Mediastinal granuloma due to histoplasmosis in a patient on infliximab

GOLD STANDARD FOR DIAGNOSIS

Isolation of H capsulatum from clinical specimens remains the gold standard for confirmation of histoplasmosis. The sensitivity of culture to detect H capsulatum depends on the clinical manifestations: it is 74% in patients with disseminated histoplasmosis, but only 42% in patients with acute pulmonary histoplasmosis.¹¹ The serum histoplasma antigen test has a sensitivity of 91.8% in disseminated histoplasmosis, 87.5% in chronic pulmonary histoplasmosis, and 83% in acute pulmonary histoplasmosis.¹²

Urine testing for histoplasma antigen has generally proven to be slightly more sensitive than serum testing in all manifestations of histoplasmosis.¹³ Combining urine and serum testing increases the likelihood of antigen detection.

TREATMENT

Asymptomatic patients with mediastinal histoplasmosis do not require treatment. (Note: in some cases, lymphadenopathy is found incidentally, and biopsy is done to rule out malignancy.)

Standard treatment of symptomatic mediastinal histoplasmosis is oral itraconazole 200 mg, 3 times daily for 3 days, followed by 200 mg orally once or twice daily for 6 to 12 weeks.¹⁴

Although stopping immunosuppressant drugs is considered the standard of care in treating histoplasmosis in immunocompromised patients, there are no guidelines on when to resume them. However, a retrospective study of 98 cases of histoplasmosis in patients on tumor necrosis factor antagonists found that resuming immunosuppressants might be safe with close monitoring during the course of antifungal therapy.⁹ The role of long-term suppressive therapy with antifungal agents in patients on chronic immunosuppressive therapy is still unknown and needs further study.

TAKE-HOME MESSAGES

• Histoplasmosis is the most prevalent endemic mycotic disease in the United States, and mediastinal lymphadenopathy is commonly seen in acute pulmonary histoplasmosis.
• Histoplasmosis should be included in the differential diagnosis of granulomatous lung disease in patients from an endemic area or with a history of travel to an endemic area.
• Immunosuppressive agents such as tumor necrosis factor antagonists and disease-modifying antirheumatic drugs can predispose to invasive fungal infection, including histoplasmosis.
• While isolation of H capsulatum from culture remains the gold standard for the diagnosis of histoplasmosis, the histoplasma antigen tests (serum and urine) is more sensitive than culture.