Overlap myositis, a distinct entity beyond primary inflammatory myositis: A retrospective analysis of a large cohort from the REMICAM registry

Myositis and Its Mimics: Guideline Updates, MRI Characteristics, and New Horizons

Myositis is defined as inflammation within skeletal muscle and is a subcategory of myopathy, which is more broadly defined as any disorder affecting skeletal muscle. Myositis may be encountered as a component of autoimmune and connective tissue diseases, where it is described as idiopathic inflammatory myopathy (IIM). Myositis can also be caused by infections as well as toxins and drugs, including newer classes of medications. MRI plays an important role in the diagnosis and evaluation of patients with suspected myositis, but many entities may have imaging features similar to those of myositis and can be considered myositis mimics. These include muscular dystrophies, denervation, deep venous thrombosis, diabetic myonecrosis, muscle injury, heterotopic ossification, and even neoplasms. In patients with suspected myositis, definitive diagnosis may require integrated analysis of imaging findings with clinical, laboratory, and pathology data. The objectives of this article are to review the fundamental features of myositis, including recent updates in terminology and consensus guidelines for IIMs; the most important MRI differential diagnostic considerations for myositis (i.e., myositis mimics); and new horizons, including the potential importance of artificial intelligence and multimodal integrated diagnostics in the evaluation of patients with muscle disorders.

Sarcoplasmic Myxovirus Resistance Protein A: A Study of Expression in Idiopathic Inflammatory Myopathy

Background

Idiopathic inflammatory myopathies (IIM) are a heterogeneous group of autoimmune diseases affecting primarily proximal muscles. Major subtypes include dermatomyositis, polymyositis, inclusion body myositis, immune-mediated necrotizing myopathy and antisynthetase syndrome. Overexpression of sarcoplasmic myxovirus-resistance protein A (MxA) has been observed in muscle biopsy specimens of dermatomyositis but is rarely seen in other subtypes of IIM and other myopathies.

Objective

We evaluate the expression of sarcoplasmic MxA and its diagnostic value in IIM and other myopathies.

Methods

One hundred and thirty-eight muscle biopsy specimens with the diagnosis of IIM and other myopathies from 2011 to 2020 were reviewed and stained for MxA by immunohistochemistry. The difference of the expression of MxA between IIM and other myopathies was analyzed by Fisher's exact test, and the sensitivity and specificity of MxA immunohistochemistry in the diagnosis of IIM were assessed.

Results

MxA protein was positive in 16/138 (11.6%) specimens. All 12 dermatomyositis specimens positive for MxA protein were positive in perifascicular area pattern. Only dermatomyositis specimens had a significantly higher percentage of positive sarcoplasmic MxA expression than specimens of other subtypes of IIM (p<0.001). Sarcoplasmic MxA expression for dermatomyositis diagnosis had a sensitivity of 46.15% (95% CI 26.59-66.63%) and a specificity of 94.44% (95% CI 81.34-99.32%) with the positive and negative likelihood ratio of 8.31 (95% CI 2.03-34.01) and 0.57 (95% CI 0.40-0.82), respectively.

Conclusion

The MxA immunohistochemistry is highly specific for dermatomyositis and should be added to a routine inflammatory panel of muscle biopsy. MxA expression should be cautiously interpreted to avoid pitfalls.

What should we expect when two myositis-specific antibodies coexist in a patient

BACKGROUND

The coexistence of two myositis-specific autoantibodies (MSA) is considered extremely rare. We describe three patients with both anti-signal recognition particle (SRP) antibodies and another MSA in serum.

METHODS

We performed a retrospective clinical data collection and follow-up studies of the clinical manifestations and treatment outcome of three patients positive with anti-SRP antibodies and other MSAs. IgG antibodies against MSAs were detected using commercial line immunoblot assay.

RESULTS

The tests of MSA showed positive result of anti-SRP antibodies and another one MSA including anti-TIF1-γ, anti-Jo1, or anti-EJ antibodies, respectively. The proximal muscle weakness appeared in 2 patients; interstitial lung disease presented in 2 patients. The serum CK level was elevated in 1 patient. The muscle biopsy showed necrotizing myopathy in 1 patient and deposition of membrane attack complex on scattered myofibers in the other one patient. One of the two patients with interstitial lung disease died because of respiratory failure. One patient had completely improved and the other one showed partial remission after immunosuppressive therapy.

CONCLUSIONS

The patients with anti-SRP antibodies co-occurred with the other MSA may have various clinical characteristics. The clinicopathological phenotypes of these patients seem to be mainly caused by one of the MSAs, namely the responsible antibody.

