Identification of Clinical Features and Autoantibodies Associated With Calcinosis in Dermatomyositis

Importance  Prior studies have estimated that up to 20% of adults with dermatomyositis (DM) have calcinosis, which can lead to significant morbidity. Identification of risk factors may provide a better understanding of the pathogenesis and ultimately therapy for this difficult clinical problem. Risk factors for calcinosis in adults with DM have not been extensively studied.

Objectives  To determine the prevalence of calcinosis and to identify associated clinical features in a cohort of extensively phenotyped adults with DM.

Design, Setting, and Participants  A cross-sectional study of 126 patients diagnosed as having DM from January 1, 2006, through January 1, 2013, was performed. Patients were adults (≥18 years of age) attending the Stanford University Medical Center clinic.

Main Outcomes and Measures  Calcinosis, defined as the presence of calcium deposition in the skin and subcutaneous tissues on physical examination.

Results  Fourteen patients (11.1%) had calcinosis, with the extremities most commonly involved. Patients with vs those without calcinosis had a longer disease duration (median, 6.9 years; range, 2.4–18.1; vs median, 3.9 years; range, 0.2-19.2 years; P = .003) and more fingertip ulcers (50.0% vs 9.3%, P < .001). An association between calcinosis and both interstitial lung disease and anti–MDA-5 autoantibodies was identified, but this association did not persist in multivariate models that adjusted for fingertip ulcers. Fingertip ulcers and disease duration were strongly associated with calcinosis in all multivariate models, independent of the underlying autoantibody present. Autoantibodies to NXP-2 were associated with calcinosis (odds ratio, 15.52; 95% CI, 2.01-119.90), whereas anti–transcriptional intermediary factor 1-γ antibodies were protective (odds ratio, 0.2; 95% CI, 0.01-0.99) in multivariate analyses that adjusted for fingertip ulcers and other covariates.

Conclusions and Relevance  Calcinosis was a relatively uncommon clinical feature in our cohort of adults with DM. Our data suggest that calcinosis is positively associated with longer disease duration, fingertip ulcers, and NXP-2 autoantibodies and negatively associated with transcriptional intermediary factor 1-γ antibodies. A common vascular mechanism may underlie the development of both calcinosis and fingertip ulcers in patients with DM.

Dermatomyositis (DM) is a systemic autoimmune disease characterized by chronic inflammation of skin and muscles.¹ Calcinosis, which is the deposition of calcium in the skin and subcutaneous tissues, develops in 20% to 70% of patients with juvenile dermatomyositis (JDM)^2,3 and up to 20% of adults with DM.^4-6 It is often painful and may cause recurrent episodes of local inflammation or infection, leading to considerable distress and disability.⁷ Calcinosis may present as small superficial papules or nodules, deeper nodules or tumors in the dermis or subcutaneous tissue, or diffuse deposits along the myofascial planes, which, if generalized, can form an extensive exoskeleton.^7,8

Case reports and small case series have described the benefits of using various medical therapies to treat calcinosis in patients with DM, including warfarin sodium, bisphosphonates, minocycline, diltiazem, probenecid, aluminum hydroxide, sodium thiosulfate, colchicine, and intravenous immunoglobulin.⁴ Unfortunately, no medical therapy is reliably efficacious, and surgical management is often the best option.^4,9

Little is known about the pathogenesis of calcinosis in DM. One possible mechanism is the release of calcium from mitochondria in muscle cells damaged by myopathy.⁶ Macrophages, proinflammatory cytokines, and the impairment of calcium-regulating proteins have also been implicated.¹⁰ Furthermore, in patients with systemic sclerosis, digital ischemic ulcers are associated with calcinosis, suggesting a role of vascular ischemia and injury.^10-12

