Cryptococcosis

Posted by Graham McMahon • September 16th, 2011

In this week’s Case Record of the Massachusetts General Hospital, a 74-year-old man with pemphigus vulgaris was referred for evaluation of lung nodules. Imaging of the chest revealed multiple ill-defined nodules, some with marked 18F fluorodeoxyglucose avidity. A diagnostic procedure was performed.

Cryptococcosis is most often seen in the United States in patients with advanced HIV infection, but a number of other conditions can predispose to cryptococcal infection, including idiopathic CD4 lymphocytopenia, transplantation, connective-tissue disease, malignant tumors, glucocorticoid therapy, chronic obstructive pulmonary disease, cirrhosis, and sarcoidosis.

Clinical Pearls

How is cryptococcal infection contracted?

Cryptococcal infection begins with inhalation of the basidiospores of the fungus. Cryptococcal cells are yeasts with a small capsule. The survival of cryptococcal cells in the environment and inside the mammalian and nonmammalian hosts depends on the presence of the capsule and the production of the antioxidant melanin. Most patients who have clinically symptomatic cryptococcal infection have been exposed to cryptococcus sometime in the past, and developed a primary infection that was asymptomatic. The infection persists in a latent state until the patient’s immune system is suppressed.

What are the forms of pulmonary cryptococcosis?

Cryptococcus can produce several forms of disease in the lung, depending in part on the degree of the patient’s immunosuppression. In patients with a low degree of immunosuppression, the infection results in fibrocaseous cryptococcoma with central necrosis surrounded by a fibrous capsule, or as in this patient, it results in less well circumscribed, granulomatous pneumonia. Histiocytic pneumonia or mucoid pneumonia with few inflammatory cells may be seen in patients who have a high degree of immunosuppression. In a profoundly immunosuppressed host, yeast forms may plug the capillaries as a manifestation of cryptococcal sepsis, with essentially no cellular reaction in alveoli.

Table 1. Select Differential Diagnosis of Lung Nodules in This Patient.

Morning Report Questions

Q: How should the diagnosis of cryptococcosis be established in patients with pulmonary nodules?

A: In order to establish the diagnosis of cryptococcosis, a lung biopsy should be performed. A serum cryptococcal-antigen assay is not adequate to make the diagnosis in this case, since among HIV-negative patients, it is positive in only 56% of patients with pulmonary disease.

Q: How is disseminated cryptococcosis treated?

A: Disseminated cryptococcosis is treated with intravenous liposomal amphotericin and oral flucytosine, followed by oral fluconazole

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