The autoantibodies positive rates in SSc patients
Eighty-six patients with SSc were enrolled in this study, including 46 patients with limited SSc, 33 patients with diffuse SSc, and 7 patients with overlap syndrome. We assessed the incidence of four antibodies implicated in SSc: anti-SCL-70, anti-centromere, anti-SSA, and anti-SSB (Table 1). In our study population, 44.2% SSc patients (38/86 patients) were anti-SCL-70 antibody positive, including limited (18/38 patients, 47%) and diffuse (19/38 patients, 50%) SSc. Patients positive for anti-centromere antibody (19/86 patients, 22.1%) presented primarily with limited SSc (15/19 patients, 79%). 32.6% SSc patients (28/86 patients) were anti-SSA antibody positive, including limited (14/27 patients, 52%) and diffuse (11/28 patients, 40%) SSc, and 3 overlap syndrome patients. Only 8 SSc patients (9.3%) were anti-SSB antibody positive (Table 1). In our patient population, 1 patient was positive for both anti-SCL-70 and anti-centromere antibody, 17 patients were positive for both anti-SCL-70 and anti-SSA antibody, and 7 patients were positive for both anti-SCL-70 and anti-SSB antibody (data not shown).
Next, we assessed the incidence of the four antibodies according to disease classification (Table 2). We found that only anti-centromere antibody was significantly different between limited (32.6% positive) and diffuse (6.45% positive) SSc disease classifications (p=0.0052). Anti-SCL-70, and anti-SSB antibodies were more prevalent in diffuse than limited disease states, but the differences were not statistically significant.
The clinical phenotype and internal organ involvement of SSc patients
Forty-three SSc patients (50.0%) had lung involvement, manifested as PIF, and 44 SSc patients (51.1%) had impaired lung function, manifested as decreased DLco (Table 3). In contrast, few patients (15/86 patients, 17.4%) had PH detected by cardiac ultrasound. Raynaud's phenomenon was present in 81.4% of SSc patients (70/86 patients) as the first manifestation of SSc. The average incidence of Raynaud's phenomenon occurred approximately 49.9 months before the patient was diagnosed with SSc. The other 16 SSc patients presented with skin swelling and hardening as the first manifestations. Finally, 34 SSc patients (39.5%) had digital ulcers (Table 3).
Correlation between autoantibodies, digital ulcers, and pulmonary interstitial fibrosis
Our results showed that 68.4% SSc patients that were anti-SCL-70 antibody positive had PIF (26/38 patients), which was significantly more than SSc patients that were anti-SCL-70 antibody negative had (17/48 patients, 35.4%, p=0.0045) (Table 4). SSc patients that were anti-centromere antibody positive had less PIF (3/16 patients, 15.8%) than SSc patients that were anti-centromere antibody negative (40/67 patients, 59.8%, p=0.0013) (Table 4). SSc patients that were anti-SSA antibody positive with PIF (20/28 patients, 71.4%) had a higher incidence than SSc patients that were anti-SSA antibody negative (23/58 patients, 39.7%, p=0.0107) (Table 4). The presence of anti-SSB antibody (7/8 patients) did not associate with PIF (p=1.0000) (Table 4). Interestingly, 94.1% SSc patients with double positive for anti-SCL-70 and anti-SSA antibodies (16/17 patients) had PIF, which was a significantly higher incidence rate than anti-SCL-70 antibody single positive patients (p=0.0452) (Table 5). Digital ulcers were significantly prone to develop PIF (25/34 patients, 73.5%, p=0.0008), whereas those without digital ulcers tended to less develop PIF (Table 4). Our data did not find a significant correlation between PIF and PH (p=1.0000) (Table 4).