This video presents a dermatopathology case study of a skin biopsy diagnosed as Coccidioidomycosis. The analysis begins by identifying a key histological pattern: pseudoepitheliomatous hyperplasia (PEH) combined with underlying granulomatous and suppurative (pus-forming) inflammation. This pattern is highlighted as a strong indicator for an underlying deep fungal or mycobacterial infection. The video details the microscopic identification of the causative organism, Coccidioides, which appears as large, round spherules with a characteristic double-layered, refractile wall, sometimes containing endospores. The presenter emphasizes the diagnostic approach, which includes searching for organisms on H&E stain, utilizing special stains (GMS, PAS, Fite), and stresses the critical importance of recommending tissue cultures to the clinician, as cultures can be more sensitive than histology, especially when the pattern is suggestive but organisms are not visualized. The case concludes with a brief overview of the epidemiology of Coccidioidomycosis as an infection endemic to the American Southwest.
Diagnosing Coccidioidomycosis in a Skin Biopsy
0:00:07 Initial Findings: The biopsy shows pseudoepitheliomatous hyperplasia (PEH), a reactive and dramatic thickening of the epidermis, with significant inflammation, giant cells, and lymphocytes in the dermis below.
0:01:06 Key Diagnostic Pattern: The combination of PEH with either neutrophils (pus) or granulomas is a classic pattern that should immediately raise suspicion for a deep infection. While this case has more granulomas than neutrophils, it fits the pattern.
0:01:23 The Diagnosis is Coccidioidomycosis: The speaker identifies the infection as Coccidioidomycosis. This pattern is also common in other deep fungal infections like Blastomycosis and Chromoblastomycosis, but notably not in Cryptococcus.
0:02:35 Supporting Clues for Infection: Seeing granulomas mixed with neutrophils or a high number of plasma cells are additional "soft clues" that point towards an infectious cause.
0:03:08 Identifying the Organism: The Coccidioides fungus is identified on the standard H&E slide without needing special stains. It appears as large, round spherules (cysts) that often look empty. Key features for identification are the thick, double-layered, refractile wall and the potential presence of tiny internal endospores, which can look like grainy, purplish material.
0:04:09 Finding the Organisms: The fungal organisms can be sparse and require careful searching. They are often located within the granulomas, inside giant cells, or can even be pushed up into the hyperplastic epidermis.
0:04:41 Importance of Clinical Correlation & Cultures: A critical takeaway is that if a pattern is highly suspicious for infection but no organisms are found on H&E or special stains, it is essential to communicate this suspicion to the dermatologist. Recommending a repeat biopsy for tissue cultures is crucial, as cultures can sometimes identify an organism when histology cannot.
0:05:23 Epidemiology of Coccidioides: This is a soil-dwelling fungus endemic to the American Southwest, such as Arizona and California's San Joaquin Valley, which can cause lung and skin infections.