Blastomycosis

Endemic mycoses in children in North America: a review of radiologic findings

Clinically significant endemic mycoses (fungal infections) in the United States (U.S.) include Blastomyces dermatitidis, Histoplasma capsulatum, and Coccidioides immitis/posadasii. While the majority of infections go clinically unnoticed, symptomatic disease can occur in immunocompromised or hospitalized patients, and occasionally in immune-competent individuals. Clinical manifestations vary widely and their diagnosis may require fungal culture, making the rapid diagnosis a challenge. Imaging can be helpful in making a clinical diagnosis prior to laboratory confirmation, as well as assist in characterizing disease extent and severity. In this review, we discuss the three major endemic fungal infections that occur in the U.S., including mycology, epidemiology, clinical presentations, and typical imaging features with an emphasis on the pediatric population.

Blastomycosis-Some Progress but Still Much to Learn

Blastomycosis, caused by Blastomyces spp., is an endemic mycosis capable of causing significant disease throughout the body. Higher rates of infection are seen in the Mississippi and Ohio River valleys, the Great Lakes region of the United States and Canada, much of Africa, and, to a lesser extent, in India and the Middle East. Limited reporting inhibits our true understanding of the geographic distribution of blastomycosis. An estimated 50% of those infected remain asymptomatic. Of those who present with symptomatic disease, pulmonary involvement is most common, while the most common extrapulmonary sites are the skin, bones, genitourinary system, and central nervous system. Itraconazole is the standard therapy for mild-moderate disease. Data for other azoles are limited. Amphotericin is used for severe disease, and corticosteroids are occasionally used in severe disease, but evidence for this practice is limited. Despite increasing incidence and geographic reach in recent years, there are still significant knowledge gaps in our understanding of blastomycosis. Here, we provide an updated review of the epidemiology, clinical presentations, and diagnostic and therapeutic approaches for this infection. We also discuss areas needing further research.

Imaging Manifestations of Blastomycosis: A Pulmonary Infection with Potential Dissemination

Pulmonary blastomycosis is an uncommon pathologic condition that is endemic to Canada and the upper Midwest of the United States. Blastomycosis has a variety of radiologic manifestations, including airspace consolidation, focal masses, intermediate-sized nodules, interstitial disease, miliary disease, and cavitary lesions. Affected patients may be asymptomatic or may present with clinical manifestations ranging from mild chronic cough to acute respiratory distress syndrome-like symptoms. Patients with acute symptoms are more likely to have airspace consolidation, whereas chronic manifestations may be associated with masslike lesions. Intermediate-sized nodules with accompanying airspace consolidation, particularly in the upper lobes, should raise suspicion for fungal disease. Lymphadenopathy and pleural effusions are quite uncommon, and calcification is not often seen. Blastomycosis may be aggressive and require treatment. Dissemination from the lung is not unusual and can involve any organ. Diagnosis is often delayed because blastomycosis can mimic many other disease processes, including bacterial pneumonia, malignancy, and tuberculosis. Radiologists can best contribute to the care of patients who live or travel in endemic areas by maintaining a high degree of suspicion for blastomycosis and being familiar with its myriad manifestations.

Paradise -- not without its plagues: overwhelming Blastomycosis pneumonia after visit to lakeside cottages in Northeastern Ontario

Background

Visiting lakes and cottages is a common leisure activity during summer among most Canadians and paradise for some. Various leisure activities are involved during these visits, including cleaning and 'airing' the cottage after long-winters, activities at the lakes and dock building etc, exposing the Canadians to moist soil and decaying woods – a source of white or tan mould – Blastomyces dermatitidis that may cause a flu-like illness to severe pneumonia that often remains a diagnostic challenge and results in delay in diagnosis and appropriate treatment thereby increasing associated morbidity and mortality.

Case Presentations

Five cases of overwhelming acute blastomycosis pneumonia are presented. Four of the five patients presented within few weeks of their visit to the cottages and surrounding lakes and all were initially treated as "community acquired pneumonia" that resulted in delay in diagnosis and poor outcome in the first patient. The first case, however, taught an important lesson that led to high-index of suspicion in the others with early diagnosis and improved outcomes. Interestingly, all patients were obese and had a shorter incubation period and severe clinical course. The possible mechanism for early and severe disease in association with obesity is speculated and literature is reviewed.

Conclusion

High-index of suspicion is important in the early diagnosis and appropriate management acute blastomycosis pneumonia to improve associated morbidity and mortality.

Meningoencephalitis due to Blastomyces dermatitidis: case report and literature review

Infection of the central nervous system by Blastomyces dermatitidis is a rare cause of meningoencephalitis. The existence of exclusive clinical infection of the meninges in the absence of pulmonary or other foci of infection has been debated. We describe a 20-year-old man presenting with meningoencephalitis caused by B dermatitidis. Blastomycotic infection was confirmed by isolation of the organism from brain tissue obtained at biopsy. Magnetic resonance imaging demonstrated progressive enhancement of basal meninges with involvement of bilateral basal ganglia and thalami. Treatment with amphotericin B arrested further neurologic decline. However, clinical and radiographic follow-up suggested damage to diencephalic structures. The diagnosis of blastomycotic meningoencephalitis is difficult to establish because no sensitive serologic test exists, and attempts to isolate the organism in cerebrospinal fluid obtained by lumbar puncture generally fail. A biopsy specimen of brain tissue is frequently necessary for the diagnosis. Survival is possible with timely initiation of therapy.

Disseminated blastomycosis in a rhesus monkey (Macaca mulatta)

An 8-year-old male rhesus monkey (Macaca mulatta) died following a 6-day illness consisting of progressive depression, anorexia, labored abdominal breathing, coughing, and tachypnea. Gross necropsy findings included severe multifocal (miliary) granulomatous pneumonia, granulomatous splenitis, and multifocal cerebral abscesses. Histologic examination revealed 10-15-microm broad-based budding organisms within pyogranulomatous inflammatory lesions in the lung, tracheobronchial lymph node, brain, spleen, and liver. The distribution of extrapulmonary lesions was intermediate between that described for dogs and that described for humans. These findings were consistent with blastomycosis, which is previously unreported in nonhuman primates.