AUTHOR AND EDITOR INFORMATION

Section 1 of 8  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Intervention
• Multimedia
• References

INTRODUCTION

Section 2 of 8  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Intervention
• Multimedia
• References

Background

Blastomyces dermatitidis is a thermally dimorphic fungus that causes the systemic pyogranulomatous disease termed blastomycosis. Blastomycosis is the least common of the endemic systemic mycoses; the other more common mycoses include histoplasmosis and coccidioidomycosis. Lungs, and to a lesser extent, skin and bone, are the most common organs involved with this fungus. Hematogenous dissemination can occur.

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Pathophysiology

Analysis of sporadic cases indicates that middle-aged men with outdoor occupations that exposed them to soil are at greatest risk for blastomycosis. Exposure to soil, whether at work or at play, appears to be the common link in reports of sporadic disease and outbreaks. The disease occurs more commonly in wooded areas and in hunters.

The respiratory system is considered the portal of infection. After inhalation of the conidia, neutrophils are the first cells recruited to the sites of infection, followed by lymphocytes. A reaction to the infection results in granuloma formation with central microabscesses (termed pyogranuloma) but does not result in caseation as occurs in histoplasmosis or tuberculosis. Cellular immunity is an important factor in defense against Blastomyces dermatitidis, but to a lesser extent than against other endemic mycoses. Infection is more extensive and outcome is worse in patients who are immunosuppressed or infected with HIV.

Frequency

United States

Endemic areas in North America include the southeastern and south central states, especially those bordering the Mississippi and Ohio river basins; the midwestern states and Canadian provinces (Quebec, Ontario, Manitoba) that border the Great Lakes; and a small area in New York and Canada along the St Lawrence River.

Most data are from Wisconsin, where the disease is a reportable condition. From 1986-1995, in a report by the Centers for Disease Control and Prevention, 670 cases were identified (mean annual incidence of 1.4 per 100,000).

International

Outside of North America, well-documented cases have been reported by Baily et al to occur most frequently in Africa. Occasional cases have been reported by DiSalvo to occur in Central America, South America, India, and the Middle East.

Mortality/Morbidity

Although the disease is relatively common, the exact mortality rate remains unknown. The case fatality rate reported to the Wisconsin Department of Health from 1986-1995 was 4.3% (29 of 670 patients). The disease is more aggressive in immunocompromised patients; in 1 series of these patients reported by Wheat, the mortality rate was approximately 30%.

Race

No racial predominance or seasonal predilection appears to exist for blastomycosis.

Sex

Men are affected more commonly with a male-to-female ratio of 3:2 in Wisconsin (1986-1995). In other series, it varies from approximately 5:1-15:1.

Age

Most patients are middle aged (mean age in Wisconsin data was 46 years). Although the disease is uncommon in children, a 1979 review of the literature documented 110 patients younger than 20 years.

Clinical Details

Infection commonly presents as a flulike illness associated with fever, cough, dyspnea, and pleuritic chest pain. Insidious weight loss, arthralgias, and myalgias are not uncommon, and erythema nodosum develops occasionally. The disease may affect only the pulmonary system or it can be extensively disseminated.

Pulmonary

Patients present with either 1) localized ill-defined lung opacity or a more discrete lung nodule or 2) with disseminated disease. Each manifestation occurs in approximately one half of patients. Disseminated pulmonary disease can be rapidly progressive and complicated by miliary (hematogenous) spread, leading to acute respiratory distress syndrome. A more indolent course clinically resembling tuberculosis can occur. The infection can be self-limited or chronic and progressive. Fibrosing mediastinitis and laryngeal, tracheal, and endobronchial invasion also have been reported.

Disseminated

Skin and bone lesions are the most common manifestations of disseminated disease (50% of patients). Skin lesions are as common as those found in the lung and tend to resemble neoplasms, both clinically and pathologically. Cutaneous disease appears similar to disease seen with pyoderma gangrenosum, leishmaniasis, Mycobacterium marinum infection, giant keratoacanthoma, and squamous cell carcinoma. Typical lesions are painless erythematous nodules that develop verrucous or ulcerative surfaces.