Between 60% and 70% of patients with DM are reported to have circulating, myositis-specific autoantibodies that are associated with particular clinical features.^13,14 Several novel autoantibody targets in DM have been recently identified. MDA-5, CADM-140, and IFIH1 are targeted in patients with mild or no muscle disease, rapidly progressive interstitial lung disease (ILD), cutaneous ulcers, and palmar papules that have vasculopathy on histopathologic analysis.¹ Antibodies against p155/140, TRIM33, and transcriptional intermediary factor 1-γ (TIF1-γ) are associated with cancer in adults (60%-80%) and low rates of ILD but more widespread and severe skin disease in JDM; NXP-2/MJ antibodies were initially described in patients with JDM who were at higher risk for calcinosis.¹⁵ Recent data suggest that antibodies against NXP-2 are also associated with cancer in adults with DM.^16,17

Previous studies^18,19 of patients with JDM have identified particular clinical features associated with calcinosis, including longer disease duration, sustained disease activity, and internal organ involvement. Although antibodies to NXP-2 have been associated with calcinosis in JDM,²⁰ there are conflicting data with regard to this association in adults with DM.^17,21,22 We sought to identify the clinical features associated with calcinosis in our cohort of extensively phenotyped adults with DM.

This is a cross-sectional study of 126 patients with DM. The study was approved by the institutional review board at Stanford University. We retrospectively collected demographic information, symptoms, physical examination findings, and internal organ involvement. All patients provided written informed consent.

We included all adults (≥18 years of age) diagnosed as having DM and followed up in the rheumatology and dermatology clinics at Stanford University Medical Center from January 1, 2006, through January 1, 2013. We excluded patients with a diagnosis of mixed connective tissue disease whose features were not primarily consistent with DM, patients with other overlap connective tissue disease, and patients with JDM. Patients were diagnosed as having DM according to the Bohan and Peter²³ criteria for DM and the modified Sontheimer²⁴ criteria for clinically amyopathic DM.

The objective of our study was to determine the prevalence of calcinosis in our cohort of patients with DM and to identify associated clinical features. Calcinosis was defined as the presence of calcium deposition in the skin and subcutaneous tissues on physical examination regardless of its extent or severity.²⁵ Radiographic confirmation was not required.

Plasma was screened for DM-specific and associated autoantibodies as previously described.^1,16,26 Briefly, antibodies against NXP-2 and MDA-5 were detected by immunoprecipitations using [35S]-methionine–labeled in vitro transcription and translation proteins. TIF1-γ antibodies were determined by an immunoprecipitation and blot assay, whereas Mi-2 and SAE1/2 antibodies were detected by immunoprecipitation using [35S]-methionine–labeled proteins generated by in vitro transcription and translation from the appropriate complementary DNAs. Jo-1 and Ro-52 antibodies were assayed by enzyme-linked immunosorbent assay.

Descriptive statistics and frequency distributions of all variables of interest were reported as proportion for categorical variables and as mean (SD) or median (range) for continuous variables. We performed univariate analysis to characterize patients with and without calcinosis with respect to demographic characteristics, clinical features, antibodies, disease duration, and measures of highest disease activity, using χ² test for categorical variables or the t test for continuous variables if a normal distribution was observed and nonparametric methods for continuous variables without a normal distribution. Logistic regression models were developed to obtain odds ratios (ORs) that related calcinosis to various variables. We selected statistically significant univariate variables to establish predictors for multivariate analysis. The logistic regression model β-coefficient was evaluated with and without potential confounders and adjusted for them if inclusion in the model changed it by greater than 10%.

Statistical significance was defined as P ≤ .05. All statistical analysis was performed using SAS statistical software, version 9.3 (SAS Institute Inc).

Of 126 adults with DM, 93 were women (73.8%), and the racial distribution was 66.4% white, 11.2% Asian, 12.8% Hispanic, 4.0% African American, and 5.6% unknown. Mean age at diagnosis was 50.0 (14.8) years, 22.2% had clinically amyopathic DM, and 83.6% had DM-specific antibodies. Fourteen patients (11.1%) developed calcinosis. Sites affected by calcinosis are listed in Table 1. Calcinosis was most common on the extremities (Figure, A) and axilla but not on the hands. In some patients, the calcinosis was deposited in large subcutaneous tumors (Figure, B).

