Q. A patient with intense itchy vesicular lesion on extensor surface presents with history of gluten senstivity. Likely diagnosis?

Explanation

## Correct Answer: D. Dermatitis herpetiformis Dermatitis herpetiformis (DH) is a chronic autoimmune blistering disorder pathognomonic for **celiac disease** (gluten-sensitive enteropathy). The discriminating feature here is the **combination of intense pruritus with vesicular lesions on extensor surfaces (elbows, knees, buttocks, shoulders) AND a documented history of gluten sensitivity**. DH is caused by IgA antibodies against tissue transglutaminase (tTG) in the dermal–epidermal junction, triggered by gluten ingestion. The intense itching (often described as burning) is characteristic and often precedes visible lesions by hours. Histologically, microabscesses of neutrophils are seen at the dermal–epidermal junction. Approximately 75–80% of DH patients have subclinical or clinical celiac disease on small-bowel biopsy, even if asymptomatic. The gold standard for diagnosis is **direct immunofluorescence (DIF) showing granular IgA deposits at the dermal–epidermal junction**. Treatment involves a gluten-free diet (definitive) and dapsone for symptomatic relief. In Indian practice, DH is less common than in Caucasian populations but should be suspected in any patient with this classic triad: extensor vesicles, intense pruritus, and gluten sensitivity. ## Why the other options are wrong **A. Psoriasis** — Psoriasis presents with erythematous plaques with silvery scale, not vesicles. While it can occur on extensor surfaces, it lacks the intense pruritus and vesicular morphology. Psoriasis is not associated with gluten sensitivity. The lesions are chronic and scaly, not acute and blistering. **B. Bullous pemphigoid** — Bullous pemphigoid presents with large, tense bullae (not small vesicles) on flexor surfaces and lower abdomen, not extensor surfaces. It is an autoimmune disease against BP180/BP230 (basement membrane), not gluten-related. DIF shows **linear** IgG and C3 at the basement membrane zone, not granular IgA. No association with celiac disease. **C. Pemphigus vulgaris** — Pemphigus vulgaris presents with flaccid bullae and erosions, often starting intraorally, with positive Nikolsky sign. It is an autoimmune disease against desmoglein 3 (mucosal) and desmoglein 1 (cutaneous). DIF shows **intercellular** IgG deposits, not granular IgA. No gluten association. Lesions are intraepidermal, not subepidermal. ## High-Yield Facts - **Dermatitis herpetiformis = celiac disease until proven otherwise**: 75–80% have biopsy-proven celiac disease; gluten-free diet is curative. - **Extensor surfaces (elbows, knees, buttocks, shoulders)** are the classic sites; intense pruritus often precedes visible lesions. - **Direct immunofluorescence (DIF) shows granular IgA deposits at the dermal–epidermal junction** — this is the diagnostic gold standard. - **Dapsone** is the first-line symptomatic treatment; sulfapyridine is an alternative; gluten-free diet addresses the root cause. - **Microabscesses of neutrophils** at the dermal–epidermal junction on histology distinguish DH from other blistering disorders. - **IgA antibodies against tissue transglutaminase (tTG)** are the pathogenic mechanism; serology (anti-tTG IgA) supports diagnosis. ## Mnemonics **DH = Dermatitis + Herpetiformis = Gluten** **D**ermatitis **H**erpetiformis → **D**apsone + **D**iet (gluten-free). Remember: **Extensor** surfaces, **Intense itch**, **IgA** on DIF, **Celiac** disease. **DH vs BP vs PV — DIF Pattern** DH = **Granular IgA** (dermal–epidermal junction). BP = **Linear IgG** (basement membrane). PV = **Intercellular IgG** (acantholysis). Use DIF to distinguish. ## NBE Trap NBE may pair "vesicular lesion" with pemphigus or bullous pemphigoid to distract from the **gluten sensitivity** clue, which is the pathognomonic trigger for DH. Students who ignore the gluten history will choose a non-gluten-associated blistering disorder. ## Clinical Pearl In Indian clinical practice, always ask about gastrointestinal symptoms (chronic diarrhea, malabsorption, weight loss) and dietary history in any patient with extensor vesicles and severe pruritus. A gluten-free diet trial can be both diagnostic and therapeutic; improvement in skin lesions within weeks strongly supports DH and underlying celiac disease. _Reference: Robbins & Cotran Pathologic Basis of Disease, Ch. 25 (Skin); Harrison's Principles of Internal Medicine, Ch. 52 (Dermatological Manifestations of Internal Disease)_