eMedicine Specialties > Pulmonology > Infectious Lung Diseases

Blastomycosis

Author: Basil Varkey, MD, FCCP, Professor, Department of Internal Medicine, Division of Pulmonary and Critical Care, Medical College of Wisconsin; Consulting Pulmonologist, Froedtert Memorial Lutheran Hospital
Coauthor(s): Gregory J Raugi, MD, PhD, Professor, Department of Internal Medicine, Division of Dermatology, University of Washington at Seattle; Chief, Dermatology Section, Primary and Specialty Care Service, Veterans Administration Medical Center of Seattle
Contributor Information and Disclosures

Updated: May 21, 2008

Introduction

Background

In 1894, Gilchrist first described blastomycosis in the United States. Blastomycosis is a granulomatous fungal infection caused by Blastomyces dermatitidis. Serological studies that use enzyme-linked immunoassay indicate that different genotypes of B dermatitidis exist.

Blastomycosis is a common infection among dogs in endemic areas. It may serve as an indicator of human disease because of the shared environment. Blastomycosis is reported in other animals, including the horse, cow, cat, bat, and lion.

The following other eMedicine articles on blastomycosis may be helpful:

• Blastomycosis
• Blastomycosis, Thoracic
• South American Blastomycosis

Additionally, the Medscape CME course Fungal Disease: An Update may of interest.

Pathophysiology

Infection occurs by inhalation of aerosolized conidial forms of the fungus from its natural soil habitat. Once inhaled in the lungs, the conidia transform at body temperature to the yeast phase (thermal dimorphism). This transformation provides a survival advantage to the infecting fungus as the thick cell wall of the yeasts provides resistance to phagocytosis and induces expression of an immune-modulating virulence factor (BAD1) on the cell surface. Then, the yeast forms multiply and may disseminate through the blood and lymphatics to other organs. The evoked pyogranulomatous inflammatory response has an initial influx of neutrophils, followed by macrophage and granuloma formation.¹

Pulmonary infection may be asymptomatic in nearly 50% of patients. In others, the median incubation period, from inhalation of the fungus to manifestations of symptoms, is 45 days (range 21-106 d). Pulmonary symptoms of varying severity are common, and they most often occur without any symptoms of dissemination to other organs. Extrapulmonary dissemination more often occurs in patients with chronic pulmonary illness and in those who are immunocompromised.

The skin is the most common site of extrapulmonary blastomycosis and is involved in about 20-40% of the cases. Other areas affected, in order of frequency, are the bones (10-25%), prostate and other genitourinary organs (5-15%), and the meninges and brain (~5%). In rare instances, any organ can be affected, including the breast, eye, larynx, trachea, and ear. Reactivation of blastomycosis may occur after a pulmonary infection that resolved with, or without, treatment. An extrapulmonary site only rarely is a site of reactivation (eg, skin, bone, brain).

Frequency

United States

Most cases of blastomycosis occur in the United States. It is endemic in the central and southeastern parts of the country (eg, near the Mississippi River, Ohio River, Great Lakes). True incidence and prevalence are unknown, because there are no reliable antigen markers for skin testing. Based on confirmed cases, the annual incidence is less than 1 case per 100, 000 people in Mississippi, Kentucky, Arkansas, and Wisconsin. Within the endemic areas (eg, Vilas County, Wisconsin), infection by hyperendemic foci is reported at an annual incidence rate of 40 per 100,000.²

International

Blastomycosis is distributed throughout the world. Most reported cases outside of the United States are from Canada (Ontario, Manitoba) and the African continent . Cases have also been reported from disparate regions — Mexico, South America, Middle East, India

Mortality/Morbidity

Retrospective reports in the 1960s indicate a mortality rate of 42% in untreated blastomycosis and 5% in treated cases. Reports in the 1990s indicate a mortality rate of 0-2% in treated cases among immunocompetent patients. In contrast, the mortality rate in immunocompromised patients is 29%³ and in the subgroup of patients with AIDS is 40%.⁴ The reported mortality rate of patients presenting as adult respiratory distress syndrome (ARDS) is 68%.⁵ Complications generally do not occur in immunocompetent patients, and patients can expect a full recovery.

Race

No known racial predilection exists.

Sex

Blastomycosis was thought to occur more often in males than females; however, analysis of outbreak cases from a common source and recent reports do not indicate a significant sex difference. A recent report from Wisconsin revealed that 55 of the 120 cases of blastomycosis were in women (nearly 1:1 male-to-female ratio).

Age

The mean age at diagnosis is approximately 45 years. Most patients are aged 30-69 years; however, persons of any age can acquire the disease. Blastomycosis also occurs in infants and the very elderly.

Clinical

History

• Most symptoms conform to one of the following patterns of respiratory illness:
  • A flulike illness with fever, chills, myalgia, headache, and a nonproductive cough may occur, which resolves within days. Because of the brief and self-limited nature of these symptoms, blastomycosis may go undiagnosed except in the setting of a known outbreak.
  • The patient may present with an acute illness resembling bacterial pneumonia, with symptoms of high fever, chills, a productive cough, and pleuritic chest pain. Sputum is mucopurulent or purulent.
  • Chronic illness may occur and simulate tuberculosis or lung cancer, with symptoms of low-grade fever, a productive cough, night sweats, and weight loss. Sputum is mucopurulent or purulent, and hemoptysis may be present.
  • The patient may present with a fast, progressive, and severe disease that manifests as ARDS, with fever, shortness of breath, tachypnea, hypoxemia, and diffuse pulmonary infiltrates.
• Skin lesions, although usually asymptomatic, may be the presenting complaint.
• Bone lytic lesions cause bone or joint pain.
• Prostatitis may be asymptomatic or may cause pain on urinating.
• Laryngeal involvement causes hoarseness.

Physical

The physical examination may not reveal any abnormal findings. In the pneumonic form, findings may be present that are associated with pneumonic consolidation (eg, dullness on percussion, bronchial breath sounds, egophony, rales). Decreased or absent breath sounds suggest pleural effusion. Occasionally, erythema nodosum may be observed in association with pulmonary blastomycosis.

• Skin lesions are more common on the face, neck, and extremities. Early in the disease course, the lesions are sharply demarcated papules. Later, they expand to form ulcerated lesions with small pustules at the margins. Central healing and scar formation occur as the lesions grow larger. Some are verrucous, with raised irregular borders; multiple lesions may appear simultaneously or in sequence.
  • Lesions begin as papules or pustules or as subcutaneous nodules. Within a few weeks to months, the primary lesions evolve into ulcers, with indurated dusky or violaceous granulomatous or verrucous borders, or into vegetating plaques. Typically, the border is arciform or serpiginous, contains numerous tiny pustules or microabscesses covered with crust, and rises abruptly from the normal surrounding skin. Over a period of months to years, the lesions enlarge, eventually involving a substantial portion of the face, for example, and produce severe disfigurement. As the lesions enlarge, they heal centrally, with atrophic scar studded with telangiectasia.
  • Although the vast majority of patients with cutaneous blastomycosis acquire it by dissemination from a pulmonary focus, a few well-documented cases of primary cutaneous (inoculation) blastomycosis have been described in laboratory workers. The skin lesions are described as "chancriform" and are accompanied by nodular lymphangitis.
• Bone involvement rarely leads to a draining abscess. The involved joint may be tender and swollen.

• Search for CME/CE on This Topic »

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