Two hundred and fifty-seven patients underwent thermographic assessment of RP symptoms between 2010 and 2012. The case note review identified 128 patients who fulfilled our criteria for either primary RP (n = 85) or FMS (n = 43). NC had been undertaken in 66 patients (48 primary RP). There was a greater number of current smokers in the FMS group (37.2 vs. 16.5 %, p = 0.009) but no other statistically significant differences between groups in terms of baseline demographics, conventional cardiovascular risk factors or vasodilator use (Table 1). No differences were identified between primary FMS and primary RP for either individual reported digital colour changes, the number of digital colour changes (i.e. mono-phasic, bi-phasic, etc.) or other symptom characteristics (Table 1). For each group, “white” was the most commonly reported digital colour change (~68 %) with similar proportions of patients (~30 %) reporting mono-phasic, bi-phasic and tri-phasic RP attacks.
In contrast, significantly lower skin temperature of the digits [29.0 (7.3) vs. 32.1 °C (7.3), p = 0.004], dorsum [30.2 (4.4) vs. 31.9 °C (4.3), p = 0.005] and thermal gradient [−0.9 (3.1) vs. +0.0 °C (3.0), p = 0.03] was identified in primary RP compared with FMS. Following CST, patients with primary RP continued to have significantly lower skin temperature at the digits and dorsum of the hand, with a strong trend for a lower TG post-CST compared with FMS (Table 1).
The majority of patients with both primary RP and FMS had normal NC (64.6 and 83.3 %, respectively). Subtle NC changes were found in primary RP more commonly than in FMS although this trend did not achieve statistical significance (31.3 vs. 16.7 %, p = 0.24). Due to the blinded nature of our NC review, two patients with primary RP (4.1 %) were identified in this study as having “early” scleroderma NC changes. Both patients were ANA negative and did not have any clinical features of SSc (or alternative CTD). Repeat statistical analysis excluding these two subjects from the primary RP group did not influence the outcome of the study (data not reported). There were no significant differences in skin temperature of the digits, dorsum or thermal gradient in patients with primary RP with normal NC versus abnormal NC changes (p > 0.05 for all comparisons). In contrast, FMS patients with subtle NC changes compared with those with normal NC appearances appeared to have slightly lower skin temperature of the digits (26.0 vs. 32.8 °C, p = 0.09) and a significantly lower thermal gradient (−2.4 vs. +0.5 °C, p = 0.006) although these findings must be considered with caution in the context of a low number of patients with FMS and NC changes (n = 3).
We examined the possible relationship between individuals reported digital colour changes and thermographic assessment. Across the whole cohort, reporting “blue” digital colour changes was associated with a significantly lower baseline digital (27.8 vs. 31.7 °C, p = 0.005) and baseline dorsal (29.7 vs. 31.4 °C, p = 0.007) skin temperature, along with a corresponding lower TG (−1.8 vs. −0.2 °C, p = 0.06). Significant associations were also identified in patients reporting “purple” colour changes (Table 2). When assessing the primary RP group in isolation, significantly lower baseline skin temperature was identified in patients reporting “blue” digital colour changes for the digits (27.4 vs. 30.5 °C, p = 0.017) and dorsum (29.5 vs. 31.1 °C, p = 0.023) of the hands (Table 2). Similar associations between “blue” and “purple” reported digital colour changes and skin temperature (of the digits and dorsum) were identified following cold challenge (data not reported). In contrast, there was no association between reported digital colour changes and thermographic assessment of the hands at baseline (or following cold challenge) in patients with FMS (Table 2).
Exploring the relationship between the number of colour changes in RP attacks and thermographic assessment identified some intriguing observations. Bi- and tri-phasic RP was associated with lower baseline digital and dorsum skin temperature compared with mono-phasic RP (Table 3). Digital and dorsal skin temperatures remained significantly lower in tri-phasic compared with mono-phasic RP following cold challenge in primary RP. In contrast, bi- and tri-phasic RP was associated with higher baseline skin temperature compared with mono-phasic RP in FMS (Table 3). No significant associations between the number of colour changes reported and thermographic assessment following cold challenge were identified in FMS.