Abstract
Background/Objectives:
The subset of ANA-positive patients with systemic sclerosis (SSc) who lack prototypic SSc-specific autoantibodies (centromere, topoisomerase, RNA polymerase III, “triple negative SSc”) is poorly characterized. We assessed clinical features and prevalence of additional autoantibodies in these patients.
Methods:
In this case series patients with ANA+ and triple negative SSc antibodies were identified from two independent SSc cohorts (n=280) and demographic and clinical data were obtained over two years. Sera were screened for ANA and autoantibodies were examined by immunoblots. Significance was assessed through Fisher’s exact test and Student’s T-test.
Results:
Forty ANA+ triple negative SSc patients (14% of the two SSc cohorts) were identified. Mean age was 53 ± 14.5 years, 53% had limited disease, average disease duration was 9 ± 9.7 years, and MRSS was 7.6 ± 6.8. 47.5% of the patients had digital ulcers, 60% had interstitial lung disease and 15% had pulmonary hypertension. The most common immunofluorescence patterns were speckled and mixed speckled/nucleolar. Of 29 autoantibodies tested, the most prevalent were Ro-52 (50%), Th/To (40%), MDA5 (35%), SAE1 (28%). Ro-52 was associated with ILD (RR 2.67, p<0.001) and elevated CK (RR 2.64, p<0.05), and PM-75 was associated with digital ulcers (RR 2.18, p<0.05).
Conclusions:
ANA+ triple negative SSc patients represent an understudied and heterogeneous population of patients with a high prevalence of Ro-52 antibodies, an enrichment for myositis specific antibodies, and increased risk of interstitial lung disease. These patients are seen relatively frequently and should be regularly assessed for evidence of myopathy and lung involvement.
Keywords: Systemic Sclerosis, Scleroderma, Autoantibodies, Autoimmune disease
Introduction
Systemic sclerosis (SSc) is a fibrotic disease which is clinically, immunologically, and molecularly heterogeneous [1]. Ninety-five percent of patients have anti-nuclear antibodies (ANA) and most have prototypic SSc-associated antibodies including anticentromere (ACA), anti-Scl-70 (ATA), or anti-RNA polymerase-III (RNAP3), each which has strong clinical associations and are predictive of outcomes [2]. Additional SSc related antibodies including Fibrillarin and Th/To been identified but are not routinely tested. There is a subset of SSc patients in which ANA is positive, but all three prototypical SSc autoantibodies are negative (“triple negative SSc”) which represents a poorly characterized clinical population.
The purpose of this study was to identify ANA positive and triple negative SSc patients and assess their demographic and clinical characteristics. In addition, we sought to investigate the presence of other autoantibodies in this subgroup and determine clinical associations.
Materials and Methods
Study Population
Patients from University of Rochester Medical Center (URMC) and Northwestern University (NU) scleroderma repositories were evaluated. The institutional review board of the University of Rochester Medical Center (URMC) approved this case series (RSRB# 71768). This research was in compliance with the Helsinki Declaration. All participants gave written informed consent to participate. Inclusion criteria included age greater than or equal to 18 and fulfilment of the ACR/EULAR SSc diagnostic criteria [3]. Northwestern University (NU) patients also fulfilled these criteria and were drawn from a prior study [4].
Clinical Characteristics
Demographic information and clinical data were obtained from chart review and recorded from time of first SSc clinic appointment at which point blood was drawn for autoantibody testing. Patients were characterized by disease subset and modified Rodnan skin (MRSS) score at initial SSc visit. Presence of digital ulcers, telangiectasias, interstitial lung disease (ILD) on chest CT (honeycombing, ground glass opacities) were evaluated, with positivity documented at any point in time since initial visit. Pulmonary arterial hypertension (PAH) was assessed by right heart catheterization and maximum pressures were recorded. Maximum CK scores were documented.
Immunofluorescence and Immunoblot
Sera were screened for ANA by indirect immunofluorescence (IIF) on HEp-20–10 slides and fluorescence intensity, pattern, and titer were evaluated by the EUROPattern microscope and software [5]. Autoantibody confirmation was performed using immunoblots (EUROLINE SSc Profile 12 Ag (IgG); Autoimmune Inflammatory Myopathies 16 Ag et cN-1A; SSc Profile (Nucleoli), EUROIMMUIN) [5].
