A 48-year-old man comes to the physician with a 6-month history of cough and fatigue. He also has experienced malaise and weight loss. He does not recall any sick contacts. The patient is a carpenter. He smokes 1 pack of cigarettes daily. Temperature is 37.1 C (98.8 F). Examination shows left lower lobe crackles. HIV testing is negative. Chest x-ray reveals a pulmonary infiltrate in the lower lobe of the left lung. Results from sputum potassium hydroxide preparation are shown below. Which of the following is the most likely cause of this patient's condition?

Question

A 48-year-old man comes to the physician with a 6-month history of cough and fatigue.  He also has experienced malaise and weight loss.  He does not recall any sick contacts.  The patient is a carpenter.  He smokes 1 pack of cigarettes daily.  Temperature is 37.1 C (98.8 F).  Examination shows left lower lobe crackles.  HIV testing is negative.  Chest x-ray reveals a pulmonary infiltrate in the lower lobe of the left lung.  Results from sputum potassium hydroxide preparation are shown below.  Which of the following is the most likely cause of this patient's condition?

Quizplus · Accepted Answer

Blastomyces dermatitidis, a fungus endemic in the southeastern United States (states east of the Mississippi River), is present in soil and rotten organic matter. Blastomyces is a dimorphic fungus, meaning it assumes different forms at different temperatures. In the human body (37-40 C), it assumes the yeast form (single cells). The image shows a typical large yeast with a single, broad-based bud. The mold form (branching hyphae) predominates in the environment, at average temperatures of 25-30 C. Infection occurs by inhalation of aerosolized fungus from the environment. In about half of immunocompetent individuals, blastomycosis may present as a lung infection or cause a flu-like illness (fever, chills, myalgia, headache, nonproductive cough) or pneumonia (fever, cough, pleuritic chest pain). Pulmonary blastomycosis is diagnosed by finding the typical yeast forms. In immunocompromised patients, blastomycosis can cause disseminated disease. Patients experience systemic symptoms (fever, weight loss, night sweats), lung involvement (cough, dyspnea), skin lesions (papules, pustules, ulcers, verrucous lesions), and bone pain (caused by lytic lesions). (Choice A) Aspergillus fumigatus can cause lung disease in immunocompromised patients. It has only a mold form; in tissue samples it is seen as septate hyphae that branch at 45-degree angles. (Choice C) Candida albicans is characterized by small oval yeast with narrow-based budding. Candida pneumonia is a very rare disease. (Choice D) Coccidioides immitis is also a dimorphic fungus. It is seen as spherules (round encapsulated structures containing many endospores) in tissue samples. (Choice E) Cryptococcus neoformans causes lung disease and meningitis in immunocompromised patients. In contrast to blastomycosis, it forms round yeast with variable sizes and narrow-based buds. Cryptococcus has a thick polysaccharide capsule that appears clear with India ink staining and stains red with mucicarmine. (Choice F) Histoplasma capsulatum can cause lung disease. Like Blastomyces, it is a dimorphic fungus. Unlike Blastomyces, the yeast form of Histoplasma is smaller and is often found intracellularly within macrophages. H capsulatum is endemic in parts of the central and eastern United States along the Ohio and Mississippi river valleys. (Choice G) Rhizopus species can cause lung disease in immunocompromised patients. Rhizopus is the most common genus causing mucormycosis. It has only a mold form, with broad ribbon-like hyphae with rare septations. Educational objective: Blastomyces dermatitidis is a dimorphic fungus seen in tissue as round or oval yeasts with thick walls and broad-based budding. It is endemic in the southeastern United States (states east of the Mississippi River). The lungs are the primary site of involvement, and the skin and bone are the major sites of dissemination.

A 48-Year-Old Man Comes to the Physician with a 6-Month