Bone and joint lesions occur in fewer than one half of patients with disseminated blastomycosis and are characterized by osteolysis. Involvement of the vertebrae can result in spinal cord compression.

The genitourinary system is involved in approximately 10% of male patients. Central nervous system impairment manifesting as meningitis, brain lesions, or epidural abscesses is relatively common (a minimum of 15% of patients).

Other rare sites of involvement include the eye, paranasal sinuses, pericardium, peritoneum, spleen, liver, adrenal gland, and thyroid.

Preferred Examination

Mycology

Diagnosis is based on demonstration of organisms in culture or on fungal stains (10% potassium hydroxide) of sputum, bronchoscopy specimens, or secretions obtained from cerebrospinal fluids or dermal, subcutaneous, or other lesions. Cultures are positive in more than 90% of patients. Culture growth may take from 1 to several weeks.

Radiologic modalities

Radiographic findings are nonspecific and variable. Chest radiography is the first imaging study performed. The most common pattern observed is acute nonspecific focal lung opacity, which is found in 25-75% of patients.

Limitations of Techniques

Radiographic patterns of pulmonary disease are indistinguishable from those of other mycotic infections.

DIFFERENTIALS

Section 3 of 8  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Intervention
• Multimedia
• References

Other Problems to be Considered

Mycobacterium tuberculosis
Nonmycobacterial tuberculosis
Miliary tuberculosis
Lymphoma
Bronchoalveolar carcinoma

RADIOGRAPH

Section 4 of 8  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Intervention
• Multimedia
• References

Findings

• Chest radiographs usually reveal focal lung opacities in the upper lobes (in 25-75% of patients), often nodular in character. In adults, the upper lobes are affected more frequently than the lower lobes with a ratio of approximately 2:1. In children, opacities most commonly involve the lower lobes. Lung opacities can be patchy or confluent and subsegmental, segmental, or nonsegmental (Picture 1, Picture 2). Radiographically, the appearance is similar to that seen with community acquired pneumonia, but slow improvement, lack of change, or even progression of disease over time should raise the possibility of granulomatous infection (Picture 3, Picture 4).
• The next most common radiographic presentation (in as many as 30% of patients) is a focal discrete mass, either single or multiple. The mass is usually well circumscribed, variable in size, and can occasionally contain air-bronchograms. When solitary, it can mimic primary carcinoma, especially when associated with unilateral lymph node enlargement or bone destruction (Picture 5, Picture 6).
• Cavitation occurs less commonly in patients with blastomycosis than in patients with tuberculosis or chronic histoplasmosis, with a reported incidence of approximately 15-20% (Picture 8, Picture 9).
• A minority of patients present with a miliary or diffuse interstitial disease pattern associated with respiratory failure and mechanical ventilation. This pattern can be observed in previously healthy immunocompromised patients as well. In many patients (as in Picture 10) the focal lung opacities or mass can be observed in association with the diffuse interstitial pattern, supporting the hypothesis of pulmonary dissemination from a focal pulmonary site.
• In contrast to histoplasmosis, hilar and mediastinal adenopathy and calcification are uncommon (10-20%) (Picture 10).
• Pleural involvement and significant effusion is uncommon (20%). Rarely, lung or pleural involvement can extend into adjacent bones or soft tissues. Pleural thickening without free effusion is a more common radiographic finding.
• Osteolytic lesions in the skeleton usually are associated with superficial abscesses.
• Rarely, mediastinal involvement results in superior vena cava obstruction or brachial plexopathy.

