Dermatology MCQ - Inflammatory Dermatoses - Chronic spontaneous urticaria

A 28-year-old woman presents with a 5-week history of recurrent, intensely pruritic wheals. The individual lesions appear suddenly, last for 4-6 hours, and resolve completely without bruising. She reports no associated fever, joint pain, or weight loss. Her only medication is an oral contraceptive pill, which she has been taking for 3 years. Physical examination during a flare is significant only for widespread urticarial wheals and excoriations. The most appropriate initial diagnostic step is:

A. Order a skin biopsy
B. Perform autologous serum skin testing (ASST)
C. Order a broad panel of laboratory tests including CBC, ESR, ANA, and thyroid function
D. Initiate a trial of a high-dose, non-sedating H1-antihistamine
E. Perform a blinded oral challenge to her contraceptive pills

Correct Answer: D. Initiate a trial of a high-dose, non-sedating H1-antihistamine

Answer & Explanation

Explanation:

This clinical presentation is classic for chronic spontaneous urticaria (CSU). The history of wheals that are transient (individual lesions lasting <24 hours), migratory, and pruritic, without systemic symptoms or signs of vasculitis, is highly characteristic.

According to national and international guidelines (e.g., EAACI/GA²LEN/EDF/WAO), the cornerstone of management for CSU is a stepwise approach starting with second-generation H1-antihistamines. If standard doses are ineffective after 1-2 weeks, the recommended next step is to increase the dose of the non-sedating H1-antihistamine up to fourfold.

• Why this is correct: Initiating or escalating antihistamine therapy is both a diagnostic and therapeutic step. A positive response supports the diagnosis of a non-vasculitic, histamine-driven process. Extensive and costly laboratory workups are not indicated in the absence of suggestive history or physical findings.

The other options are incorrect or not first-line:

• A. Order a skin biopsy: A biopsy is reserved for cases where urticarial vasculitis is suspected. Key clues for vasculitis include individual lesions lasting >24 hours, resolving with bruising or purpura, and associated pain or burning.

• B. Perform autologous serum skin testing (ASST): The ASST is a test for functional autoantibodies and is a marker for autoimmune CSU. It is a specialized test and is not part of the routine initial diagnostic workup. It may be considered in refractory cases.

• C. Order a broad panel of laboratory tests: Extensive laboratory testing in an otherwise healthy patient with a classic presentation of CSU has a very low yield and is not cost-effective. Testing should be guided by specific elements in the history (e.g., thyroid function tests if there is personal or family history of thyroid disease).

• E. Perform a blinded oral challenge to her contraceptive pills: While drugs can cause urticaria, her contraceptive pill is an unlikely trigger as she has been on it stably for years before the urticaria began. Drug challenge is not a routine initial test for CSU.

Key Associations for Chronic Spontaneous Urticaria

• Pathophysiology: In CSU, mast cells in the skin are activated through various immunologic (e.g., autoantibodies against IgE or the high-affinity IgE receptor) and non-immunologic mechanisms, leading to the release of histamine and other mediators.

• Differential Diagnosis: The main differential is urticarial vasculitis. Other conditions to consider include urticarial drug eruptions, cutaneous mastocytosis (urticaria pigmentosa), and autoinflammatory syndromes (which typically present with fever and elevated acute phase reactants).

• Prognosis: CSU is often self-limited, but the course can be unpredictable. Approximately 50% of patients experience remission within 1 year, but a significant proportion may have symptoms for years.

• Management (Stepwise):

  1. Step 1: Second-generation H1-antihistamines (standard dose).

  2. Step 2: Increase H1-antihistamine dose (up to 4x standard).

  3. Step 3: Add omalizumab (anti-IgE).

  4. Step 4: Consider cyclosporine or other immunosuppressants.