Precipitating causes:
(1) exercise
(2) anxiety
(3) sweating
(4) passive warming (in a hot shower, bath or the sauna)
The skin lesions may develop within 2-30 minutes of the precipitating cause.
Clinical features:
(1) The urticarial lesions are pruritic and tend to be smaller than usual urticaria, with a diameter of 1-4 mm ("punctate").
(2) Lesions usually begin on the face and neck then can spread to other parts of the body.
(3) Vascular collapse and hypotension are uncommon.
(4) Patients have signs of cholinergic stimulation such as lacrimation, salivation, abdominal cramps, and diarrhea.
(5) Systemic symptoms may include headache, dizziness, wheezing and syncope.
Laboratory findings:
(1) Plasma histamine levels are increased as urticaria develop.
Confirmatory tests may be insensitive or nonspecific, especially when mixed:
(1) Intradermal injection of a cholinergic agent such as metacholine induces wheals in only 30-50% of patients.
(2) warm bath for 10-20 minutes
(3) exercise
Differential diagnosis:
(1) exercise-induced anaphylaxis (not induced by a warm bath)
