Correlation between the infrared thermogram and microvascular abnormalities of the nailfold in patients with systemic sclerosis

Introduction
Systemic sclerosis (SSc) is a multisystemic disease with an extensive microvasculopathy. The gold standard for its investigation is nailfold videocapillaroscopy (NVC). Aim: To assess the value of thermography (IRT) for the assessment of microvasculopathy in patients with SSc.

Material and methods
Nineteen patients with limited cutaneous SSc were enrolled in the study. They underwent IRT imaging and NVC. An average temperature (Tavg) at the nailfold and a gradient of temperatures (∆Tavg) between the central metacarpus of the hand and the nailfold was determined for all fingers. NVC pictures were classified to capillaroscopic patterns according to Cutolo et al. system and they were analysed quantitatively to measure the density of capillaries and to calculate capillaroscopic skin ulcers risk index (CSURI) for each finger separately.

Results
There was only a moderate correlation (0.4 < r < 0.6) between thermographic parameters and density of capillaries in fingers II–V (r = 0.5; p < 0.001 for Tavg and r = –0.45; p < 0.001 for ∆Tavg), but none in thumbs (r = 0.29; p = 0.089 for Tavg and r = –0.19; p = 0.275 for ∆Tavg). Early pattern was associated with a significantly greater surface temperature (Tavg) of nailfolds and essentially milder ∆Tavg in fingers II–V when compared to all other capillaroscopic patterns in fingers II–V. Surface temperature (Tavg) was significantly lower and ∆Tavg was markedly more pronounced in fingers II–V with a greater risk of development of digital ulcers (DU) calculated by CSURI.

Conclusions
Although IRT measurements correlate only moderately with density of capillaries, this technique seems to be substantial to determine the capillaroscopic pattern and to identify patients at greater risk of DU development.