What are the histopathological features of tinea corporis?

Histopathological Features of Tinea Corporis

The histopathological diagnosis of tinea corporis relies on identifying fungal hyphae in the stratum corneum using special stains (PAS or GMS), along with characteristic inflammatory changes including neutrophils in the stratum corneum, compact orthokeratosis, and spongiosis with variable dermal inflammation. 1

Key Microscopic Features

Fungal Elements

• Hyphae are typically located in the stratum corneum and appear as septate, branching structures best visualized with Periodic Acid-Schiff (PAS) or Grocott-Gomori's methenamine-silver (GMS) stains 1
• The classic "sandwich sign" (fungal hyphae between two zones of cornified cells) may be present but is seen in only approximately 32% of cases, particularly in bullous variants 2
• Hematoxylin-eosin staining alone frequently fails to reveal fungal organisms, requiring special stains in up to 40% of cases to establish the correct diagnosis 2

Epidermal Changes

• Compact orthokeratosis (tight, basket-weave stratum corneum) is a characteristic finding 3
• Neutrophils within the stratum corneum and/or epidermis serve as an important diagnostic clue 3
• Spongiosis (intercellular edema) with variable intraepidermal vesiculation may be present 4
• Epidermal hyperplasia with acanthosis is common, reflecting increased keratinocyte proliferation 5

Dermal Features

• Prominent papillary dermal edema can be a striking finding, particularly in lesions on the extremities, and should prompt consideration of dermatophytosis even when other features are subtle 3
• Perivascular lymphocytic infiltrate in the superficial dermis is typical 3
• Dermal neutrophils as a non-predominant cell type are present in approximately 85% of cases and serve as an additional diagnostic clue 2
• Deep dermal inflammation may occasionally be present (25% of cases) and does not exclude the diagnosis 2

Variant Presentations

Bullous Tinea Corporis

• Subepidermal or intraepidermal blister formation with prominent neutrophilic infiltration 2
• Fungal hyphae are most commonly found in the stratum corneum adjacent to the blister rather than within the blister cavity itself 2
• May show frank bullae secondary to severe inflammation 4

Inflammatory Variants

• Vesicles and pustules with increased numbers of neutrophils 4
• Marked spongiosis that can mimic other inflammatory dermatoses including atopic or seborrheic dermatitis 4

Critical Diagnostic Considerations

Staining Requirements

• Routine PAS staining should be performed on all biopsies of inflammatory dermatoses where dermatophytosis is in the differential, as H&E alone is insufficient in many cases 3, 2
• Special stains are essential when clinical suspicion exists but organisms are not evident on routine sections 2

Common Pitfalls

• Misdiagnosis occurs when relying solely on H&E staining without special fungal stains, particularly in cases with prominent inflammation or bullous changes 2
• The absence of the classic sandwich sign does not exclude tinea corporis, as this feature is present in less than one-third of cases 2
• Prominent papillary dermal edema may lead to misdiagnosis as other conditions (such as arthropod bite reaction or urticaria) if fungal stains are not performed 3
• Deep inflammation should not dissuade from the diagnosis of this superficial infection 2

Correlation with Mycological Testing

• Histopathological diagnosis should be confirmed with fungal culture on Sabouraud agar, as species identification guides treatment selection and cannot be determined by histology alone 1
• When biopsies show prominent papillary dermal edema with negative PAS stains and patients fail conventional anti-inflammatory therapy, fungal culture should be pursued 3