bordering the Great Lakes. Rare cases have been reported outside the United States. Widely disseminated disease is most common in immunocompromised hosts, especially those with acquired immunodeficiency syndrome (AIDS).
PHYSICAL FINDINGS & CLINICAL PRESENTATION
• Acute infection: 55% symptomatic, median incubation 35 to 45 days, symptoms are nonspecific: mimic influenza or bacterial infection with abrupt onset of myalgias, arthralgias, chills and fever; transient pleuritic pain, cough that is initially nonproductive; resolution within 4 week is usual
• Chronic or recurrent infection: indolent and progressive; manifestations are diverse including pulmonary or extrapulmonary disease
Pulmonary manifestations: Symptoms and signs of chronic pneumonia: productive cough, hemoptysis, pleuritic chest pain, weight loss, low-grade pyrexia
Extrapulmonary manifestations:
1. Cutaneous: most common; may occur with or without pulmonary disease. Two different lesions:
Verrucous: beginning as a small papulopustular lesion on exposed body areas that may develop into an eschar with peripheral microabscesses
Ulcerative: Subcutaneous nodules (cold abscesses) may also occur.
2. Bone and joint: 12% to 50% of patients have osteolytic lesions; affects long bones, vertebrae, and ribs; lesions may present with a contiguous soft-tissue abscess or draining sinus that may spread to a joint resulting in a pyarthrosis
3. Genitourinary: 15% to 35% of patients; prostatic involvement is most common and may manifest as obstruction; epididymis and testes may also be affected.

4. Central nervous system: 5-6% normal host; 45% AIDS patients; meningitis and abscess formation

ETIOLOGY

B. dermatitidis exists in warm, moist soil that is rich in organic material. When these microfoci are disturbed, the aerosolized spores or conidia are inhaled into the

lungs. Disease at other sites is a result of dissemination from the initial pulmonary infection; the latter may be acute or chronic.

DIAGNOSIS

DIFFERENTIAL DIAGNOSIS

PULMONARY INFECTION:

• Tuberculosis

• Bronchogenic carcinoma

• Histoplasmosis

• Bacterial pneumonia

CUTANEOUS INFECTION:

• Bromoderma

• Pyoderma gangrenosum

• Mycobacterium marinum infection

• Squamous cell carcinoma

• Giant keratoacanthoma

WORKUP

• Physical examination and laboratory evaluation

• Definitive diagnosis established by culture

LABORATORY TESTS

• Presumptive diagnosis can be made by visualizing the distinctive yeast forms in clinical specimens.

• Culture: on Sabouraud’s or more enriched media

1. Aspirated material from abscesses

2. Skin scrapings

3. Prostatic secretions (urine culture with prostatic massage)

• Direct examination of clinical specimens

1. Wet preparation with 10-12% KOH

2. Histopathology: typically demonstrates pyogranulomas; yeast identification requires special stains

• Serologic tests: currently, a negative serologic test cannot be used to exclude blastomycosis, nor should a positive titer be an indication to start treatment.

IMAGING STUDIES

In chronic disease, chest radiographic findings are nonspecific but lobar or segmental alveolar infiltrates, especially of the upper lobes, are most common and may

progress to cavitation.

CLINICAL MANIFESTATIONS

Acute pulmonary infection is usually diagnosed in association with point-source outbreaks and is accompanied by the abrupt onset of fever, chills, pleuritic chest pain,

arthralgias, and myalgias. Cough is initially nonproductive but frequently becomes purulent as disease progresses. Chest radiographs usually reveal alveolar infiltrates

with consolidation. Pleural effusions and hilar adenopathy are uncommon. Most patients diagnosed with pulmonary blastomycosis have chronic indolent pneumonia

with signs and symptoms of fever, weight loss, productive cough, and hemoptysis. The most common radiologic findings are alveolar infiltrates with or without

cavitation, mass lesions that mimic bronchogenic carcinoma, and fibronodular infiltrates. Respiratory failure (adult respiratory distress syndrome) associated with

miliary disease or diffuse pulmonary infiltrates is more common among immunocompromised patients, especially those in the late stages of AIDS. Mortality rates are

≥ 50% among these patients, and most deaths occur within the first few days of therapy. Skin disease is the most common extrapulmonary manifestation of

blastomycosis. Two types of skin lesions occur: verrucous (more common) and ulcerative. Osteomyelitis is associated with as many as onefourth of B. dermatitidis

infections. The vertebrae, pelvis, sacrum, skull, ribs, or long bones are most frequently involved. Patients with B. dermatitidis osteomyelitis often present with

contiguous soft-tissue abscesses or chronic draining sinuses. In men, blastomycosis may involve the prostate and epididymis. Central nervous system (CNS) disease

occurs in < 7% of immunocompetent patients with blastomycosis. In AIDS patients, however, CNS disease has been reported in ~ 45% of cases, usually presenting

as a brain abscess. Less common forms of CNS disease are cranial or spinal epidural abscess and meningitis.

TREATMENT

ACUTE BLASTOMYCOSIS

• Indication for chemotherapy remains controversial in patients with acute pulmonary blastomycosis.

• Since the acute form may be benign and self-limited, patients may be closely observed.

• Some patients progress to chronic infection with attendant significant morbidity and therefore may require treatment.

• Patients who are immunocompromised, or have extrapulmonary disease or progressive pulmonary disease should be treated.