Positive and negative controls were used to identify the intensity of each reactivity with antibody results reported as: 0 (negative), + (borderline positivity), ++ (positive), +++ (strongly positive). No differences were noted between borderline and positive results on data stratification thus both were included.
Statistical Analysis
Demographic and clinical parameters were expressed as mean ± S.D. while categorical results were expressed as frequencies. Clinical associations between antibodies and phenotype were assessed using Fisher’s exact test. Clinical associations between number of positive antibodies and phenotype were assessed using Student’s T-test. For each test p-values < 0.05 were considered statistically significant.
Results
Patient Characteristics
Using standard clinical lab testing, fifty-seven (20.4%) patients were identified as ANA positive triple negative SSc, including 45/200 (22.5%) patients from the NU cohort and 12/80 (15%) patients from the URMC cohort. Study population characteristics are summarized in Table 1.
Table 1.
Clinical characteristics of cohort. Table depicts frequencies (percentages), or mean ± SD.
| Variables | NU (n=30) Frequency (%) |
URMC (n=10) Frequency (%) |
Combined (n=40) Frequency (%) |
|---|---|---|---|
| Demographics | |||
| Female | 25 (83.33%) | 8 (80) | 33 (82.5) |
| Age, ± mean SD years | 47 ± 10.81 | 69 ± 11.39 | 53 ± 14.49 |
| Caucasian | 20 (66.67) | 10 (100) | 30 (75) |
| Hispanic | 5 (16.67) | 0 (0) | 5 (12.5) |
| African American | 4 (13.33) | 0 (0) | 4 (10) |
| Asian/Pacific Islander | 1 (3.33) | 0 (0) | 1 (2.5) |
| ANA Pattern | |||
| Centromere | 0 (0) | 0 (0) | 0 (0) |
| Cytoplasmic | 6 (20) | 2 (20) | 8 (20) |
| Homogenous | 3 (10) | 0 (0) | 3 (7.5) |
| Nucleolar | 12 (40) | 7 (70) | 19 (47.5) |
| Partly nucleolar | 1 (3.33) | 0 (0) | 1 (2.5) |
| Speckled | 26 (86.67) | 9 (90) | 35 (87.5) |
| Subtypes | |||
| Limited Cutaneous (lcSSc) | 14 (46.67) | 7 (70) | 21 (52.5) |
| Diffuse Cutaneous (dcSSc) | 14 (46.67) | 1 (10) | 15 (37.5) |
| Overlap | 1 (3.33) | 1 (10) | 2 (5) |
| SSc Sine Scleroderma | 2 (6.67) | 1 (10) | 3 (7.5) |
| Disease Characteristics | |||
| Avg disease duration ± SD | 6 ± 5.67 | 18.8 ± 13.14 | 9 ± 9.73 |
| Telangiectasias | 22 (73.33) | 7 (70) | 29 (72.5) |
| Digital ulcers | 16 (53.33) | 3 (30) | 19 (47.5) |
| Avg MRSS ± SD | 8.13 ± 7.35 | 6 ± 4.85 | 7.55 ± 6.83 |
| ILD | 20 (66.67) | 4 (40) | 24 (60) |
| PAH | 5 (16.67) | 1 (10) | 6 (15) |
| Avg FVC ± SD (Range) | 74 ± 16.92 (21–102) | 97 ± 24.44 (50–129) | 79 ± 20.55 (21–129) |
| Avg DLCO ± SD (Range) | 61 ± 18.37 (19–89) | 63 ± 24.67 (21–102) | 62 ± 19.53 (19–102) |
| Avg CK ± SD (Range) | 159.44 ± 164.49 (31–871) | 129 ± 162.17 (31–524) | 152.54 ± 162.08 (31–871) |
NU: Northwestern University; URMC: University of Rochester Medical Center; ANA: anti-nuclear antibodies; MRSS: modified Rodnan skin score; CK: creatine kinase; ILD: interstitial lung disease; PAH: pulmonary arterial hypertension; FVC: forced vital capacity; DLCO: diffusing capacity for carbon monoxide.