Table 2 lists the demographic and clinical features of patients with and without calcinosis. Patients with calcinosis had longer median disease duration from DM diagnosis to last clinic visit (6.9 [2.4-18.1] vs 3.9 [0.2-19.2] years; P = .003) than patients without calcinosis. There was a trend for whites to be less likely to develop calcinosis relative to other races. More patients in the calcinosis group had interstitial lung disease (53.9% vs 15.2%, P < .001) and fingertip ulcers (50.0% vs 9.3%, P < .001) but not other types of mucocutaneous ulceration (Table 2).

Autoantibodies against MDA-5 and Ro-52 were more frequently found in patients with vs those without calcinosis (35.7% vs 9.8%, P = .006, and 42.9% vs 17.9%, P = .02, respectively). Anti–NXP-2 antibodies were also more frequently found in patients with vs those without calcinosis (28.6% vs 10.7%, P = .06). In contrast, anti–TIF1-γ antibodies were less frequently found in patients with vs those without calcinosis (14.3% vs 45.5%, P = .02) (Table 3). Of the 6 patients with calcinosis with anti–Ro-52, 2 had autoantibodies against MDA-5 and 1 had autoantibodies against TIF1-γ.

Because these autoantibodies define groups of patients with certain clinical features, we thought it likely that many of these clinical and laboratory features might not be independently associated with calcinosis because of confounding. For example, anti–MDA-5 antibodies are associated with both ILD and fingertip ulcers.¹ Because these antibodies are often mutually exclusive,¹⁴ these analyses require separate models to analyze the effect of each antibody. Thus, we examined separate multivariate models for each antibody (NXP-2, MDA-5, and TIF1-γ), while including all other significant predictors identified in Table 2. In all 3 models, fingertip ulcers and increasing duration of disease were risk factors for the presence of calcinosis (Table 4). In addition, antibodies to NXP-2 were significantly associated with calcinosis (OR, 15.52; 95% CI, 2.0-119.9; P = .009), whereas antibodies to TIF1-γ were protective of calcinosis (OR, 0.2; 95% CI, 0.01-0.99; P = .04). Interstitial lung disease was not significantly associated with calcinosis in multivariate analyses.

Interestingly, the strong association between calcinosis and anti–MDA-5 antibodies did not persist when disease duration, fingertip ulcers, and ILD were included in the model. We hypothesized that this might be due to the strong association between anti–MDA-5 antibodies and fingertip ulcers. This theory was supported by evaluation of another multivariate model that excluded fingertip ulcers, which then demonstrated that anti–MDA-5 antibodies were highly predictive of calcinosis (OR, 6.9; 95% CI, 1.8-27.0; P = .005) (data not shown).

Calcinosis is a significant clinical problem for patients with autoimmune disease, especially systemic sclerosis and DM. Traditionally, it is believed that calcinosis occurs more often in the JDM population, although data are scarce on the prevalence in adults with DM. We found a prevalence of calcinosis of 11.1% in this large cohort of adults with DM. Our data suggest that calcinosis is more frequent in patients with longer disease duration, which is consistent with prior studies²⁷ and with the view that this complication results from damage caused by longstanding disease activity.²⁸ Prior studies have used time to initiation of therapy or number of prescribed immunosuppressants as indirect measures of time of active disease. Measures of disease activity have been developed and partially validated as measures of response to therapy,²⁹ although it is unclear whether disease activity as defined by these measures is associated with calcinosis.

A novel finding in our study was that calcinosis in adults with DM was strongly associated with fingertip ulcers. Interestingly, ulcers on other areas of skin (including the oral mucosa) were not associated with calcinosis. The cause of digital ulceration in DM is currently unclear, although vascular inflammation and/or injury likely plays an important role because biopsy specimens of fingertip lesions in patients with DM demonstrate a vasculopathy.¹ Thus, vascular injury may be involved in the pathogenesis of both digital ulcers and calcinosis, which has been previously suggested in patients with systemic sclerosis.^11,12 Another explanation for this association is that, because ulcerations frequently develop in areas with calcinosis in patients with systemic sclerosis,³⁰ the same could happen in patients with DM, although in our patients, calcifications did not occur in sites of ulceration (data not shown). It is unclear why other sites of ulceration were not significantly associated with calcinosis, although all forms of ulcers tended to be associated with calcinosis, and low numbers may have precluded statistical significance.

