Abstract
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.