Of the 57 triple negative SSc patients initially identified, 40 were confirmed by immunoblot. Of these, 33 were women (82.5%) and patients were primarily Caucasian (75.0%), with a mean age of 53.0 ± 14.5 years. Patients had a similar distribution of limited and diffuse cutaneous disease (52.5% vs 37.5%) with an average MRSS of 7.6 ± 6.8. Telangiectasia (72.5%) and digital ulcers (47.5%) were highly prevalent. The majority of patients (60.0%) had interstitial lung disease (ILD) and 15% had pulmonary artery hypertension (PAH). Average forced vital capacity (FVC) was 79.0 ± 20.6 percent predicted and diffusing capacity of lungs for carbon monoxide (DLCO) was 62.0 ± 19.5 percent predicted. Fourteen (35%) patients had elevated CK with an average CK level of 152.5 ± 162.1 U/L. No patients developed renal crisis.
Antibody Prevalence
ANA was confirmed by IIF in all patients with a mixed speckled/nucleolar (42.5%) and speckled (30.0%) patterns being most prevalent. Table 2A depicts the 29 antibodies assessed by immunoblot and categorization of prototypic scleroderma antibodies (ACA, ATA, RNAP3), scleroderma associated antibodies (SAA), and myositis antibodies (MAA) defined by the EUROIMMUN [5]. Supplemental Diagram 1 depicts the study population flow diagram and exclusion of the 17 prototypic autoantibodies. Antibody prevalence as measured by immunoblot are described in Table 2B and Supplemental Table 2. The most prevalent antibody detected was Ro-52 (50%). Ro-52 positivity was significantly associated with prevalence of ILD (RR 2.67, p = 0.0007) and elevated CK (RR 2.64, p = 0.04). Among the SAA group, Th/To (40%) and fibrillarin (25%) were the most prevalent followed by NOR-90, RNP-A, and RNP-C (7.5% each), but none were associated with specific clinical manifestations. The most common myositis associated antibodies (MAA) were MDA5 (35%) and SAE1 (27.5%). Mi-2b (20%) and PM-75 (25%) were less common, but were significantly associated with MRSS >12 (Mi-2b RR 4.00, p = 0.04) and digital ulcers (PM-75 RR 2.18, p = 0.03). Antibody associations with clinical outcomes are detailed in Table 3 and Supplemental Table 3.
Table 2.
A. Description of EUROIMMUN immunoblot antibody panels assessing twenty-nine autoantibodies assessed in the triple negative cohort (n=40). Prototypic scleroderma antibodies: Scl-70, CEN-A, CEN-B, RP11, RP155. Scleroderma associated antibodies: Th/To, Fibrillarin, NOR-90, RNP-A, RNP-C, RNP-70. Other antibodies included: PDGFR, Ro-52. Myositis Antibodies: MDA5, SAE1, Mi-2b, PM75, PM100, Ku, SRP, CN-1a, NXP2, PL-7, Jo1, Mi-2a, PL-12, T1F1g, OJ, EJ. B. Antibody prevalence by immunoblot. Antibodies with a prevalence <20% are not shown (n=20), with exception of PM75/PM100 which individually had a prevalence >20% but are listed together as the antibodies are clinically meaningful when double positive.
| A. | |
|---|---|
|
| |
| Scleroderma Panel | Scl-70, CEN-A, CEN-B, RP11, RP155, Th/To, Fibrillarin, NOR-90, RNP-A, RNP-C, RNP-70, PDGFR, Ro-52 |
|
| |
| Myositis Panel | MDA5, SAE1, Mi-2b, PM75, PM100, Ku, SRP, CN-1a, NXP2, PL-7, Jo1, Mi-2a, PL-12, T1F1g, OJ, EJ |
|
| |
| B. | |
| Antibody |
Prevalence n (%) |
|
| |
| Ro-52 | 20 (50) |
| Th/To | 16 (40) |
| MDA5 | 14 (35) |
| SAE1 | 11 (27.5) |
| Fibrillarin | 10 (25) |
| Ku | 9 (22.5) |
| Mi-2b | 8 (20) |
| PM75 / PM100 | 6 (15) |
Table 3.
