12 Dermatopathology Case Reviews: The Histology of Fungal & Parasitic Infections

This video provides a comprehensive overview of the histological diagnosis of deep fungal infections, highlighting key features to differentiate between various organisms and conditions. It reviews where to look for organisms in tissue and presents cases of Coccidioidomycosis, Cryptococcus, Blastomycosis, and Sporotrichosis. Dr. Davis also explains how to distinguish between Histoplasmosis and Leishmaniasis and between different types of mycetomas and infections caused by dematiaceous fungi.

A key to diagnosis is understanding the morphology and size of common deep fungal organisms. The video highlights the importance of recognizing the common histologic patterns associated with infections, such as pseudoepitheliomatous hyperplasia with pus or the presence of parasitized histiocytes.

High-Yield Areas for Organism Detection: To improve the chances of finding the organism, the presenter advises pathologists to look in specific areas of the tissue. These include neutrophilic microabscesses, zones of necrosis, and within the cytoplasm of multinucleated giant cells.

To view the slides for this presentation, please follow this link:

https://sagis.pathpresenter.net/public/presentation/display?token=bc89d450

Case Studies:

• Coccidioidomycosis vs. Rhinosporidiosis: Coccidioidomycosis is identified by its large spherules (30-50 microns) with a thick, refractile wall. This is contrasted with Rhinosporidiosis, which has much larger spherules (100-400 microns).

• Cryptococcus: This fungus is characterized by its pleomorphic yeast forms and a prominent gelatinous capsule. The capsule stains with musicarmine, while the organism itself stains with PAS, GMS, and Fontana-Masson.

• Blastomycosis: A diagnosis of Blastomycosis is often made when thick-walled, asymmetrically budding yeast forms are found. In immunosuppressed patients, the condition presents with pseudoepitheliomatous hyperplasia with pus.

• Lobomycosis: This infection is almost exclusive to Central and South America. It’s characterized by fungal cells arranged in a “pop-bead” like chain.

• Sporotrichosis: This is a challenging diagnosis because the organisms are typically few and far between, making it difficult to find them on histology, even with special stains.

• Histoplasmosis vs. Leishmaniasis: Both of these conditions cause parasitized histiocytes, but the location of the organisms is different. In Histoplasmosis, the organisms “stuff” the cytoplasm, while in Leishmaniasis, they tend to cluster at the periphery of the histiocyte, creating a “ferris wheel” or “marquee” sign.

• Mycetomas: The video distinguishes between eumycetoma (a true fungus) and actinomycetoma (a filamentous bacteria) by identifying the type of organism within the “grains” found in the tissue.

• Protothecosis: This infection is caused by achloric algae. The characteristic feature is the “morula” or “mulberry-like” cells, which are sporangia with internal septation.

• Dematiaceous Fungi: This group is distinguished by the morphology of the organisms. Phaeohyphomycosis is diagnosed when pigmented hyphal elements are seen, while Chromoblastomycosis is characterized by the presence of pigmented spores, sometimes called “medlar bodies” or “copper pennies.”