๐ ็ธฝ็ฎ้ ๏ฝ ๐ ่ฑๆๅๆ๏ผๆฌ็ฏ๏ผ ๏ฝ ๐ ๅฎๆด็ฟป่ญฏ ๏ฝ โญ ็ฒพ่ฏ็ญ่จ
Papular urticaria
Papular urticaria
Clinical features Although papular urticaria (prurigo mitis) is often described as a variant of urticaria, and the histologic picture is that of an urticarial dermatitis, the lesions are persistent and patients do not fulfill the criteria for the diagnosis of urticaria. In the latter, lesions are self-limited even in cases of chronic urticaria. The condition is generally regarded as a variant of an insect bite reaction.1โ4 Papular urticaria has no sex predilection, and although the age range is wide, it tends to be more frequent in children. It presents as small, itchy, red papules that tend to appear in crops. Most lesions are no more than a few millimeters in diameter but larger lesions may be seen. They are more usually seen on exposed areas of the body and tend to be more prevalent during the summer months. Changes secondary to scratching including excoriations are frequent. There are no associations with systemic disease.
A
Pathogenesis and histologic features The pathogenesis is not entirely clear, but it is generally believed that the condition is triggered by a hypersensitivity reaction to insect or arthropod bites.5,6 Many insects and arthropods have been implicated in the disease including fleas, carpet beetles, lice, bedbugs, mosquitoes, and even caterpillars. This is further supported by the rash clearing after the patient returns from holidays or after moving to a new house. A study found evidence of IgG against bedbugs (Cimex lectularius) in affected patients, suggesting a role in the pathogenesis of the disease.6 In papular urticaria related to flea bites, patients appear to react to a variety of low molecular weight antigens derived from fleas.7,8 Patients with papular urticaria secondary to fleas may be related to an aberrant T-helper (Th17) response and increased production IL-10. This may be related to an impaired dendritic cell response in these patients.9
The histologic features are fairly non-specific. In intact lesions, the epidermis is unremarkable or slightly acanthotic. Changes of excoriation may be evident. In the dermis there is a mild to moderate, superficial, and deep, often wedge-shaped, mainly perivascular inflammatory cell infiltrate composed of lymphocytes, histiocytes, and eosinophils.7 Neutrophils can be seen in some cases.10 A few CD30-positive lymphocytes are sometimes present.