A 35-year-old man, a highly stressed business executive from Birmingham, complains about a nasty lesion on his leg that won't go away. The man works about 90 hours per week and hates to take time off for things like visits to a physician, so he has tried (for several weeks) to treat the lesion himself with an OTC topical ointment that contains bacitracin. Unfortunately, this didn't help; the lesion just continued to enlarge and look more serious. Now, it has finally gotten ugly enough to scare the executive into taking a little time off to seek professional advice.

On examination, the rather impressive lesion is found to be about 4 cm in diameter. It is on the left leg, near the knee, and is ulcerated, with a surrounding area of fibrosis, edema, and erythema. Despite the ugly appearance of the lesion, it is not overly painful. The man says that, when he first noticed it about 2 months ago, it was only about 5 mm in diameter and looked a little like a common boil.

The physician asks the man if he participated in any extended outdoor activities during the past six months. The man says that, about four months ago, he took a rare weekend off in order to hike in a wilderness area with a group of his co-workers. The group hiked along a relatively unspoiled tributary of the Mississippi River in Louisiana for two days and then enjoyed a fine dinner in New Orleans. The man feels that, except for the sore on his leg, he has been in good health. However, he admits that he doesn't take vitamins, watch what he eats, exercise, or make any other significant effort to take care of himself. His job really is extremely stressful. He doesn't smoke, but he sometimes drinks pretty heavily after he gets home in the evening.

Question 7.1: What is your diagnosis?

The appearance and nature of the lesion is suggestive of blastomycosis, also known as Gilchrist's disease, Chicago disease, and North American blastomycosis. The man history of a hike in the wilderness near a river several months previously is consistent with this diagnosis. The differential includes bromoderma, pyoderma gangrenosum, giant keratoacanthoma, and squamous cell carcinoma. Mycobacterium marinum infection is another possibility, depending on whether that bacterium is sensitive to bacitracin.

Question 7.2: What is the causative agent?

Blastomycosis is caused by Blastomyces dermatitidis, a pathogenic fungus. This organism grows at room temperature as a white or tan mold (i.e., a multicellular, filamentous fungus). Inside of a human host or at 37(C, however, it assumes a unicellular, budding yeast form.

Question 7.3: How is the diagnosis confirmed?

Presumptive diagnosis can be made by visualizing the distinct yeast forms in KOH preparations of clinical specimens. (An expert can recognize the yeast form of B. dermatitidis with ease.) For this case, the clinical specimen would be a scraping of the lesion or a sample of pus, if the lesion is exuding pus. To confirm the diagnosis, it is necessary to culture the causative fungus from an appropriate specimen on Sabouraud's agar or some other enriched medium designed specifically for pathogenic fungi.

Test Results:

Microscopic examination of a KOH-treated scraping of the patient's lesion revealed the presence of numerous yeast-like forms typical of those produced by B. dermatitidis. The lab reports that it cultured a pathogenic fungus from the lesion scraping and that an expert identified their isolate as B. dermatitidis.

Question 7.4: How did the patient become infected?

Infection occurs by inhalation of the fungus from the environment. This disease is generally not transmitted person-to-person. Therefore, the man probably inhaled the fungus while he was hiking with his co-workers in Louisiana. One of the more likely places to find B. dermatitidis in the environment is along a river or other body of water, where it grows profusely in rotting wood or other decomposed vegetation when the moisture levels are fairly high.

Question 7.5: Where is this disease endemic?

Blastomycosis is uncommon in any locality, but most cases occur in the southeastern, south-central, and mid-Atlantic regions of the U.S. Occasional cases are seen in other regions of the U.S. and Canada. Cases have also been reported in Africa, Mexico, and Central and South America.

Question 7.6: How does the disease progress?

The lungs are the initial site of infection, but pulmonary symptoms may or may not occur prior to the development of other problems like this patient's lesion. Many cases are asymptomatic, but others produce an acute, self-limited pneumonia, with fever, productive cough, malaise, and myalgias. In most patients, the disease has an indolent onset and a chronically progressive course. Chronic infection may result in fever, chronic cough, weight loss, lassitude, chest aches, and/or skin lesions. Symptoms vary wide from one patient to another, but the skin lesions are most frequently seen extrapulmonary symptom. The fungus reaches the skin via hematogenous dissemination from the lungs. Lesions might not appear until 1-3 months after the initial infection, after which they enlarge over many weeks.

Question 7.7: What could happen if this patient were immunocompromised?

In immunocompromised patients, blastomycosis can lead to widely disseminated infections that involve the skin, bones and joints, genitourinary tract, central nervous system, and other parts of the body. If not treated successfully, these infections have a high mortality rate.

Question 7.8: How should you treat this case?

Various antifungal drugs can be used to treat chronic cases such as this one, including amphotericin B, itraconazole, ketoconazole, and fluconazole. Surgery might be indicated with antifungal therapy for drainage of large abscesses. The prognosis is reasonably good with proper treatment (mortality rate up to 60% prior to availability of antifungal drugs). The relapse rate for patients treated with amphotericin B is about 5% (much higher in AIDS victims).