A systematic review and meta-analysis on the prevalence and clinical characteristics of dysphagia in patients with dermatomyositis

BACKGROUND

Dermatomyositis (DM) is a rare autoimmune disease characterized by distinctive skin rash, muscle inflammation with symmetrical and progressive muscle weakness, and elevated serum levels of muscle-associated enzymes. DM may affect skeletal muscles involved in swallowing, leading to dysphagia, which can negatively impact individual's physical and psychosocial well-being. Despite this, dysphagia in patients with DM remains poorly understood. This systematic review and meta-analysis aimed to evaluate the prevalence and clinical features of dysphagia in patients with DM and juvenile DM (JDM).

METHODS

Four electronic databases were systematically searched until September 2022. Studies with patients with DM or JDM and dysphagia were included. The pooled prevalence of all included studies was calculated, and the clinical characteristics of dysphagia were qualitatively analyzed.

KEY RESULTS

Thirty-nine studies with 3335 patients were included. The overall pooled prevalence of dysphagia was 32.3% (95% CI: 0.270, 0.373) in patients with DM and 37.7% (95% CI: -0.031, 0.785) in patients with JDM. Subgroup analyses revealed that Sweden had the highest prevalence (66.7% [95% CI: 0.289, 1.044]), whereas Tunisia had the lowest prevalence (14.3% [95% CI: -0.040, 0.326]). Moreover, South America had the highest prevalence (47.0% [95% CI: 0.401, 0.538]), whereas Africa had the lowest prevalence (14.3% [95% CI: -0.040, 0.326]). Dysphagia in patients with DM and JDM was characterized by both oropharyngeal and esophageal dysfunctions, with predominant difficulties in motility.

CONCLUSIONS & INFERENCES

Our findings showed that dysphagia affects one in three patients with DM or JDM. However, the documentation on the diagnosis and management of dysphagia in the literature is inadequate. Our results highlighted the need to use both clinical and instrumental assessments to evaluate swallowing function in this population.

Pyomyositis Secondary to Localized Cellulitis in a Dermatomyositis Patient: A Case Report and Review of Infectious Complications in Dermatomyositis

Dermatomyositis (DM) is an autoimmune disorder characterized by proximal muscle weakness and distinct cutaneous features. Unfortunately, infection is a frequent and potentially life-threatening complication in patients with DM. Here, we present a case of pyomyositis in a patient with DM resulting from localized cellulitis. The patient also presented with subcutaneous calcification nodules and dermatomyositis-associated lipodermatosclerosis nodules. To our knowledge, there have been no reports of pyomyositis in patients with DM to date. Furthermore, we reviewed the infectious complications related to DM and polymyositis (PM). We found that idiopathic inflammatory myopathy (IIM) patients exhibit a considerable infection-related mortality rate, ranging from 4.3% to 7.2%. In IIM, infections were identified as the primary cause of mortality in a substantial proportion of cases, accounting for 22.0-83.3% of deaths. These findings have implications for the importance of identifying and managing infections in IIM patients and suggest the need for further research into infection-related complications in these patients.

Autoimmune Idiopathic Inflammatory Myopathies: Pharmacological Differences and Similarities by Type of Myositis and by Sociodemographic Variables

Objective

Autoimmune idiopathic inflammatory myopathies (IIMs) are a group of pathologies that are generally characterized by muscle weakness. Their treatment involves glucocorticoids and immunosuppressants. The aim was to identify differences and similarities in the pharmacological management of a group of patients with autoimmune IIMs according to the type of disease, sex, age group, and city of residence in Colombia from 2020 to 2021.

Methods

This cross-sectional study identified medication prescription patterns for outpatient use in patients with autoimmune IIMs between 2020 and 2021 based on a population database of 8.5 million Colombians affiliated with the Colombian health system. Sociodemographic and pharmacological variables were considered.

Results

A total of 671 patients with autoimmune IIMs were identified, with a median age of 57 years, and 70.9% were women. Overlap myositis was the most frequent disease (31.4%). A total of 91.5% of the patients received pharmacological treatment, mainly systemic glucocorticoids (78.5%), conventional disease-modifying antirheumatic drugs (DMARDs) (74.1%), immunosuppressants (9.1%), and biological DMARDs (3.7%). Pharmacological management predominated among patients with overlap myositis, those who lived in cities, and those affiliated with the contributory regime of the Colombian health system. Conventional DMARDs were prescribed mainly to women and to those older than 65 years.

Conclusions

Patients with autoimmune IIMs are not treated homogeneously. The pattern of drug use varies according to the type of IIM, sex, age group, city, and health system regime affiliation.

