Random Dermatology MCQ - Dermatitis Herpetiformis (DH)

A 30-year-old man presents with intensely pruritic grouped vesicles and papules on his elbows, knees, and buttocks. The lesions are symmetrically distributed. He also reports intermittent diarrhea. A skin biopsy of a new vesicle shows neutrophilic microabscesses in the dermal papillae. Direct immunofluorescence of perilesional skin is most likely to reveal which of the following patterns?

A) Linear IgA deposition along the basement membrane zone
B) Granular IgA deposition in the dermal papillae
C) Intercellular IgG deposition throughout the epidermis
D) Linear IgG and C3 deposition along the basement membrane zone
E) Shaggy deposition of IgA along the basement membrane zone

Correct Answer: B) Granular IgA deposition in the dermal papillae

Explanation

This patient has dermatitis herpetiformis (DH), a chronic, intensely pruritic autoimmune blistering disorder that is the cutaneous manifestation of celiac disease.

Key Diagnostic Features:

1. Clinical:

   • Symmetrical grouping of vesicles, papules, and excoriations on extensor surfaces (elbows, knees, buttocks, scalp). The intense pruritus often leads to patients excoriating the vesicles before they can be seen, leaving only erosions and crusts.

   • Associated with gluten-sensitive enteropathy (celiac disease), though gastrointestinal symptoms like diarrhea may be mild or absent.

2. Histopathology:

   • Neutrophilic microabscesses in the dermal papillae are the hallmark finding. Subepidermal blister formation occurs as these microabscesses coalesce.

3. Immunopathology:

   • Direct immunofluorescence (DIF) of perilesional skin is diagnostic. It shows granular deposits of IgA in the dermal papillae. This is the most specific test for DH.

   • Circulating antibodies against anti-tissue transglutaminase (tTG) and anti-endomysial antibodies are typically present and correlate with the degree of intestinal involvement.

Why Not Other Options?

• (A) Linear IgA deposition: This is the characteristic finding of Linear IgA disease.

• (C) Intercellular IgG: This is the hallmark of pemphigus vulgaris.

• (D) Linear IgG and C3: This is diagnostic for bullous pemphigoid.

• (E) Shaggy IgA deposition: This pattern is seen in epidermolysis bullosa acquisita.

Management:

• First-line: Dapsone. It provides rapid symptomatic relief of pruritus, often within 24-48 hours.

• Long-term management: A strict, lifelong gluten-free diet. This is essential for controlling the underlying celiac disease and often reduces or eliminates the need for dapsone over time.

Prognosis: Excellent with strict adherence to a gluten-free diet, which controls both the skin disease and prevents the long-term complications of celiac disease (e.g., lymphoma, osteoporosis).