Assessment of autoantibodies and associated significant clinical outcomes. For each clinical outcome [interstitial lung disease (ILD), modified Rodnan skin score (MRSS), creatine kinase (CK), and digital ulcers] patients were stratified by autoantibody and associations were determined using a Fisher’s exact test. Prevalence of each clinical feature was calculated based on antibody prevalence. Statistically significant results (p<0.05) are bolded.
| Antibody | ILD | MRSS >12 | CK (>145) | Digital ulcers | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| n (%) | RR (95% CI) | p-value | n (%) | RR (95% CI) | p-value | n (%) | RR (95% CI) | p-value | n (%) | RR (95% CI) | p-value | |
|
| ||||||||||||
| Ro-52 | 17 (85) | 2.67 (1.51 – 5.29) | 0.0007 | 4 (20) | 1 (0.30 – 3.25) | >0.99 | 10 (50) | 2.64 (1.11 – 6.96) | 0.04 | 11 (55) | 1.37 (0.71 – 2.74) | 0.53 |
| PM75 | 6 (60) | 1.10 (0.54 – 1.84) | >0.99 | 2 (20) | 1.00 (0.25 – 3.50) | >0.99 | 4 (40) | 1.00 (0.38 – 2.22) | >0.99 | 8 (80) | 2.18 (1.17 – 3.85) | 0.03 |
| Mi-2b | 5 (63) | 1.12 (0.52 – 1.85) | >0.99 | 4 (50) | 4.00 (1.25 – 11.75) | 0.04 | 2 (25) | 0.67 (0.18 – 1.78) | 0.68 | 5 (63) | 1.43 (0.65 – 2.56) | 0.44 |
Many patients were positive for multiple autoantibodies (mean 3.68 ± SD 2.3), and this was associated with increased severity of PFT parameters. A Student’s T test was used to assess clinical significance. Patients with ≥3 antibodies (n=30) had lower FVC scores compared to patients with 0–2 antibodies (n=10, p=0.005) and lower DLCO scores (p=0.02) (Supplemental Table 4).
Discussion
In this study we sought to better characterize SSc patients with ANA positivity who were negative for the prototypic SSc autoantibodies (centromere, topoisomerase, and RNA polymerase III). We identified 40 patients who met these parameters and were able to detect autoantibodies in the vast majority of these patients by immunoblot. Patients had a high prevalence of ILD and MSA (myositis specific antibodies)/MAA,[6] and importantly some antibodies were associated with specific clinical manifestations. Additionally, patients with increased numbers of autoantibodies (≥3) were associated with more severe interstitial lung disease.
Most SSc case series extensively characterize patients with Scl-70, centromere, and RNA polymerase III antibodies, but lack description of patients who are negative for these. Patients in this study were included based on the ACR/EULAR criteria, which only accounts for the prototypic SSc antibodies. For future diagnostic purposes, inclusion of any SSc-specific antibody (not limited to the three prototypic antibodies) may allow for a more inclusive SSc definition and should be considered.
Only three studies primarily focused on ANA negative patients reported on the ANA positive triple negative SSc group [7–9]. Miyake et al. identified 5.3% of patients were ANA positive triple negative SSc with median MRSS of 13, ILD in 62%, and pulmonary hypertension in 3% [7]. Hudson et al found only 1.8% of 874 patients to be ANA positive but ENA negative, and reported a lower prevalence of ILD (12.5%) [8]. Liu et al. identified that telomere length was shorter in triple negative SSc patients in comparison to patients with prototypic antibodies, and this was associated with ILD and increased risk for deterioration in lung function [9]. Compared to these studies from Japan and Canada, the prevalence of SSc patients who were ANA positive triple negative was significantly higher in our combined US cohort at 14%. While we observed a higher prevalence of these patients, we found similar clinical features with 60% of patients with ILD and mild skin involvement (MRSS 7.55).
Of the 29 antibodies tested by immunoblot, patients in our two cohorts showed positivity for 26, with the highest prevalence seen for Ro-52, Th/To, and MDA5. Routine clinical autoantibody testing failed to detect patients with weakly positive SSc-associated antibodies and 17 patients (6%) were initially classified as triple negative SSc based on routine clinical testing. These patients were re-classified as positive for one the prototypic antibodies after immunoblot which has improved sensitivity. The distinction between clinical and immunoblot testing shows that the definition of ‘triple negative SSc’ patients is dependent upon the testing used.
Anti-Ro52 (TRIM21) was the most prevalent antibody in our triple negative SSc patients (50%). Hudson et al. previously reported Ro-52 antibodies in 20% of a large cohort of SSc patients, which were associated with ILD and overlap syndrome including 11.5% of patients with Ro-52 demonstrating inflammatory myositis [10]. Our study confirmed these findings with Ro-52 being associated with increased risk of ILD and elevated CK.