We also evaluated whether any of the DM-specific or associated autoantibodies were risk factors for calcinosis. In our cohort, the autoantibody NXP-2 was strongly associated with calcinosis in multivariate analysis (OR, 15.52; 95% CI, 2.01-119.90; P = .009), consistent with prior studies in JDM and one study in adults with DM,³¹ and yielded a nonstatistically significant trend (P = .06) with calcinosis in the univariate analysis. Certainly, it is possible that adjusting for confounders might have strengthened the statistical association because we needed to correct for confounders to unveil the association between NXP-2 and calcinosis. In our opinion, the results of the multivariate analysis are the most robust way of looking at this association. MDA-5 antibodies were not associated with calcinosis in multivariate analyses, although they were more common in patients with calcinosis, likely because of their strong association with fingertip ulcers. Patients with the circulating autoantibody MDA-5 have a characteristic cutaneous phenotype that consists of skin ulceration and/or tender palmar papules that show vasculopathy on skin biopsy specimens.¹ They also have an increased risk of oral pain and/or ulceration, hand swelling, arthritis and arthralgia, diffuse hair loss, and ILD, associated with little or absence of myositis. Our data support the consideration of calcinosis as part of this phenotype. Interestingly, antibodies to TIF1-γ were observed with a high frequency in our overall cohort (42.1%) and were inversely associated with calcinosis (OR, 0.20; 95% CI, 0.01-0.99; P = .04). Along with other studies, we have found that DM patients with TIF1-γ antibodies tend to have a more treatment-resistant and chronic course of skin disease,^14,32 which traditionally is thought to be a risk factor for the development of calcinosis, at least in the JDM population. Consequently, our finding that this group of patients tends to have less calcinosis is somewhat surprising and suggests that our understanding of pathogenic risk factors for calcinosis is incomplete.

The current study is the first, to our knowledge, to examine specific risk factors for calcinosis in a large, well-phenotyped cohort of adults with DM. However, because this patient population is a sample from a tertiary care clinic, our results may not be generalizable. Because our study has the potential for significant confounding, we used multivariate methods to adjust for the well-defined risk factors; however, it is possible that other relevant risk factors may have been missed. Finally, the small sample size of patients who developed the outcome limited the potential to build models with more predictors; therefore, these results should be validated in other existing cohorts and future prospective studies.

Calcinosis is a relatively uncommon clinical feature in patients with DM and is associated with autoantibodies to NXP-2, whereas anti–TIF1-γ appears to be protective. Calcinosis is associated with longer disease duration and fingertip ulcers. A common underlying vascular mechanism between calcinosis in DM and digital ulcers is suggested by our data. A medication known to prevent or ameliorate vascular dysfunction in other connective tissue disorders (such as phosphodiesterase 5 inhibitors, endothelin receptor antagonists, or prostacyclins) might be effective for the prevention or treatment of calcinosis in patients with DM.

Accepted for Publication: December 12, 2013.

Corresponding Author: David Fiorentino, MD, PhD, Department of Dermatology, Stanford University School of Medicine, 450 Broadway, Pavilion C, Room 234, Stanford, CA 94063 (Fiorentino@stanford.edu).

Published Online: May 28, 2014. doi:10.1001/jamadermatol.2013.10416.

Author Contributions: Dr Valenzuela had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study concept and design: All authors.

Acquisition, analysis, or interpretation of data: All authors.

Drafting of the manuscript: Valenzuela.

Critical revision of the manuscript for important intellectual content: Chung, Casciola-Rosen, Fiorentino.

Statistical analysis: Valenzuela, Chung, Fiorentino.

Study supervision: Chung, Fiorentino.

Conflict of Interest Disclosures: None reported.