Histoplasmosis - Diagnosis

What were the tests you had that led to a diagnosis of histoplasmosis? Where were you living at the time?

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How is histoplasmosis diagnosed?

Definitive diagnosis of histoplasmosis can be complicated, especially if the patient gives no history of exposure to areas contaminated with H. capsulatum. Many bacterial and fungal infections can produce clinical findings that are found with H. capsulatum infections (for example, granulomatous nodules found in sarcoidosis and tuberculosis, or lung infiltrates seen on X-ray in coccidiodomycosis, blastomycosis, aspergillosis, and other lung infections). In fact, before 1932, many patients with chronic pulmonary histoplasmosis were diagnosed as having tuberculosis. Differentiating histoplasmosis from other lung infections can still be a diagnostic challenge for clinicians.

Cultures of blood, sputum, or tissue biopsy samples can be cultured on media that supports H. capsulatum growth. If H. capsulatum is cultured, the diagnosis is confirmed. However, at best, cultures are positive in only about 60% of patients with chronic pulmonary infections and are positive in only about 15% of acute cases. Furthermore, it may take from two to 12 weeks for the fungus to grow enough to be identified in culture, which could delay treatment especially in progressive disseminated cases. Blood cultures range from 50%-90% positive in progressive disseminated cases. Positive cultures for H. capsulatum definitively diagnose histoplasmosis. Unfortunately, acute progressive disseminated histoplasmosis, if not treated quickly and appropriately, can lead to death in a few weeks. In suspected cases, treatment should begin immediately without waiting on cultures to grow positive for H. capsulatum.

There are several types of serology tests (tests for antigens and antibodies) that are used on blood, urine, and cerebral spinal fluid (CSF). They can give fairly rapid results especially with symptomatic, chronic, or progressive disseminated disease (75%-95% positive after six weeks) but take about three weeks to be positive in a small number (about 15%) of acute cases. Unfortunately, the reagents share some cross-reactivity with other fungal genera (for example, Aspergillus, Blastomyces, and Coccidioides), so false-positive results can be obtained. Further, these tests for H. capsulatum can be positive in people that live in areas with endemic histoplasmosis and also can be positive in patients that have inactive disease.

Stains (Giemsa stain or methenamine silver stain) of tissue samples, blood, sputum, bone marrow, lymph node aspirates, and other fluids can allow microscopic visualization of H. capsulatum. However, the accuracy of identification depends on the experience of the observer as other organisms may resemble H. capsulatum. Researchers suggest this method be backed up by other tests such as serology and cultures.

Many other tests may be used to help the physician determine the extent of infection by H. capsulatum. Examples are listed below:

  • CBC or complete blood count: Low white blood cell counts can occur in chronic progressive histoplasmosis.
  • Chest X-rays can show lung changes (infiltrates, cavitations, and enlarged lymph nodes) that may occur in chronic and acute progressive disseminated histoplasmosis.
  • CT scan may show bilateral adrenal gland involvement in subacute progressive disseminated histoplasmosis.
  • Echocardiography helps determine if heart valves are infected or if pericarditis is present in acute pulmonary or progressive disseminated histoplasmosis.
  • Alkaline phosphatase levels in the blood are increased in chronic pulmonary and acute progressive disseminated histoplasmosis.

Other tests and procedures may be done to help determine the diagnosis or extent of infection; those listed above are the most common. Occasionally, a surgeon may need to be consulted to obtain lung tissue, pleural fluid, or lymph node biopsy for culture and microscopic evaluation to aid diagnosis.

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See what others are saying

Comment from: teresa, 45-54 Female (Patient) Published: April 17

I was diagnosed with histoplasmosis when I was 16 years of age, due to a chronic cough and fatigue. I was sent to a specialist, admitted to the hospital and had some tests. The first thing done was a skin test, with positive results. The next thing done was a light run into my lungs, a bronchoscopy. I am now 54 years old and have been having problems breathing for the past few months. My doctor has given me Sporanox to take, after sending me to have lab tests to check for any fungus. The lab tests came back positive for histoplasmosis. I also have been diagnosed with ocular histoplasmosis.

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