It was first described by Thomas Casper Gilchrist in 1894 and sometimes goes by the eponym Gilchrist's disease . It is also sometimes referred to as Chicago Disease.

Epidemiology

In the US:

Most cases of blastomycosis occur in the United States. It is endemic in the Mississippi river and Ohio river basins and around the Great Lakes. The annual incidence is less than 1 case per 100,000 people in Mississippi, Kentucky, Arkansas, and Wisconsin.

In Canada:

Most cases of blastomycosis in Canada occur in northwestern Ontario, in particular, around the Kenora area. The moist, acidic soil in the surrounding woodland harbours the fungus.

Internationally:

Blastomycosis is distributed throughout the world. Cases are sometimes reported from Africa.

Pathophysiology

Infection occurs by inhalation of the fungus from its natural soil habitat. Once inhaled in the lungs, they multiply and may disseminate through the blood and lymphatics to other organs, including the skin, bone, genitourinary tract, and brain. The incubation period is 30 to 100 days, although infection can be asymptomatic.

Features

Blastomycosis can present in one of the following ways:

a flulike illness with fever, chills, myalgia, headache, and a nonproductive cough which resolves within days.
an acute illness resembling bacterial pneumonia, with symptoms of high fever, chills, a productive cough, and pleuritic chest pain.
a chronic illness that mimics tuberculosis or lung cancer, with symptoms of low-grade fever, a productive cough, night sweats, and weight loss.
a fast, progressive, and severe disease that manifests as ARDS, with fever, shortness of breath, tachypnea, hypoxemia, and diffuse pulmonary infiltrates.
skin lesions, usually asymptomatic, appear as ulcerated lesions with small pustules at the margins
bone lytic lesions can cause bone or joint pain.
prostatitis may be asymptomatic or may cause pain on urinating.
laryngeal involvement causes hoarseness.

Diagnosis

Once suspected, the diagnosis of blastomycosis is confirmed by demonstration of the organism, usually in the sputum, by KOH prep, culture or DNA antibody test. Organisms can also be found in skin ulcers along the margins.

Treatment

Amphotericin B is the treatment of choice, is highly effective, but is quite toxic. In milder cases, itraconazole can be used.

Prognosis

Mortality rate in treated cases

0-2% in treated cases among immunocompetent patients
29% in immunocompromised patients
40% in the subgroup of patients with AIDS
68% in patients presenting as acute respiratory distress syndrome (ARDS)

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Pulmonary Blastomycosis: Diagnostic Techniques - Abstract
From CHEST, 10/1/00 by Marek A Martynowicz

Marek A Martynowicz, MD(*) and Udaya BS Prakash, MD. Pulmonary & Critical Care Medicine, Mayo Clinic & Foundation, Rochester, MN.

PURPOSE: To define clinical value and sensitivity of various techniques used for the diagnosis of pulmonary blastomycosis we 1) analyzed the use of specimens obtained from extrapulmonary sites, pulmonary specimens obtained non-invasively (sputum, gastric washings, tracheal secretions), and pulmonary specimens obtained invasively (bronchoscopy, transthoracic needle aspiration [TTNA], open lung biopsy [OLB]); and 2) compared diagnostic yields of the above techniques, including the analysis of specific bronchoscopic approaches (bronchial washings, bronchoalveolar lavage [BAL], protected speciment brush [PSB], bronchial brush, transbronchial biopsy [TBB], transbronchial needle aspiration [TBNA]).

METHODS: Retrospective chart review of all patients diagnosed with blastomycosis at the Mayo Clinic Rochester between 1967 and 1998.

RESULTS: 63 patients with pulmonary blastomyeosis were identified. In 8 patients (13%), diagnosis was based on Blastomyces dermatidis recovered from an extrapulmonary site (skin and bone in 5 and 3 patients, respectively) accompanied by a compatible chest radiograph. In 35 (56%) patients a pulmonary specimen obtained non-invasively provided the diagnosis (sputum, gastric washings and tracheal secretions in 25, 7 and 4 patients, respectively). In 20 patients (32%) a pulmonary specimen obtained invasively was the only source for the diagnosis (bronchoscopy, TTNA and OLB in 13, 1 and 6 patients, respectively). Diagnostic yield of the modalities used was as follows: sputum culture 25 of 28 (89%); gastric washings culture 7 of 8 (88%); tracheal secretions culture 4 of 5 (80%); bronchial washings 18 of 19 (95%); BAL 5 of 7 (71%); PSB 5 of 5 (100%); bronchial brush 2 of 8 (25%); TBB 4 of 10 (40%); TBNA 0 of 1 (0%); TTNA 1 of 3 (33%); OLB 11 of 12 (92%).

CONCLUSION: In majority of patients diagnosis of pulmonary blastomycosis was made without utilization of an invasive thoracic procedure (56%) or based on the recovery of B. dermatidis from an extrapulmonary site and compatible chest radiographs (13%). Among bronchoscopic procedures, yields of bronchial washings and PSB tended to be superior to BAL. Bronchoscopic cytological and histologic specimens had a poor diagnostic yield.

CLINICAL IMPLICATIONS: If pulmonary blastomyeosis is a clinical consideration sputum, gastric washings and/or tracheal secretions should be collected for cultures. If bronchoscopy is performed, bronchial washings and PSB are the preferred diagnostic specimens.

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