Thoracic (or pulmonary) histoplasmosis refers to pulmonary manifestations from infection with the fungus Histoplasma capsulatum which is an organism endemic to the Central American state of El Salvador but can be found widely in other parts of both North and South America. It can have variable clinical and radiographic presentations depending on the state of infection and other host co-morbidities.
It is considered the most common systemic fungal infection in North America 3. Most of these are thought to be sporadic in nature, although outbreaks have been reported.
Some populations studies have shown that over 80% of young adults from endemic regions of North America have been previously infected by Histoplasma capsulatum 4.
Features interrogated in the history should include travel to endemic areas as well as exposures to significant populations of bats and birds.
acute pulmonary histoplasmosis
- 90% of cases can have no symptoms
- symptoms manifest for up to two weeks after exposure
- fever, malaise, headache, myalgia, polyarthralgia and abdominal pain
- dyspnea can manifest if there is diffuse involvement
- cough and hemoptysis can be a prominent feature if there is a degree of airway compression
- rarely dysphagia occurs with esophageal compression
- subacute pulmonary histoplasmosis
- chronic pulmonary histoplasmosis
disseminated progressive histoplasmosis
- more likely in patients with deficient cell-mediated immunity including those with AIDS (CD4 <150 cell/μL) or on corticosteroids
- can often be fatal
Most patients with thoracic histoplasmosis are thought to have normal chest radiographs. Where there are findings, these can be non-specific to a range of infectious or inflammatory disorders and histoplasmosis is considered in the differential if the patient is known to have traveled in endemic regions.
The particular imaging features are related to the timeline of the presentation and the patient's ability to mount an immune response.
- well-defined nodules which have a central calcification giving them a "target lesion" which is pathognomonic
- airspace shadowing with consolidation involving multiple lung segments or lobes similar to bacterial pneumonia
- pleural effusions are possible but uncommon
- healing process with formation of histoplasmomas, which are well-defined nodules with central calcifications
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