Mobile phone thermography of the toes in patients with systemic sclerosis-a pilot study

To investigate the hypotheses that in patients with SSc, the temperature gradient between the dorsum of the foot and toes (distal-dorsal difference [DDD]) is 'more negative' (toes cooler) than in healthy controls, is greatest along the first (great) toe and that the severities of thermographic abnormalities in the feet and hands are correlated.

Thermographic images of the dorsum of each hand and foot were captured using a thermal camera attached to an iPhone in 40 patients with SSc and 20 healthy controls. DDDs along the fingers (index, middle, ring and little) and toes (great toe and 'others') were measured.

There was a non-significant trend for the great toes to be colder in patients with SSc than in controls. The mean great toe DDD was more negative in patients (right: -2.89°C, left: -2.91°C, mean: -2.90°C) than in controls (right: -2.36°C, left: -2.42°C, mean: -2.39°C) (P = 0.37 for mean values). Patients' great toes were colder than 'other' (lesser) toes (right: -2.58°C, left: -2.63°C), although not significantly. In patients with SSc, finger and great toe temperature gradients were correlated (r = 0.406, ρ = 0.01).

Our findings suggest that the great toe is the coldest in patients with SSc and that patients with the coldest fingers tend to have the coldest toes. Severe RP symptoms in the hands should prompt podiatry assessment and foot care education. Mobile phone thermography is a convenient tool for assessing the digital vasculature but first requires validation in larger studies with a longitudinal component.