Urticaria and mimickers of urticaria

Urticaria is a common skin condition encountered across various specialties in medicine, especially in dermatology and allergy/immunology practice. It has a heterogeneous presentation hence it is unsurprising that many skin conditions may be confused with urticaria. Urticaria may present as acute or chronic urticaria, the latter can be further categorised into chronic spontaneous and chronic inducible. In this article, we explore, explain, and summarise various skin lesions that are considered mimickers of urticaria, to promote understanding of each of the conditions highlighted, improve recognition, and reduce misdiagnosis.

The Sting of a White Flannel Moth Caterpillar (Novape ovina)

The purpose of this report is to describe a case of urticarial dermatitis, or erucism, caused by the white flannel moth caterpillar (Norape ovina) in central Virginia. Many caterpillars are known to cause erucism, with the puss caterpillar (Megalopyge opercularis) being the most reported culprit in the United States. White flannel moth caterpillars are expected to cause erucism as they belong to the same family as the puss caterpillar (Megalopygidae) and have similar venom-containing hairs, but no reports of the reaction or clinical course have been documented in the medical literature. A subject was stung by a white flannel moth caterpillar after it fell on his neck while clearing brush with a machete. The subject experienced immediate pain and developed a raised, erythematous rash where the caterpillar had fallen. The rash, referred to as erucism, was painful for 1 d and improved slowly over the course of 2 wk, but a small area of discoloration remained 2.5 mo after contact. Symptoms were managed by the subject at home and no medications were administered. The white flannel moth caterpillar inflicts erucism similar to that caused by the more commonly mentioned puss caterpillar. If only local symptoms are sustained from contact with a white flannel moth caterpillar, it can be safely and effectively managed with over-the-counter medications similar to the management for erucism induced by other caterpillar species. Irrigation and removal of urticating hairs with adhesive tape may help reduce the pain and is recommended, though not performed in this case.

Mycophenolate mofetil as a treatment for urticarial dermatitis

We report two cases of adults with urticarial dermatitis who could not be managed by a variety of treatments but who obtained good control with mycophenolate mofetil (MMF). A clinical response was seen 6-8 weeks from treatment onset and they were maintained on MMF 1 g twice daily (case 1), and MMF 1 g omni mane and 500 mg omni nocte (case 2), with no major exacerbations for many years. MMF is an immunosuppressive agent, which is currently used off-label for many dermatological conditions. To date, there have been no studies investigating the use of MMF as a treatment for urticarial dermatitis. The cases we present suggest that MMF is an effective treatment for this condition, and we recommend that MMF be considered as a treatment option.

Urticarial dermatitis: clinical features, diagnostic evaluation, and etiologic associations in a series of 146 patients at Mayo Clinic (2006-2012)

BACKGROUND

Few studies have examined patients initially presenting with clinical features of urticarial dermatitis (UD).

OBJECTIVE

We sought to examine clinical and laboratory evaluations and final diagnoses of patients with clinical features of UD.

METHODS

This was a retrospective review of patients with UD seen at Mayo Clinic between 2006 and 2012, and formal review of available skin biopsy specimens to identify any patients who also met microscopic criteria for UD.

RESULTS

Of 146 patients with clinical features of UD (mean age at onset, 60 years), 88 (60%) were female. The most common final diagnoses were: UD (70 patients [48%]); dermatitis not otherwise specified (24 [16%]); urticaria (14 [10%]); drug reaction (9 [6%]); bullous pemphigoid (6 [4%]); atopic dermatitis (5 [3%]); and contact dermatitis (4 [3%]). Of 40 patients with clinical and microscopic features of UD, 46% (16 of 35) had no response to treatment, whereas 10% (4 of 40) had a newly diagnosed concurrent malignancy (within 4 months of UD onset).

LIMITATIONS

This was a retrospective study.

CONCLUSION

Clinical features of UD occur in various dermatologic diseases. Some patients with clinical and microscopic features of UD have associated malignancies. Further studies should assess optimal evaluation and management of UD.

Retrospective chart review in a cohort of patients with urticarial dermatitis

Urticarial dermatitis is a poorly understood skin condition while it seems to be much more common than the paucity of reports suggest. It manifests with severely pruritic papules and plaques that resemble eczematous and urticarial lesions morphologically. The key clues to diagnosis are the urticarial appearance and overlap with an eczematous reaction. Here, we present a series of 19 cases (13 women and six men) with urticarial dermatitis clinically and histologically. The patients' average age was 58 and most of the cases were idiopathic. Trunk and proximal extremities were the most common sites involved followed by the distal extremities. Poor response to potent topical corticosteroids and antihistamines was usual and many patients required oral prednisone or other immunosuppressant agents or phototherapy.