Forearm porphyrin levels evaluated by digital imaging system are increased in patients with systemic sclerosis compared with patients in pre-clinical stage.

We hypothesized that changes in skin characteristics on the forearm could be useful for early diagnosis of systemic sclerosis (SSc). We used VISIA digital imaging system to investigate this possibility for the first time. Twenty-eight Japanese patients who were diagnosed with typical or very early diagnosis of SSc (VEDOSS) were enrolled in this study, and ten age- and gender-matched patients with other disorders were included as a control group. Eight skin characteristics were analyzed. Our method of evaluating forearm skin characteristics was shown to be reproducible. The scores of WRINKLES, TEXTURE, PORES, and PORPHYRINS were higher in SSc subjects with sclerotic forearm skin (SSc forearm+; 11.004, 5.116, 3.230, and 0.084, respectively) and those without (SSc forearm-: 11.915, 4.898, 2.624, 0.0616, respectively) than in the non-SSc control subjects (10.075, 4.496, 2.459, 0.0223, respectively). Also, the scores of SPOTS, TEXTURE, PORES, UV SPOTS, BROWN SPOTS, and PORPHYRINS were elevated in SSc forearm+ (3.182, 5.116, 3.230, 5.761, 6.704, 0.084, respectively) and SSc forearm- patients (2.391, 4.898, 2.624, 9.835, 5.798, 0.0616, respectively) compared with those with VEDOSS (2.362, 4.738, 2.234, 5.999, 4.898, 0.0169, respectively). We found statistical significance in the difference in score of PORPHYRINS between SSc forearm- and VEDOSS groups (p = 0.044), and between SSc forearm+ and VEDOSS groups (p = 0.012). Therefore, they can be used to differentiate VEDOSS from early or mild SSc cases, which is sometimes clinically problematic. Our study also suggests that the porphyrin research will lead to a better understanding of SSc pathogenesis.