Objective: To define differences in digital vascular responses to cooling and to determine their usefulness for the differential diagnosis of 4 groups of subjects: patients with primary Raynaud's phenomenon (RP) (n = 96), patients with RP associated with scleroderma (systemic sclerosis, SSc) spectrum disorders (SSc spectrum RP) (n = 108), subjects complaining of cold sensitivity of the fingers (n = 88), and RP negative controls (n = 120).
Methods: Digital systolic blood pressure, digital blood flow, and digital skin temperature were measured in a temperature controlled room at 18 or 23 degrees C; the effect of local finger cooling was tested at 30, 20, 15, and 10 degrees C.
Results: Digital blood pressure responses clearly differentiate the 4 diagnostic groups from each other. By contrast, blood flow and skin temperature measurements, although showing different group means, fail to reach statistical significance due to a large variance. Digital pressure responses have high sensitivity and specificity for distinguishing not only between patients with RP and controls, but also between the 2 types of RP. A relative digital systolic pressure (digital systolic pressure over brachial systolic pressure) of less than 70% at low local finger cooling temperatures (15 and 10 degrees C) has a sensitivity of 97.1% in differentiating SSc spectrum RP from primary RP. A zero reopening pressure shows a specificity of 100% at 30 degrees C and 81.7% at 20 degrees C to separate the 2 groups. The zero reopening pressure is seldom associated with clinically visible RP (10.3% among SSc spectrum RP, 4.3% among primary RP). Although the study was not designed to investigate drug effects, our data from patients who failed to abstain from vasodilators, as instructed, show they have a protective effect at 15 and 10 degrees C.
Conclusion: The digital pressure response to cooling is a useful test for RP and cold sensitive subjects. It has high sensitivity and specificity to differentiate between SSc spectrum RP and primary RP and between primary RP and cold sensitive subjects. Our preliminary data on vasodilator use suggest that the digital pressure response to cooling may also be useful in RP treatment studies.