Differential Diagnosis: Vesiculobullous Disorders
Blistering disorders are classified by the level of split in the skin (intraepidermal vs. subepidermal). Accurate diagnosis relies on clinical presentation, Nikolsky sign, and immunofluorescence.
Key Diagnostic Table
| Disease | Level of Split | Key Features |
|---|---|---|
| Pemphigus Vulgaris | Intraepidermal (Suprabasal) | Mucosal involvement common; Flaccid bullae; Positive Nikolsky. |
| Bullous Pemphigoid | Subepidermal | Elderly patients; Tense bullae; Mucosal involvement rare; Negative Nikolsky. |
| Dermatitis Herpetiformis | Subepidermal | Intensely pruritic; Extensor surfaces; Associated with Celiac disease. |
Examining the Blister
- Nikolsky Sign: Positive in Pemphigus Vulgaris (the skin shears off easily with lateral pressure because the cells lack adhesion).
- Immunofluorescence (IF):
- Pemphigus Vulgaris: “Net-like” (fishnet) pattern of IgG/C3 in intercellular spaces.
- Bullous Pemphigoid: “Linear” band of IgG/C3 at the dermo-epidermal junction.
High-Yield Exam Pearl:
- Mnemonic: Pemphigus = under the surface (intra-epidermal); Pemphigoid = over the basement membrane (sub-epidermal).
- Celiac Link: Always connect Dermatitis Herpetiformis to Gluten-Sensitive Enteropathy (Celiac disease).