Diagnosis of cholinergic urticaria (ChU) often depends on provocation tests.
Traditional treatment options (antihistamines, leukotriene inhibitors, and immunosuppressives) may not be effective in refractory ChU patients. Demonstration of immediate hypersensitivity to autologous sweat skin testing (ASwST) may provide a rationale for use of omalizumab (Xolair).
Patients with severe ChU may have difficulty producing sufficient quantities of sweat for ASwST due to the fact that the effort to produce the sweat sample may cause an exacerbation of ChU.
As an alternative, generation of sweat by iontophoresis with pilocarpine can be performed, using the same method applied in the sweat test for CF diagnosis.
Pilocarpine is a muscarinic alkaloid obtained from the leaves of tropical American shrubs from the genus Pilocarpus.
Iontophoresis is a non-invasive method of propelling high concentrations of a charged substance (medication) transdermally by repulsive electromotive force using a small electrical charge applied to an iontophoretic chamber containing a similarly charged active agent.
In this case report, the patient had a positive ASwST. The testing methods were validated by negative ASwST, saline control, and positive histamine control in a nonurticarial control patient.
The patient started treatment with omalizumab and by the second injection, her quality of life score was improved, as were daily medication use and exercise tolerance.
A case of severe refractory chronic urticaria: A novel method for evaluation and treatment. Otto, Hans F.; Calabria, Christopher W. Allergy and Asthma Proceedings, Volume 30, Number 3, May/June 2009 , pp. 333-337(5).
Image source: Pilocarpine, Wikipedia, public domain.