Clinical, Serological, and Genetic Characteristics of a Hungarian Myositis-Scleroderma Overlap Cohort

Overlap myositis is a distinct subgroup of idiopathic inflammatory myositis (IIM) with various clinical phenotypes. The aim of this study was to determine the clinical, serological, and genetic features of systemic sclerosis (SSc)-IIM overlap patients. It was a retrospective study using clinical database of 39 patients, fulfilling both the criteria of SSc and IIM. 56.4% of the patients had limited cutaneous, 43.6% had diffuse cutaneous SSc, whereas 7.7% of the patients had dermatomyositis and 92.3% polymyositis. The two diseases occurred simultaneously in 58.97%, while 10.26% in myositis and 30.77% in scleroderma were initially diagnosed. The frequencies of organ involvement were interstitial lung disease 71.8%, dysphagia 66.7%, cardiac involvement 41%, pulmonary arterial hypertension (PAH) 30.8%, and renal involvement 12.8%, respectively. The presence of human leukocyte antigen (HLA) − DRB1∗03 and DQA1∗051∗01 alleles were significantly higher in the overlap patients than in healthy controls (82.35% vs. 27.54%; p < 0.0001 and 88.24% vs. 30.16; p < 0.0001). Certain clinical parameters, such as fever at diagnosis (41.67% vs. 7.41%, p = 0.0046), cardiac involvement (83.33% vs. 22.22%, p = 0.0008), subcutaneous calcinosis (41.66 vs. 11.11, p = 0.01146), and claw hand deformity (25% vs. 11.11%, p = 0.00016) were significantly associated with the presence of PAH. Upon comparison, the overlap patients and anti-Jo-1 positive antisynthetase patients showed similarities in terms of genetic results and major clinical features; however, SSc-IIM overlap patients could be distinguished with higher erythrocyte sedimentation rate (ESR) level, more frequent presence of Raynaud's phenomenon (p < 0.0001; OR: 20.00), dysphagia (p < 0.0001; OR: 15.63), and infrequent livedo reticularis (p < 0.01; OR: 0.11). SSc-IIM overlap myositis is a unique group within IIM-s possessing characteristic clinical features.

Pathophysiological Mechanisms and Treatment of Dermatomyositis and Immune Mediated Necrotizing Myopathies: A Focused Review

Idiopathic inflammatory myopathies (IIM), collectively known as myositis, are a composite group of rare autoimmune diseases affecting mostly skeletal muscle, although other organs or tissues may also be involved. The main clinical feature of myositis is subacute, progressive, symmetrical muscle weakness in the proximal arms and legs, whereas subtypes of myositis may also present with extramuscular features, such as skin involvement, arthritis or interstitial lung disease (ILD). Established subgroups of IIM include dermatomyositis (DM), immune-mediated necrotizing myopathy (IMNM), anti-synthetase syndrome (ASyS), overlap myositis (OM) and inclusion body myositis (IBM). Although these subgroups have overlapping clinical features, the widespread variation in the clinical manifestations of IIM suggests different pathophysiological mechanisms. Various components of the immune system are known to be important immunopathogenic pathways in IIM, although the exact pathophysiological mechanisms causing the muscle damage remain unknown. Current treatment, which consists of glucocorticoids and other immunosuppressive or immunomodulating agents, often fails to achieve a sustained beneficial response and is associated with various adverse effects. New therapeutic targets have been identified that may improve outcomes in patients with IIM. A better understanding of the overlapping and diverging pathophysiological mechanisms of the major subgroups of myositis is needed to optimize treatment. The aim of this review is to report on recent advancements regarding DM and IMNM.

[Clinical and immunological characteristics of 88 cases of overlap myositis]

OBJECTIVE

To investigate the clinical and immunological characteristics of overlap myositis (OM) patients.

METHODS

The data of 368 patients with idiopathic inflammatory myopathies (IIMs) admitted to Peking University People's Hospital from January 2004 to August 2020 were analyzed retrospectively, including demographic characteristics, clinical characteristics (including fever, Gottron' s sign/papules, Heliotrope rash, V-sign, Shawl sign, Mechanic' s hands, skin ulceration, periungual erythema, subcutaneous calcinosis, dysphagia, myalgia, myasthenia, arthritis, Raynaud' s phenomenon, interstitial lung disease, pulmonary hypertension and myocardial involvement), laboratory characteristics, immunological characteristics [including antinuclear antibodies, rheumatoid factors, myositis-associated autoantibodies (MAAs) and myositis-specific autoantibodies (MSAs)] and survival. The clinical and immunological characteristics and prognostic differences of OM and non-OM were compared. The Kaplan-Meier and Log Rank methods were used to analyze the survival.

