CU lesions are swollen pink or red wheals, of variable size, often with surrounding redness. They are generally itchy rather than painful or burning. Angioedema is not itchy, brawny, of a non-pitting quality with indistinct margins and without redness.
There are a number of chronic urticaria and angioedema (CU) subsets that are triggered by environmental sources. These are called physical urticarias.
In aquagenic urticaria, patients develop hives after contact between water and the skin. Temperature is not a factor in this type of urticaria. The hives are generally “pinpoint”, measuring 1-3mm. This is confirmed by applying a water compress at near body temperature to the skin of the upper body for 30 minutes.
Cholinergic urticaria also causes pinpoint hives, but these hives are surrounded by large flare reactions as a result of increased body temperature. Exercise, sweating, emotional stress, hot baths and showers are all frequent triggers of this subtype. Cholinergic urticaria can be benign or life threatening. Testing involves exercise or hot water immersion as these activities raise the core body temperature.
Cold urticaria results in hiving when the skin is exposed to a cold source. Patients may have systemic reactions in the event of full body exposure to the cold (swimming in cold water, etc). This is tested by placing an ice cube on the patient’s skin and waiting for a reaction, which occurs when the skin starts to warm.
Delayed pressure urticaria/angioedema presents as swelling, which may be painful, after the skin is exposed to pressure. While 4-6 hours is a more typical duration for symptoms to present, in some patients it can take 12-24 hours. Working with tools, sitting on a bench, wearing tight clothing, and carrying a heavy purse are all representative triggers. Testing for this subtype involves placing a 15 lb weight on the patient’s shoulder for 10-15 minutes, then waiting for response. Angioedema at the site that evolves following this test is considered a positive test, regardless of whether or not weals are present. This type can be difficult to treat.
Dermatographia is the most common type of physical urticaria. 2-5% of the general population have dermatographia. Stroking the skin firmly causes a weal and flare reaction where the skin was touched. It does not usually require treatment.
Exercise induced anaphylaxis has two types: those in whom anaphylaxis in provoked strictly by exercise, and those in whom anaphylaxis is triggered when a specific food is consumed prior to exercise. Cholinergic urticaria can also be triggered by exercise, so it is important to distinguish between the two. Exercise anaphylaxis can only be triggered by exercise, whereas cholinergic urticaria results if the patient becomes too hot. People with exercise induced anaphylaxis need to carry epipens and must not exercise alone as reactions can be severe.
Solar urticaria is the development of hives when the skin is exposed to sunlight, generally within minutes. Solar urticarial is further divided in subtypes based upon which wavelengths of light are triggering to the patient. Testing involves lightbox exposure to isolated wavelengths of light. It is distinct from polymorphous light eruption, in which onset is often delayed and can last for days. It can cause papules, papulovesicles and plaque manifestations on the skin.
Recall urticaria is hiving at the site of a previous sting or injection when exposed again to the same trigger.
Vibratory angioedema causes itching and swelling when the skin is exposed to a vibration source. This specific type can show a familial trait. It is confirmed by showing a response after use of a vortex mixer (a piece of lab equipment that mixes solutions in tubes).
Jonathan A. Bernstein, et al. The diagnosis and management of acute and chronic urticaria: 2014 update. J Allergy Clin Immunol Volume 133, Number 5.
Usmani N,Wilkinson SM. Allergic skin disease: investigation of both immediate and delayed-type hypersensitivity is essential. Clin Exp Allergy 2007;37:1541-6.
Zuberbier T, Maurer M. Urticaria: current opinions about etiology, diagnosis and therapy. Acta Derm Venereol 2007;87:196-205.