Microbiology Case Study: A 62 Year Old Man with a Lung Mass

A 62 year old male without a significant past medical or smoking history was referred to pulmonology for an abnormal chest CT.  Three months prior to presentation, the patient had developed a cough after doing some home remodelling that involved sanding drywall.  The cough became severe and blood-tinged, including some clots, so the patient sought medical attention.  The patient denied any other symptoms and reported feeling well overall.  Physical exam findings were all within normal limits.  A chest X-ray showed a round lesion in the left lower lobe.  Follow-up chest X-rays showed that the lesion had decreased in prominence but had not resolved.  Subsequently, a chest CT was performed that showed a 2.8cm mass-like focal area of consolidation in the left lower lobe without associated lymphadenopathy.  Because malignancy could not be excluded, the patient underwent bronchoscopy with biopsies obtained for cytopathologic evaluation as well as mycobacterial and fungal cultures.

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Image 1: Cytologic preparation (alcohol-fixed, Papanicolaou-stained) of lung, left lower lobe, 2.8cm mass, fine needle aspiration.

The cytologic preparation of fluid from a fine needle aspiration (Image 1) shows granulomatous inflammation with patchy necrosis.  Typically, a mixed inflammatory reaction is observed, with neutrophils, granulomas, epithelioid histiocytes, and foreign body giant cells.  Examination reveals several round-to-oval yeast cells, measuring 9-13μm in diameter.  Single broad-based (4-5 μm wide) buds and thick, double contoured, refractile cell walls are also characteristic of the yeast forms visualized here, leading to a rapid presumptive diagnosis.

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Image 2: Scotch Tape touch preparation of one white colony growing on potato flake agar (25°C) after 10 days of incubation.

Growth of the fungus on various culture media is more sensitive than direct examination and yields a definitive diagnosis.  On potato flake agar incubated at room temperature (25°C), one white colony that was tan on the reverse began growing at 8 days.  Typically, colonies appear in 1-4 weeks and range from white (initially) to brown (with age).  Microscopic examination of a Scotch Tape touch prepared at 10 days (Image 2) demonstrates the mold form of this dimorphic fungus has delicate, septate hyphae with right-angle conidiophores that bear single, terminal conidia (resembling lollipops).  A DNA probe is used to confirm the identification of Blastomyces dermatitidis.

Discussion

As described above, Blastomyces dermatitidis is a thermally dimorphic fungus.  In the environment, the mold form of B. dermatitidis is found in wet soil, particularly when enriched by animal droppings and decaying organic matter (1).  When a susceptible host (healthy or immunocompromised) disrupts wet earth that contains B. dermatitidis, infectious conidia are inhaled into the lungs.  Adult men are more likely to have blastomycosis, likely because they partake in outdoor activities (ex. hunting, fishing) that are associated with environmental exposure to airborne conidia.

Symptoms of blastomycosis are variable, ranging from asymptomatic or transient flu-like to severe pulmonary involvement.  Patients may present with symptoms of acute pneumonia (fevers, chills, cough, hemoptysis, and dyspnea) that can be indistinguishable from viral or bacterial causes.  Other patients, with chronic pneumonia, have systemic symptoms (weight loss, low-grade fevers, night sweats, productive cough, and chest pain) that overlap with pulmonary tuberculosis, histoplasmosis, or bronchogenic malignancy.  In addition to the primary pulmonary infection, approximately half of patients develop extrapulmonary symptoms from hematogenous dissemination to almost any organ; most commonly to skin, bones, male genitourinary, and the central nervous system.

Regardless of symptoms, a majority of patients with blastomycosis will have chest X-ray findings, alveolar infiltrates or a mass lesion involving any location that are non-specific and may mimic malignancy.  The mortality rate is 0% in healthy hosts and up to 30% in immunocompromised people, frequently due to disseminated disease.  There are no guidelines for susceptibility testing of dimorphic fungi.  The preferred treatment of mild to moderate pulmonary blastomycosis is itraconazole for 6-12 months.  Conversely, amphotericin B is used in moderately severe disease to treat chronic pulmonary symptoms, disseminated blastomycosis, CNS involvement, immunocompromised or pregnant patients.

Reference

  1. Saccente M, Woods GL. Clinical and laboratory update on blastomycosis. Clin Microbiol Rev. 2010;23(2):367-81.

 

-Adina Bodolan, MD is a 1st year anatomic and clinical pathology resident at the University of Vermont Medical Center.

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-Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Associate Professor at the University of Vermont.

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