ABSTRACT (233/250)
Background: Cold urticaria (ColdU) is a common type of chronic
inducible urticaria. Patients with typical ColdU develop wheals in
response to standard cold stimulation tests (CSTs), an ice cube (ICT) or
TempTest®. As of now, the evaluation of CST response
is visual and subjective. Validated, robust, and objective test readouts
lacking today are needed.
Methods: We subjected 63 patients (39 with typical ColdU and 24
with atypical ColdU) and 15 healthy controls (HCs) to
TempTest® CSTs and critical temperature threshold
assessments. Blood microcirculation photoplethysmography (PPG)
measurements were performed 5 min before and 10 min after the ICT on the
volar forearm.
Results: PPG amplitudes reflected normal baseline skin blood
perfusion in patients with typical or atypical ColdU. Ice cube CSTs
induced a marked increase in blood perfusion and PPG amplitudes in
typical but not atypical ColdU, with distinct pre-post CST changes in
PPG amplitudes in the former. The ratio of post-provocation and baseline
PPG amplitudes (R PPG) in typical ColdU patients
exceeded that in atypical ColdU patients and HCs more than 3-fold.
Almost all typical ColdU patients (98%), but only 13% of atypical
ColdU patients and 7% of HCs had R PPG>3. PPG results matched those of CSTs in 94% of all tested
individuals.
Conclusion: Photoplethysmographic assessments of CST responses
appear accurate and provide objective readouts. PPG may be of use in
diagnosing ColdU, distinguishing typical and atypical ColdU, and more
precise threshold testing.
Keywords: cold urticaria, image processing, non-invasive
diagnostics, photoplethysmography, skin inspection