To determine if some patients who tested positive for anti-Scl-70 antibody in clinical practice, but did not have classifiable systemic sclerosis, were negative for anti-Scl-70 antibody by the more specific immunodiffusion method of testing.
Patients evaluated by a rheumatologist at a Scleroderma referral center who had tested positive for anti-Scl-70 antibody prior to referral, but did not have classifiable SSc based on clinical criteria, were invited to undergo testing for anti-Scl-70 antibody by immunodiffusion. Patient demographics and clinical features were recorded at the time of their evaluation, and diagnostic testing results were reviewed using the medical records.
52 patients were enrolled over an 8-year period, with 48 (92.3%) testing negative and 4 (7.7%) testing positive for anti-Scl-70 antibody by immunodiffusion. Of the 48 patients who tested negative, 18 (37.5%) tested negative for ANA by indirect immunofluorescence, 33 (68.8%) did not have Raynaud\'s phenomenon, and 43 (89.6%) had ≤1 clinical criteria items based on the 2013 ACR/EULAR SSc classification criteria. Nevertheless, 21 (43.8%) patients who were negative for anti-Scl-70 antibody by immunodiffusion had undergone a chest CT and 14 (29.2%) had undergone an echocardiogram. A total of 23 patients had at least one follow up clinic visit. 3 out of 4 patients who were positive for anti-Scl-70 antibody by immunodiffusion, but none of the 19 patients who tested negative by immunodiffusion, developed sufficient criteria during follow up to be classified as SSc.
Assays for anti-Scl-70 antibody in commercial laboratories that are commonly utilized in clinical practice can produce false positive results. These results can lead to angst for patients, as well as unnecessary referrals and diagnostic evaluations.

New strategies for early diagnosis and careful follow-up of systemic sclerosis are urgently needed. We unconventionally used a video capillaroscopy system to measure the amount of sweating on finger pads, and investigated its clinical significance. Thirty-three Japanese patients who were diagnosed with typical or pre-clinical stage patients of systemic sclerosis were included in this study. Five healthy subjects were also included. Among twenty-one patients with typical systemic sclerosis that fulfilled ACR/EULAR 2013 classification criteria, seven had increased sweating levels. On the other hand, among twelve pre-clinical stage patients that did not fulfill the classification criteria, no patient showed increase in finger sweating. We found that there was statistically significant difference. The ratio of diffuse cutaneous systemic sclerosis was also found to be significantly higher in subjects with increased amounts of sweating than in subjects with normal levels. Furthermore, the positivity of topoisomerase I antibody was statistically higher in patients with increased sweating levels than in those without. These results indicated that measurement of finger sweating levels may be a useful tool for early diagnosis and clarification of pathogenesis in this disease.