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AT-A-GLANCE

AT-A-GLANCE

  • An uncommon form of chronic inducible urticaria

  • Erythema and itchy wheals occur within minutes of sunlight exposure and resolve within hours.

  • May be disabling and, rarely, life threatening.

  • Phototesting confirms the diagnosis, determines the trigger threshold, and identifies the eliciting wave lengths.

  • Sensitivity may be to ultraviolet B, ultraviolet A, visible light, and/or any combination, but most commonly to ultraviolet A and visible light.

  • Sunlight avoidance, high–protection factor broad-spectrum sunscreens, and antihistamines may help.

  • Omalizumab may be a helpful second-line treatment

  • Phototherapy may also help but is usually not feasible as long-term treatment

INTRODUCTION

DEFINITIONS

Solar urticaria (SolU) is defined by the appearance of a whealing response within minutes of exposure to sunlight.1 SolU is a rare type of physical urticaria. Physical urticarias, together with cholinergic urticaria, contact urticaria, and aquagenic urticaria, are subforms of chronic inducible urticaria, one of the 2 forms of chronic urticaria, the other one being chronic spontaneous urticaria. SolU usually is primary, where the cause is unknown. Very rarely, SolU is linked to cutaneous porphyria or systemic lupus erythematosus (SLE) and is then termed secondary SolU.

HISTORICAL PERSPECTIVE

Chronic inducible urticaria and their characteristic features, that is, wheal responses at skin sites exposed to urticariogenic triggers, were first described by Hippocrates.2 The first reports of SolU are from the 18th century, and in 1887, SolU was identified as being sunlight-dependent.3,4

EPIDEMIOLOGY

The prevalence of SolU is low, but conclusive prevalence data are missing. It has been estimated that 3 in 100,000 are affected.5 SolU reportedly accounts for 7% of all photodermatoses6 and for less than 0.5% of all chronic urticaria cases.7 SolU predominantly affects women in the third decade of life. Most patients show symptoms perennially, some only during spring to autumn.5

CLINICAL FEATURES

CUTANEOUS FINDINGS

SolU is characterized by erythema and itchy wheals that develop rapidly at skin sites exposed to sun or artificial light (Fig. 96-1). Light-exposed skin first shows diffuse erythema, followed by whealing associated with itch and/or, less frequently, burning and stinging. Wheals in SolU generally develop within a few minutes up to 1 hour of exposure and disappear usually within 1 hour and after a maximum of 24 hours of cessation of exposure, without leaving visible changes of the skin. SolU typically affects skin areas that are normally shielded by clothing and it spares skin sites that are frequently exposed to light such as the hands and the face, presumably because chronically sun-exposed areas show “hardening” or tolerance. SolU patients typically experience their first signs and symptoms after prolonged sun exposure on the first sunny days in spring. Rare variants include fixed SolU, which is characterized by the reoccurrence of light-induced whealing in the ...

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