Using immunohistochemistry to assess the accuracy of histomorphologic diagnosis of aspergillosis and mucormycosis

Background: Data on the accuracy of conventional histomorphologic diagnosis are limited, especially in mucormycosis. We therefore investigated the accuracy of histomorphologic diagnosis of mucormycosis and aspergillosis, using immunohistochemistry (IHC) tests for mucormycosis and aspergillosis.

Methods: Patients enrolled met the modified criteria for proven and probable mucormycosis (during a 22-year period) or invasive aspergillosis (during a 6-year period) and had formalin-fixed, paraffin-embedded tissues available. We first tested the diagnostic performance of IHC for mucormycosis and aspergillosis in proven cases. Then we determined the accuracy of histomorphologic diagnosis of probable cases, using the IHC tests.

Results: In 7 proven cases of mucormycosis, the sensitivity and specificity of mucormycosis IHC were 100% (95% confidence interval, 65%-100%) and 100% (68%-100%), respectively. In 8 proven cases of aspergillosis, and the sensitivity and specificity of aspergillosis IHC staining were 87% (53%-98%) and 100% (65%-100%), respectively. Of 23 probable mucormycosis cases, 20 (87%) were positive with mucormycosis IHC, 2 (9%) were positive with aspergillosis IHC (including 1 positive for both), and 2 were negative with both. Of 16 probable aspergillosis cases, 10 (63%) were positive with aspergillosis IHC, 4 (25%) were positive with mucormycosis IHC, and 2 (13%) were negative with both tests.

Conclusions: Aspergillosis and mucormycosis seem not to be correctly diagnosed morphologically, because some of the probable cases showed either test with both antibodies or failure to stain with the homologous antibody. In the absence of fungal culture results, the IHC tests seem helpful in differentiating between aspergillosis and mucormycosis.