2. A 16-year-old high school student joins her friends in a 2K run one morning. The next day, her shins are so painful she can hardly walk. She applied ice packs to her legs, using elastic bandages to hold them in place until the ice cubes melt. As her legs rewarm, a rash appears where the ice packs contacted the skin.
Diagnosis: This condition is urticarial in nature—albeit an unusual form, triggered by cold. Though it appears counterintuitive, cold uriticaria typically appears only on rewarming of the affected area and is marked by the sudden appearance of “welts” or “hives” that usually clear (with or without treatment) within hours.
Uncomplicated urticaria resolves without leaving any signs (eg, purpura, ecchymosis) that might otherwise suggest the presence of a vasculitic component, such as that seen with lupus or other autoimmune diseases. Blanchability on digital pressure is one way to confirm benignancy, since blood tends to leak from vessels damaged by vasculitis, emptying into the surrounding interstitial spaces and presenting as nonblanchable petechiae, purpura, or ecchymosis. The relatively benign nature of this patient’s urticaria was also suggested by additional history taking, in which she denied having fever, malaise, or arthralgia. These are all symptoms we might have seen with more serious underlying causes.
Cold urticaria is one of the so-called physical urticarias, a group that includes urticaria caused by vibration, pressure, heat, sun, and even exposure to water. Thought to comprise up to 20% of all urticarias, the physical urticarias occur most frequently in persons ages 17 to 40. Dermatographism is the most common form, occurring in the linear track of a vigorous scratch as a wheal that manifests rapidly, lasts a few minutes, then disappears without a trace. Its presence is purposely sought by the examiner to confirm the diagnosis of urticaria (most often the chronic idiopathic variety).
For more information, see “Inexperienced runner develops leg rash.” Clin Rev. 2012;22(8):W3