While not a myositis-specific antibody, Ro-52 is highly prevalent in myositis patients and frequently co-occurs with anti-synthetase antibodies [11]. Moreover, the co-existence of SSc and myositis/myopathy identifies patients with poor prognosis [12], so we investigated patient sera for a variety of MSA/MAA. Multiple MSA/MAA (n=15) were observed in the triple negative SSc cohort and classified as described in Leurs et al. [6]. We found the prevalence of MSA at 32.5% and MAA at 30%. These proportions are elevated in the triple negative SSc patients compared to the literature, where 8% had MSA and 9.7% had MAA in a European SSc cohort. No patients with myositis antibodies also fulfilled the EULAR/ACR inflammatory myopathy classification criteria, suggesting that myositis patients were not misclassified as having SSc. We also found high proportion of patients positive for anti-MDA5 antibodies compared to previous reports [6]. Because the majority of the MDA5 titers were low and these patients did not demonstrate classic MDA5 clinical presentations such as rapidly progressive ILD or digital ulcerations [13], further testing should be performed to confirm these positive results. Among the less prevalent MSA/MAAs, we also found an association between Mi-2b and elevated MRSS and an association between PM-75 antibodies and digital ulcers. Mi-2b is frequently identified in dermatomyositis but there is a paucity of data on clinical correlates of this autoantibody in SSc. Wodkowski et al. described associations between PM-75 and calcinosis but not ulceration [14].
This study was limited in its power to detect associations between individual autoantibodies and clinical manifestations due to the relatively low prevalence of triple negative SSc patients and each of the specific antibodies. Further studies are needed to confirm our results in larger populations and to assess additional clinical parameters such as nailfold capillaroscopy. The autoantibodies assessed are not exhaustive and additional valuable information could be assessed through testing for more recently described novel antibodies [15]. The sensitivity and specificity of individual assays should also be compared to gold standard assays, such as immunoprecipitation assays, as commercial autoantibody assays are not always accurate. This validation is essential when IIF shows patterns inconsistent with results obtained by commercial immunoassay, and can further characterize potential non-specific positive results. The sensitivity and specificity of the immunoblot has not been compared to other commercially available antibody tests in this population. Another limitation is that while the high prevalence of myositis antibodies is important, we only characterized CK levels as did not have standardized clinical data to indicate weakness or other objective findings of myositis.
Performing extended antibody panel testing such as the immunoblot panel used in this study is rational in patients with clinical triple negative SSc. Knowledge of specific autoantibodies (Ro-52, PM-75, Mi-2b) should make the clinician consider more diligent screening. Ro-52 (SS-A) is part of the standard ENA panel and certainly should be assessed in all SSc patients given its association with ILD. These patients should be more closely monitored with baseline chest CT and frequent PFTs. In patients with MSA/MAA, additional focus should be given to assessing potential muscle disease including a complete neurologic exam with manual muscle testing, assessment of muscle enzymes, and consideration of an EMG or MRI. Since the extended immunoblot antibody profile is not routinely available, clinicians may consider ordering a myositis antibody panel and additional SSc serologies in triple negative patients.
In conclusion, ANA positive patients who are negative for prototypic SSc antibodies have a high prevalence of Ro-52 antibodies, an enrichment for myositis specific antibodies, and increased risk of interstitial lung disease. These patients are seen relatively frequently (14% of SSc patients in this cohort) and should be regularly assessed for evidence of myopathy and lung involvement.
Supplementary Material
Acknowledgements:
The authors would like to thank EUROIMMUN US for providing the necessary test kits for the study.
Source Funding:
This work was supported by EUROIMMUN US. This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. The authors received no financial support for the research, authorship, and/or publication of this article. Each author declares that he/she has no relevant material interests that are directly or indirectly related to the work submitted for publication, with exception of the EUROIMMUN US team who are employees of EUROIMMUN US.
Footnotes
Conflicts of Interest: The authors declare that there is no conflict of interest.