CT SCAN

Section 5 of 8  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Intervention
• Multimedia
• References

Findings

CT findings of pulmonary blastomycosis are variable. Similar to chest radiography, nonspecific lung parenchymal opacification is most commonly observed, followed by mass lesions (Picture 3, Picture 4). In a recent review of CT findings in 16 patients with pulmonary blastomycosis, Winer-Muram et al reported the following:

• A localized mass was observed in 14 patients (88%).
• Consolidation was observed in 9 patients (56%).
• Masses ranged from 3-16 cm in diameter (mean 8 cm).
• Most masses contained air bronchograms (12 of 14 patients or 86%) (Picture 7).
• In 11 patients, abnormalities were unilateral, and in 5, they involved both lungs.
• No lobar predominance was noted.
• Cavitation was observed in 2 patients (Picture 9), calcified hilar nodes in 7 (44%), and enlarged noncalcified nodes in 1 patient.

INTERVENTION

Section 6 of 8  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Intervention
• Multimedia
• References

Before the availability of chemotherapy for treatment of blastomycosis, the disease was reported to have a progressive course, with eventual extrapulmonary disease and a mortality rate exceeding 60%. Thus, after the introduction of effective antifungal therapy, it became accepted practice to treat all blastomycosis patients, especially those who are symptomatic.

Medical/Legal Pitfalls

• Failure to maintain a high index of suspicion resulting in misdiagnosis or delay in diagnosis. An inadequate review of the patient's occupation, travel history, and region of habitation may result in misdiagnosis. Because radiographic findings are nonspecific, the diagnosis commonly is delayed.
• Failure to initiate treatment promptly results in higher morbidity and mortality rates

MULTIMEDIA

Section 7 of 8  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Intervention
• Multimedia
• References

Media file 1:  A patient visited central Canada several months ago. He developed cough, fever, and dyspnea. Chest radiograph demonstrates focal patchy opacity in the lingula. Blastomyces dermatitidis was identified on bronchoscopy.
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Media file 2:  Lateral chest radiograph (same patient as in Picture 1) reveals the ill-defined lingular opacity and absence of pleural effusions.
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Media file 3:  A patient on mechanical ventilation because of acute respiratory distress secondary to diffuse blastomycosis. Bilateral pneumothoraces are the result of barotrauma. Right chest wall subcutaneous emphysema resulted from chest tube placement.
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Media type:  CT

Media file 4:  Chest CT image reveals patchy, dense lung opacification in the right middle and lower lobes. This is the most common presentation of blastomycosis. Lung opacities can be patchy or confluent and subsegmental or nonsegmental.
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Media type:  CT

Media file 5:  Chest radiograph demonstrates a spiculated mass overlying the left hilum. This radiographic finding mimics that of bronchogenic carcinoma, thus requires biopsy for tissue diagnosis.
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Media file 6:  Lateral chest radiograph (same patient as in Picture 5) reveals the central mass overlying the left hilum.
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Media file 7:  Chest radiograph from a patient with pulmonary blastomycosis demonstrates multiple nodular lesions, some of which are cavitating, in the left lower lobe. Cavitation occurs in 15-20% of patients with blastomycosis.
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Media file 8:  Chest CT (same patient as in Picture 7) reveals a thick wall cavity in the left lower lobe with surrounding focal parenchymal disease; needle biopsy of this lesion confirms blastomycosis. Cavitation occurs in 15-20% of patients with blastomycosis.
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Media type:  CT

Media file 9:  Chest radiograph from a patient with disseminated blastomycosis demonstrates diffuse miliary infiltrates associated with respiratory failure that required mechanical ventilation. This patient has right upper lobe dense opacification with cavitation. A diffuse micronodular pattern, occurring in a minority of patients, results from hematogenous spread of the disease.
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Media type:  X-RAY

Media file 10:  Chest radiograph from a patient with blastomycosis reveals left hilar lymphadenopathy, an uncommon finding in patients with blastomycosis.
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Media type:  X-RAY

REFERENCES

Section 8 of 8

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Intervention
• Multimedia
• References

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Article Last Updated: Aug 14, 2004