Dermatology MCQ - Inflammatory Dermatoses - Lichen planus pemphigoides

A 45-year-old man with a several-month history of severe, classic lichen planus develops a sudden eruption of widespread, tense bullae on both his lichenoid papules and on previously unaffected, erythematous skin. A biopsy of a bulla from uninvolved skin is most likely to reveal which of the following histopathological findings?

A. Suprabasal acantholysis with tombstoning of basal keratinocytes
B. Subepidermal blister with eosinophils and linear deposition of IgG/C3 at the basement membrane zone
C. Subepidermal blister with neutrophils and microabscesses in the dermal papillae
D. Hypergranulosis, saw-toothing of the rete ridges, and a band-like lymphocytic infiltrate
E. Intraepidermal pustule with neutrophils and acantholysis

Correct Answer: B. Subepidastal blister with eosinophils and linear deposition of IgG/C3 at the basement membrane zone

Explanation

Lichen planus pemphigoides (LPP) is an autoimmune blistering disorder characterized by the coexistence of typical lichen planus and a bullous pemphigoid (BP)-like eruption. It is believed that the chronic inflammatory damage from lichen planus exposes hidden basement membrane zone antigens (most commonly the BP180 antigen), triggering a separate autoimmune response that results in blistering.

• Histopathology of the Bulla: A biopsy taken from a tense bulla on uninvolved or erythematous skin is crucial for diagnosis. The histology will show features of bullous pemphigoid: a subepidermal blister with a superficial dermal inflammatory infiltrate that contains a prominent number of eosinophils. This is distinct from the histology of the lichen planus lesions themselves.

• Direct Immunofluorescence (DIF): The confirmatory test is DIF on perilesional skin, which shows linear deposition of IgG and C3 along the basement membrane zone, identical to the finding in classic bullous pemphigoid.

Why other options are incorrect

• A. Suprabasal acantholysis with tombstoning of basal keratinocytes: This is the classic histopathological finding in pemphigus vulgaris.

• C. Subepidermal blister with neutrophils and microabscesses in the dermal papillae: This describes the histology of dermatitis herpetiformis or Linear IgA Disease, not LPP.

• D. Hypergranulosis, saw-toothing of the rete ridges, and a band-like lymphocytic infiltrate: This is the classic histology of a lichen planus papule. However, the question specifically asks for the finding from a bulla on uninvolved skin, which would not show these features.

• E. Intraepidermal pustule with neutrophils and acantholysis: This is characteristic of pemphigus foliaceus or subcorneal pustular dermatosis.

Key Associations for Lichen Planus Pemphigoides (LPP)

• Pathogenesis: Considered an "epitope spreading" phenomenon. The initial T-cell mediated attack in lichen planus damages the basal layer, revealing sequestered antigens like BP180 (and less commonly BP230). This leads to a subsequent B-cell response and autoantibody production, causing a BP-like clinical picture.

• Clinical Presentation: Patients first develop classic, pruritic, violaceous, polygonal papules of lichen planus. Weeks to months later, they develop a sudden eruption of tense bullae, which can arise on top of the existing lichen planus lesions (a highly suggestive sign) as well as on normal-appearing skin.

• Differential Diagnosis: The main differential is bullous lichen planus, where blistering occurs only within the pre-existing lichen planus plaques due to severe basal cell damage (Max-Joseph spaces). In bullous lichen planus, DIF is negative for linear IgG/C3 and shows the shaggy fibrinogen pattern typical of LP.

• Diagnosis: Diagnosis is confirmed by the combination of:

  1. Clinical findings of both LP and a BP-like eruption.

  2. Histology from a bulla showing subepidermal split with eosinophils.

  3. DIF showing linear IgG and/or C3 at the BMZ.

  4. Circulating anti-BMZ antibodies (often against BP180) on ELISA or IIF.

• Management: Treatment is more aggressive than for lichen planus alone. Systemic corticosteroids are first-line. Steroid-sparing agents like dapsone, tetracyclines, or more potent immunosuppressants like azathioprine or mycophenolate mofetil are often required. The prognosis is generally good with treatment, and the condition may eventually go into remission.