Dermatology MCQ - Inflammatory Dermatoses - Linear IgA disease

A 7-year-old child is brought to clinic with a sudden onset of tense blisters and urticarial plaques on the trunk and extremities. Some blisters are noted to have a "cluster of jewels" or "string of pearls" appearance at the periphery of the plaques. The most specific diagnostic test to confirm the suspected diagnosis is:

A. Tzanck smear
B. Serum levels of desmoglein 1 and 3 antibodies
C. Direct immunofluorescence of perilesional skin
D. Potassium hydroxide (KOH) preparation of the roof of a blister
E. Patch testing

Correct Answer: C. Direct immunofluorescence of perilesional skin

Answer & Explanation

Explanation:

The presentation of tense blisters in a child with the characteristic "cluster of jewels" sign (a ring of vesicles or blisters at the edge of an urticarial plaque) is highly suggestive of Linear IgA Disease (LAD), which in children is often called Chronic Bullous Disease of Childhood.

• Key Diagnostic Test: The definitive diagnosis for all autoimmune blistering diseases is Direct Immunofluorescence (DIF) on a perilesional skin biopsy.

• Pathognomonic Finding in LAD: DIF shows linear deposition of IgA along the basement membrane zone. This is the diagnostic hallmark.

The other options are incorrect:

• A. Tzanck smear: This is used to detect multinucleated giant cells in herpes virus infections (e.g., HSV, VZV) and is not specific for autoimmune blistering diseases.

• B. Serum levels of desmoglein 1 and 3 antibodies: These are the specific serologic tests for pemphigus vulgaris and pemphigus foliaceus. They are not relevant for Linear IgA disease.

• D. Potassium hydroxide (KOH) preparation: This is used to diagnose fungal infections (tinea), which do not present with widespread tense blisters.

• E. Patch testing: This is used to diagnose allergic contact dermatitis, a type IV delayed hypersensitivity reaction, not an autoimmune blistering disorder.

Key Associations for Linear IgA Disease

• Pathophysiology: An autoimmune subepidermal blistering disorder characterized by the presence of IgA autoantibodies directed against various components of the basement membrane zone (e.g., LAD-285, BP180).

• Clinical Presentation:

  • Adults: Can present similarly to bullous pemphigoid or dermatitis herpetiformis, with tense blisters on urticarial plaques.

  • Children (Chronic Bullous Disease of Childhood): Often has a more acute onset. The "string of pearls" or "cluster of jewels" sign is a highly characteristic, though not always present, feature. Mucosal involvement (oral, conjunctival) can occur.

• Drug-Induced LAD: A significant number of cases in adults are triggered by medications, most commonly vancomycin. Other drugs include NSAIDs, penicillins, and captopril.

• Differential Diagnosis: Includes bullous pemphigoid (IgG deposition on DIF), dermatitis herpetiformis (granular IgA deposition in the dermal papillae, associated with celiac disease), and bullous lupus.

• Histopathology: Shows a subepidermal blister with a neutrophilic infiltrate in the dermal papillae, which can be histologically indistinguishable from dermatitis herpetiformis.

• Prognosis:

  • In children, the disease often undergoes spontaneous remission around puberty.

  • In adults, the course is more chronic but is generally responsive to treatment.

• Management:

  • First-line: Dapsone is the treatment of choice due to its specific anti-neutrophilic effect. The dose is titrated based on clinical response and monitoring for hemolytic anemia (check G6PD level prior to initiation).

  • Second-line: Systemic corticosteroids (prednisone) can be used initially for rapid control or in combination with dapsone.

  • Other Agents: For refractory cases, sulfapyridine, colchicine, or immunosuppressants like azathioprine or mycophenolate mofetil may be used.

  • Drug-induced Cases: The cornerstone is identification and discontinuation of the offending medication.