Thoracic (or pulmonary) histoplasmosis refers to pulmonary manifestations from infection with the organism Histoplasma capsulatum which is an organism endemic to El Salvador but can be found widely in other parts of North, Central and South America. It can have variable clinical and radiographic presentation 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 significant populations of bats and birds.
acute pulmonary histoplasmosis
- 90% of cases can have no symptoms
- symptoms manifest at up to two weeks after exposure
- fever, malaise, headache, myalgia, abdominal pain
- dyspnoea can manifest if there is diffuse involvement
- cough and haemoptysis can be a prominent feature if there is a degree of airway compression
- rarely dysphagia occurs with oesophageal compression
chronic pulmonary histoplasmosis
- usually, develops in those with underlying pathologies such as emphysema or COPD 5
- continuing symptoms for more than three months
disseminated progressive histoplasmosis
- more likely in patients with deficient cell-mediated immunity including those with AIDS (CD4 < 150 cell/uL), 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 travelled in endemic regions.
The particular imaging features are related to the timeline of presentation and the patient's ability to mount an immune response.
- Well-defined nodules which have central calcification
- 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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