Dermatology MCQ - Inflammatory Dermatoses - Pathophysiology of urticarial vasculitis

A skin biopsy from a patient with urticarial lesions that are painful, last for more than 24 hours, and resolve with residual purpura would most likely demonstrate which of the following as the primary histopathologic finding?

A. Sparse perivascular infiltrate of lymphocytes and eosinophils with dermal edema
B. Neutrophilic infiltration with leukocytoclasia (nuclear dust) and fibrinoid deposits around venules
C. Epidermal spongiosis and a superficial perivascular lymphocytic infiltrate
D. Dermal deposits of mucin with a perivascular and periadnexal lymphocytic infiltrate
E. Subepidermal blister with eosinophil-rich infiltrate

Correct Answer: B. Neutrophilic infiltration with leukocytoclasia (nuclear dust) and fibrinoid deposits around venules

Answer & Explanation

Explanation:

Urticarial vasculitis (UV) is fundamentally a small-vessel leukocytoclastic vasculitis. The clinical description provided—painful, long-lasting lesions with residual purpura—is classic for UV and distinguishes it from simple urticaria.

The hallmark histopathologic features reflect this inflammatory damage to blood vessels:

• Neutrophilic Infiltration: The dermal infiltrate is predominantly composed of neutrophils, unlike the lymphocytic and eosinophilic infiltrate of common urticaria.

• Leukocytoclasia: This refers to the fragmentation of neutrophil nuclei, resulting in "nuclear dust" around the vessels. It is a key diagnostic feature of leukocytoclastic vasculitis.

• Fibrinoid Deposits: There is deposition of brightly eosinophilic fibrin within and around the walls of the postcapillary venules, indicating vessel wall injury and necrosis.

• Extravasated Erythrocytes: Red blood cells are seen outside the vessels, which correlates clinically with the purpuric or bruise-like appearance.

The other options are histologic findings for other conditions:

• A. Sparse perivascular infiltrate of lymphocytes and eosinophils with dermal edema: This is the classic histology of common urticaria.

• C. Epidermal spongiosis and a superficial perivascular lymphocytic infiltrate: This is characteristic of spongiotic dermatitis, such as eczema.

• D. Dermal deposits of mucin with a perivascular and periadnexal lymphocytic infiltrate: This describes lupus erythematosus or other connective tissue diseases.

• E. Subepidermal blister with eosinophil-rich infiltrate: This is the classic finding in bullous pemphigoid.

Key Associations for Urticarial Vasculitis

• Pathophysiology: UV is an immune complex-mediated disease. Circulating immune complexes deposit in the postcapillary venules, activating the complement cascade and attracting neutrophils, which release proteolytic enzymes and reactive oxygen species that damage the vessel wall.

• Clinical Presentation: The key to suspecting UV is the deviation from common urticaria: lesions are often painful or burning rather than purely pruritic, individual wheals persist for >24 hours, and they resolve with ecchymosis, purpura, or hyperpigmentation. Systemic symptoms are common.

• Differential Diagnosis: The main differential is chronic spontaneous urticaria. Other vasculitides (e.g., IgA vasculitis), cryoglobulinemia, and Schnitzler syndrome (UV, monoclonal gammopathy, fever) must be considered.

• Prognosis & Associations: UV can be an isolated skin condition or a cutaneous marker of a systemic disease. It is strongly associated with:

  • Connective tissue diseases (particularly SLE and Sjögren's syndrome)

  • Infections (hepatitis B and C)

  • Serum sickness

  • Paraproteinemias (e.g., IgM gammopathy)

• Management: Investigation for underlying systemic disease is mandatory. Treatment is more complex than for common urticaria and may require systemic corticosteroids, dapsone, colchicine, or other immunosuppressants.