Chronic cavitary histoplasmosis
Chronic pulmonary histoplasmosis is a chronic respiratory infection caused by inhaling the spores of the fungus, Histoplasma capsulatum. This fungus is commonly found in the soil in states along the Mississippi or Ohio river valleys of the US.
Causes, incidence, and risk factors
Histoplasmosis is caused by a fungus found in the soil of the central and eastern United States (especially Mississippi and Ohio river valleys), eastern Canada, Mexico, Central America, and South America. The primary infection (acute histoplasmosis) usually causes no symptoms, or only mild disease that is easily overcome by an normal immune system.
Chronic pulmonary histoplasmosis occurs in individuals with structurally abnormal lungs, such as smokers with emphysema or COPD (chronic obstructive pulmonary disease). In these individuals, the acute infection with histoplasmosis lingers and progresses, causing symptoms and chest x-ray findings that mimic pulmonary tuberculosis.
Although many of these infections in these abnormal lung spaces eventually heal, some infections persist, causing enlargement of lung spaces and destruction of nearby normal lung tissue. Scarring and cavities may occur as a result of this chronic infection.
Risk factors include:
- Travel or residence in central or eastern United States
- Exposure to soil or particles contaminated with droppings of chickens, bats, or blackbirds
- Preexisting COPD
- Compromised immunity such as in people who have AIDS
- Unintentional weight loss
- Cough that brings up mucus or pus
- Shortness of breath
- Joint stiffness
- Skin involvement (erythema nodosum)
Signs and tests
Tests that may be used in the diagnosis of chronic pulmonary histoplasmosis include:
- Chest x-ray
- Chest CT scan
- Sputum culture and stain
- Biopsy of infected tissue, such as open lung biopsy, or bone marrow biopsy
- Bronchoscopy with transbronchial biopsy or bronchoalveolar lavage
- Histoplasma complement fixation titer
- Histoplasma urinary antigen test
- Immunodiffusion test for precipitating antibodies to antigens of histoplasma
Antifungal medications are prescribed to control the infection within the lung. Itraconazole (by mouth) or amphotericin B (intravenously) is usually successful.
The infection usually responds to antifungal medication, but the fibrotic (scarring) changes within the lung often remain. Prognosis for chronic pulmonary histoplasmosis is favorable, but many patients continue to be ill due to their pre-existing emphysematous lung disease.
Rarely, pulmonary histoplasmosis can progress to disseminated histoplasmosis, which is the spread of infection through the blood to other organs. People who have suppressed immune systems and very young children are more likely to develop disseminated histoplasmosis. If this progression occurs, the prognosis is less favorable .
- Disseminated histoplasmosis
- Respiratory insufficiency
- Lung scarring (fibrosis)
Calling your health care provider
Call for an appointment with your health care provider if symptoms of chronic pulmonary histoplasmosis develop.
Call your health care provider if symptoms continue despite treatment, or if breathing difficulty or symptoms of disseminated histoplasmosis occur.
Avoiding travel to areas where this spore is found would prevent exposure, but this may not be practical. Avoid bird or bat droppings if you are in one of these areas, especially if you are immunosuppressed.
by Gevorg A. Poghosian, Ph.D.