References
- 1.Mehra S, Walker J, Patterson K, Fritzler MJ. Autoantibodies in systemic sclerosis. Autoimmun Rev. 2013;12(3):340–54. doi: 10.1016/j.autrev.2012.05.011. [DOI] [PubMed] [Google Scholar]
- 2.Hamaguchi Y Autoantibody profiles in systemic sclerosis: predictive value for clinical evaluation and prognosis. J Dermatol. 2010;37(1):42–53. doi: 10.1111/j.1346-8138.2009.00762.x. [DOI] [PubMed] [Google Scholar]
- 3.van den Hoogen F, Khanna D, Fransen J, Johnson SR, Baron M, Tyndall A, et al. 2013 classification criteria for systemic sclerosis: an American college of rheumatology/European league against rheumatism collaborative initiative. Ann Rheum Dis. 2013;72(11):1747–55. doi: 10.1136/annrheumdis-2013-204424. [DOI] [PubMed] [Google Scholar]
- 4.Korman BD, Marangoni RG, Hinchcliff M, Shah SJ, Carns M, Hoffmann A, et al. Brief Report: Association of Elevated Adipsin Levels With Pulmonary Arterial Hypertension in Systemic Sclerosis. Arthritis Rheumatol. 2017;69(10):2062–8. doi: 10.1002/art.40193. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 5.Liaskos C, Marou E, Simopoulou T, Barmakoudi M, Efthymiou G, Scheper T, et al. Disease-related autoantibody profile in patients with systemic sclerosis. Autoimmunity. 2017;50(7):414–21. doi: 10.1080/08916934.2017.1357699. [DOI] [PubMed] [Google Scholar]
- 6.Leurs A, Dubucquoi S, Machuron F, Balden M, Renaud F, Rogeau S, et al. Extended myositis-specific and -associated antibodies profile in systemic sclerosis: A cross-sectional study. Joint Bone Spine. 2021;88(1):105048. doi: 10.1016/j.jbspin.2020.06.021. [DOI] [PubMed] [Google Scholar]
- 7.Miyake M, Matsushita T, Takehara K, Hamaguchi Y. Clinical features of Japanese systemic sclerosis (SSc) patients negative for SSc-related autoantibodies: A single-center retrospective study. Int J Rheum Dis. 2020;23(9):1219–25. doi: 10.1111/1756-185X.13908. [DOI] [PubMed] [Google Scholar]
- 8.Hudson M, Satoh M, Chan JY, Tatibouet S, Mehra S, Baron M, et al. Prevalence and clinical profiles of ‘autoantibody-negative’ systemic sclerosis subjects. Clin Exp Rheumatol. 2014;32(6 Suppl 86):S-127–32. [PubMed] [Google Scholar]
- 9.Liu S, Chung MP, Ley B, French S, Elicker BM, Fiorentino DF, et al. Peripheral blood leucocyte telomere length is associated with progression of interstitial lung disease in systemic sclerosis. Thorax. 2021. doi: 10.1136/thoraxjnl-2020-215918. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 10.Hudson M, Pope J, Mahler M, Tatibouet S, Steele R, Baron M, et al. Clinical significance of antibodies to Ro52/TRIM21 in systemic sclerosis. Arthritis Res Ther. 2012;14(2):R50. doi: 10.1186/ar3763. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11.Rutjes SA, Vree Egberts WT, Jongen P, Van Den Hoogen F, Pruijn GJ, Van Venrooij WJ. Anti-Ro52 antibodies frequently co-occur with anti-Jo-1 antibodies in sera from patients with idiopathic inflammatory myopathy. Clin Exp Immunol. 1997;109(1):32–40. doi: 10.1046/j.1365-2249.1997.4081308.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12.Paik JJ, Wigley FM, Shah AA, Corse AM, Casciola-Rosen L, Hummers LK, et al. Association of Fibrosing Myopathy in Systemic Sclerosis and Higher Mortality. Arthritis Care Res (Hoboken). 2017;69(11):1764–70. doi: 10.1002/acr.23291. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13.Moghadam-Kia S, Oddis CV, Aggarwal R. Anti-MDA5 Antibody Spectrum in Western World. Curr Rheumatol Rep. 2018;20(12):78. doi: 10.1007/s11926-018-0798-1. [DOI] [PubMed] [Google Scholar]
- 14.Wodkowski M, Hudson M, Proudman S, Walker J, Stevens W, Nikpour M, et al. Clinical correlates of monospecific anti-PM75 and anti-PM100 antibodies in a tri-nation cohort of 1574 systemic sclerosis subjects. Autoimmunity. 2015;48(8):542–51. doi: 10.3109/08916934.2015.1077231. [DOI] [PubMed] [Google Scholar]
- 15.Mecoli CA, Casciola-Rosen L. An update on autoantibodies in scleroderma. Curr Opin Rheumatol. 2018;30(6):548–53. doi: 10.1097/BOR.0000000000000550. [DOI] [PMC free article] [PubMed] [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.