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Abstract:
This video discusses a dermatopathology case involving a punch biopsy from a middle-aged woman's thigh, presenting as an erythematous plaque with pustules, initially suspected clinically to be herpes zoster (shingles). Microscopic examination revealed significant inflammation around hair follicles and sebaceous glands, spongiosis, and neutrophils within the follicles, suggesting folliculitis. While herpes was considered, the key finding, initially subtle on H&E stain but confirmed with a GMS fungal stain, was the presence of numerous dermatophyte fungal hyphae within the stratum corneum and extending deep into hair follicles. This confirmed a diagnosis of tinea (dermatophytosis) with fungal folliculitis, also known as Majocchi's granuloma. The speaker emphasizes the importance of considering fungal infections, the diagnostic challenge posed by tinea incognito (fungal infection altered by steroid use), the limitations of H&E staining for detecting fungus, the necessity of special stains (GMS/PAS), and the critical treatment implication that follicular involvement often requires systemic oral antifungal therapy rather than just topical treatment.
Summary: Fungal Folliculitis (Majocchi's Granuloma) Case Study
0:00 Case Presentation: A punch biopsy was taken from an erythematous (red) plaque with pustules on the thigh of a middle-aged woman.
0:23 Initial Microscopic View: Shows inflammation around hair follicles/sebaceous glands, spongiosis (intercellular edema in the epidermis), and edema.
0:37 Clinical History & Initial Diagnosis: Patient visited urgent care, suspected of having shingles (Varicella Zoster), and received antiviral medication without improvement. No definite history of topical steroid use, but suspected.
1:07 Differential Diagnosis Considerations: Herpes Zoster was initially considered due to follicular inflammation, but no viral cytopathic effect was seen on H&E. Bacterial folliculitis was also considered due to neutrophils within follicles (2:12).
3:34 Key Microscopic Finding (H&E): Subtle fungal hyphae were identified within the stratum corneum (outermost skin layer) on the standard H&E stain.
4:08 Diagnosis: Dermatophytosis (tinea, or "ringworm"), a superficial fungal infection.
4:41 Follicular Involvement: The fungus extends down into the hair follicles, causing fungal folliculitis.
5:02 Majocchi's Granuloma: The specific term for dermatophyte infection involving hair follicles, often presenting clinically as perifollicular papules, pustules, or nodules. Follicle rupture can occur.
5:42 Treatment Implications: Fungal infections confined to the skin surface can often be treated with topical antifungals. However, when hair follicles are involved (Majocchi's), oral antifungal medication is usually necessary (6:02) because topical creams may not penetrate deeply enough.
6:33 Fungal Stain Confirmation (GMS): A Gomori Methenamine Silver (GMS) stain clearly highlights numerous fungal hyphae (staining black) within the stratum corneum and deep within the hair follicle, wrapped around the hair shaft (7:14), confirming the diagnosis and extent. PAS stain is an alternative.
8:38 Risk of Steroid Use: Treating fungal infections with topical steroids suppresses the immune response, potentially worsening the infection, driving it deeper into follicles, and altering its appearance (10:30).
11:11 Tinea Incognito: When steroid treatment alters the classic clinical appearance of ringworm, making it look unusual (e.g., a solid plaque instead of a ring), it's termed "tinea incognito," making clinical diagnosis difficult.
11:51 Clinical Pearl: If a suspected inflammatory rash (dermatosis) does not improve or worsens with topical steroid treatment, fungal infection should be strongly considered, prompting referral, biopsy, or skin scraping (KOH prep).
14:58 Difficulty Seeing Fungus on H&E: Dermatophyte fungi can be extremely subtle or invisible on standard H&E stains, even when abundant (15:56). Special stains (GMS or PAS) are often required for detection. Careful examination of special stains is needed as sometimes only rare organisms are present (16:59).