Annular urticaria is commonly misdiagnosed as erythema multiforme. The two are readily distinguished by the evanescent and migratory nature of urticaria, associated pruritus, response to antihistamines, and lack of epidermal necrosis. Both tinea corporis and psoriasis commonly present with annular lesions; however, unlike urticaria, both conditions demonstrate epidermal change in the form of surface scale. Any scaly dermatosis warrants a potassium hydroxide examination to rule out the possibility of tinea. When no scale exists, tinea and psoriasis are unlikely.
Urticaria commonly follows an upper respiratory tract infection and is likely related to the transient production of antibodies that cause mast cell degranulation. The most important differential diagnosis is urticarial vasculitis, which is typically a presenting manifestation of smoldering systemic lupus erythematosus. In contrast to urticaria, the lesions of urticarial vasculitis are fixed in position for longer than 24 hours, often burn more than they itch, and heal with bruising or pigmentary change.
A biopsy establishes the diagnosis. Urticaria is characterized by neutrophils within the vascular lumen. Over time, the neutrophils travel to the perivascular area and are joined by eosinophils, but karyorrhexis (nuclear fragmentation) is notably absent. In contrast, a biopsy of urticarial vasculitis commonly demonstrates expansion of the vessel wall with fibrin deposition, karyorrhexis, and erythrocyte extravasation.
Urticaria usually lasts less than 5 weeks. Cases that persist beyond 5 weeks are more likely to be autoimmune, with an immunoglobulin (Ig) G that binds the IgE receptor. Such cases often persist for years and require immunosuppressive medication for control. In contrast, transient urticaria often responds well to antihistamine therapy. Nonsedating antihistamines are preferred, especially for those who must drive. It is common for patients to require higher than the usual labeled dose. Prednisone may be required in refractory cases of acute urticaria; however, it has no place in the management of chronic urticaria because the disease will relapse as soon as therapy is discontinued, and prednisone is not suitable for long-term use. Refractory disease may respond to tricyclic medications such as doxepin, immunosuppressive medication, or omalizumab, a monoclonal antibody.[1,2,3,4]
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Cite this: Dirk M. Elston. An Anxious Hiker With Recurring Annular Rash and Sleep Loss - Medscape - Jan 26, 2022.