Role of thermoregulatory sweat test in the diagnosis of facial flushing: A retrospective case series
Authors: Rachel L. Ziebart, Elizabeth A. Coon, Julio C. Sartori-Valinotti
Journal: Journal of the American Academy of Dermatology (2023)

To the Editor: Facial flushing is a common complaint seen by dermatologists. One cause of flushing is cutaneous vasodilation as a mechanism to dissipate heat secondary to hyperthermia.1Wilkin J.K. The red face: flushing disorders.Clin Dermatol. 1993; 11: 211-223https://doi.org/10.1016/0738-081x(93)90057-jAbstract Full Text PDF PubMed Scopus (0) Google Scholar Hyperthermia can be seen in patients with anhidrosis or hypohidrosis, which is the loss of or impaired ability to sweat, respectively. Assessment of anhidrosis and/or hypohidrosis is challenging because patients are unlikely to notice and report a reduction in sweating.2Cheshire Jr., W.P. Thermoregulatory disorders and illness related to heat and cold stress.Auton Neurosci. 2016; 196: 91-104https://doi.org/10.1016/j.autneu.2016.01.001Abstract Full Text Full Text PDF PubMed Scopus (205) Google Scholar Thermoregulatory sweat test (TST) is useful to evaluate thermoregulatory and sweating functions. The aim of this study was to determine the frequency and severity of anhidrosis in patients with unexplained facial flushing, as measured by TST. During TST, the patient is covered in Alizarin-red indicator powder and warmed in a chamber to a thermoregulatory end point.2Cheshire Jr., W.P. Thermoregulatory disorders and illness related to heat and cold stress.Auton Neurosci. 2016; 196: 91-104https://doi.org/10.1016/j.autneu.2016.01.001Abstract Full Text Full Text PDF PubMed Scopus (205) Google Scholar In the areas of the body with normal sweating, the indicator powder changes color from yellow or gold to purple, allowing the examiner to calculate percentages of anhidrosis.3Carroll M.S. Reed D.W. Kuntz N.L. Weese-Mayer D.E. Novel methods of imaging and analysis for the thermoregulatory sweat test.J App Physio. 2018; 125: 755-762https://doi.org/10.1152/japplphysiol.01086.2017Crossref PubMed Scopus (4) Google Scholar The results of this test are standardized through the comparison of patient results with normative data. Less than 2% anhidrosis is considered a normal test, whereas greater than or equal to 2% is abnormal. Examples of TST results from this study are included in Fig 1. Those included in the study were patients aged 18 years and older who presented to Mayo Clinic between June 2018 and June 2022 with a complaint of facial flushing and who had completed TST. Patients who had a known explanation for facial flushing (such as sunburn) were excluded. Data were collected on age, sex assigned at birth, race, and menopausal status for all patients. Analysis was conducted in BlueSky Commercial Server Edition, version 7.40 using a 2-sample t-test for continuous variables and Fisher's exact test for categorical variables. The study was approved by the Mayo Clinic Institutional Review Board (#22-008060). From a total of 36 patients, there were 28 females and 8 males. Thirty-three identified as White, 1 Asian, 1 Asian Filipino, and 1 Asian Indian. Most patients (69%) had an abnormal TST result. Older age and female sex were significantly correlated with anhidrosis (P = .024; P = .040). Higher prevalence of anhidrosis was seen in postmenopausal women, which was an expected finding given the higher age of postmenopausal women. Menopausal status alone was not significantly correlated with anhidrosis (P = .145), whereas a higher median age was a consistent finding in both males and females with anhidrosis. Data analyses are represented in Table I.Table IResults of statistical analyses demonstrating statistical significance regarding age of symptom onset and sex between normal and abnormal TST groups and insignificant correlation between sweat test results and menopausal statusPatient demographicsAbnormal TST (N = 25)Normal TST (N = 11)P valueAge of symptom onset (y).024Median age overall (Q1, Q3)42 (35, 60)31 (19, 43) Median age for females (Q1, Q3)42 (36, 53)27 (19, 31) Median age for males (Q1, Q3)60 (42, 69)51 (19, 51)Sex.040 Female, n (%)22 (88.0)6 (54.5) Male, n (%)3 (12.0)5 (45.5)Menopausal status (females only).145 Premenopausal, n (%)11 (50.0)5 (83.3) Postmenopausal, n (%)9 (40.9)0 (0.0) Unknown, n (%)2 (9.1)1 (16.7)Bolded P values indicate statistical significance at the 5% level (P < .05).Q, Quartile; TST, thermoregulatory sweat test. Open table in a new tab Bolded P values indicate statistical significance at the 5% level (P < .05). Q, Quartile; TST, thermoregulatory sweat test. Anhidrosis was present in 25 of 36 (69%) of consecutive patients presenting with facial flushing. TST is useful in the diagnosis of unexplained facial flushing and direct management toward educating patients to pursue lifestyle modifications such as avoiding prolonged heat exposure to reduce symptoms. These novel results suggest a mechanism for facial flushing that is not tested for during the standard facial flushing workup, and as such, a practice recommendation includes incorporation of TST in the evaluation of unexplained facial flushing, especially in older adults and female patients. None disclosed.