Mycotic Infections of the Lung

Key Points

• Several organisms can cause mycotic lung infections, with varied clinical presentations ranging from the asymptomatic patient with a subclinical infection to the immunocompromised patient with a life-threatening invasive opportunistic fungal infection.
• A heightened index of suspicion is essential when confronted with patients with pulmonary symptoms, especially those with refractory or atypical infections. Patients who are malnourished, debilitated, diabetic, or receiving intensive or long courses of antibiotic therapy are at increased risk of mycotic infections. Patients with blood dyscrasias, lymphatic malignancies such as Hodgkin’s disease or immunosupressed also are at increased risk.
• Respiratory tract symptoms such as fever, cough, sputum production, hemoptysis, or pleuritic pain usually provide the indication for a conventional chest radiograph and computed tomography. Imaging is necessary for delineating pulmonary mediastinal or pleural involvement.
• A confirmed diagnosis of fungal infection can be made only after the demonstration of the presence of the organism in body exudates or tissues. Stronger proof is provided by growth in culture; however, the mere recognition of the organisms in smears, fresh mounts, or tissue sections has usually been sufficient for diagnosis.
• Occasionally, fungi can spread to the lungs hematogenously from another source, but the presence of fungi in the lung results most frequently from inhalation of fungal organisms. In the vast majority of patients, asymptomatic or mild pulmonary infection clears spontaneously without significant debility. In cases of systemic fungal infection, the portal of entry again, with rare exception, is the airway.
• HEADING Historical Note

Some of the first advances and developments in the understanding of fungal infections of the lung occurred in the early 1950s during the emergence of resectional surgery for the therapy of tuberculosis. With the advent of pulmonary resection as a therapy for tuberculosis, it became apparent that some of the patients thought to be afflicted with tuberculosis on the basis of their chest radiographic findings were, in fact, suffering from invasive and pathogenic fungal infections.[1] The first major non-surgical therapy for pulmonary fungal infections came with the isolation of amphotericin B from a soil actinomycete.[2]

Serious pulmonary fungal infection represents a relatively small proportion of pulmonary fungal infections in general. The vast majority of patients present with minimal symptoms that rapidly subside and have no sequela. An even larger number of patients develop primary fungal infections of a subclinical nature that is evidenced only by conversion of skin tests or serology.

With the increased use of immunosuppression for a growing number of autoimmune conditions, immunosuppression for organ transplantation, the widespread use of chemotherapy, and the spread of human immunodeficiency virus (HIV), there is an ever-increasing experience with fungal infections due to secondary or opportunistic pathogens in immunocompromised patients. Of all transplant patients, those with lung or heart-lung transplants are particularly vulnerable for fungal infection due to multiple reasons including: high level of immune suppression required, decreased mucociliary clearance and impaired lymphatics due to the transplant, and continuous environmental exposure of the allograft to pathogens. Additionally, immunocompromised patients may present with pulmonary infections due to a combination of fungal, bacterial and viral pathogens. Although they form a small minority of patients, it is in immunocompromised patients that we see the most serious manifestations of mycotic infections of the lung.