RESULTS

A total of 368 patients were included. 23.9% (88/368) of IIMs patients were OM patients. Among the 88 OM patients, 85.2% (75/88) of them were female, and the median interval between disease onset and diagnosis was 13.5 months. The incidence of overlapped connective tissue diseases in the OM patients was dermatomyositis (DM) in 60.2%, polymyositis (PM) in 3.4%, immune-mediated necrotizing myopathy (IMNM) in 2.3% and anti-synthetase syndrome (ASS) in 34.1%. Compared with the non-OM patients, the proportion of the females in the OM patients was higher (85.2% vs. 72.1%, P=0.016), the OM patients had longer disease duration [13.5(4.5, 48.0) months vs. 4.0(2.0, 12.0) months, P < 0.001]. As for clinical characteristics, compared with the non-OM patients, the incidence of V-sign (25.0% vs. 44.6%, P=0.001) and periungual erythema (8.0% vs. 19.6%, P=0.013) were lower; the incidence of Raynaud's phenomenon (14.8% vs. 1.8%, P < 0.001), interstitial pneumonia (88.6% vs. 72.1%, P=0.001), pulmonary hypertension (22.7% vs. 7.5%, P < 0.001) and myocardial involvement (18.2% vs. 9.3%, P=0.033) were higher. As for immunological characteristics, compared with the non-OM patients, the incidence of elevated aspartate aminotransferase (AST) (31.8% vs. 45.0%, P=0.035) was lower and elevated C-reactive protein (CRP) (58.0% vs. 44.6%, P=0.037) was higher; the positive rates of antinuclear antibodies (ANA) (85.1% vs. 63.4%, P=0.001) and rheumatoid factors (RF) (40.2% vs. 17.8%, P < 0.001) and anti-Ro-52 (71.6% vs. 56.1%, P=0.038) in serum were higher. There was no significant difference in the survival between the OM patients and non-OM patients.

CONCLUSION

Pulmonary hypertension and myocardial involvement were frequently observed in OM.

Association between clinical phenotypes of dermatomyositis and polymyositis with myositis-specific antibodies and overlap systemic autoimmune diseases

The aim of this study was to evaluate the association between clinical phenotypes of dermatomyositis (DM) and polymyositis (PM) with myositis-specific antibodies (MSAs), and overlap diagnosis of systemic autoimmune diseases.This cross-sectional study was conducted on 67 patients with DM and 27 patients with PM recruited from a regional hospital in southern Taiwan. Clinical phenotypes of DM and PM were assessed and MSAs were measured using a commercial line blot assay. The association of clinical phenotypes of DM and PM with MSAs and overlap diagnosis of systemic autoimmune diseases was performed using univariate and multiple logistic regression analyses.Clinically, patients with DM and PM and overlap diagnosis of systemic sclerosis were associated with a higher risk of interstitial lung diseases (ILDs) (odds ratio [OR] = 6.73; P = .048), Raynaud phenomenon (OR = 7.30; P = .034), and malignancy (OR = 350.77; P = .013). The risk of malignancy was also associated with older age (OR 1.31; P = .012), and male patients were associated with a higher risk of fever. For MSAs, anti-aminoacyl-tRNA synthetase antibodies were associated with ILD, antinuclear antibody were associated with a lower risk of arthritis, anti-transcription intermediary factor 1-gamma antibodies were associated with milder symptoms of muscle weakness, anti-Ku antibodies were associated with overlap diagnosis of systemic lupus erythematosus, and anti-Ro52 antibodies were associated with the development of Raynaud phenomenon and Sjögren syndrome.MSAs and overlap diagnosis of systemic sclerosis were significantly associated with clinical phenotypes of DM and PM. Physicians should be vigilant for malignancy in older DM and PM patients with overlap diagnosis of systeic sclerosis. The possibility of developing ILD in patients with overlap diagnosis of systemic sclerosis or serum positivity of anti-aminoacyl-tRNA synthetase antibodies should be considered.

Idiopathische inflammatorische Myopathien: Aktuelles zu Diagnose und Klassifikation

Auf dem Sektor der Kollagenosen ist der wissenschaftliche Fortschritt bei der Myositis in den letzten 15–20 Jahren bemerkenswert. Durch kontinuierliche Forschung und intensive Vernetzung der Myositis-Experten ist es gelungen, neue Untergruppen zu identifizieren und somit für die Prognose wichtige Organmanifestationen rechtzeitig zu erkennen. Vor dem Hintergrund dieser Neuerungen verfolgt diese Übersichtsarbeit sowohl das Ziel, möglichst alle Facetten der Erkrankung zu präsentieren, als auch die moderne Einteilung der idiopathischen inflammatorischen Myopathien zu erläutern. Außerdem werden die neuen Klassifikationskriterien vorgestellt, die die Kriterien von Bohan und Peter aus dem Jahr 1975 abgelöst haben. Im Artikel werden ihre Stärken und Schwächen sowie ihr Optimierungspotenzial diskutiert.

Comparison of the 2017 EULAR/ACR Criteria with Clinicoserologic Criteria for the Classification of Idiopathic Inflammatory Myopathies in Korean Patients

PURPOSE

To investigate correlations between myositis-specific autoantibodies (MSA) or myositis-associated antibodies (MAA) and clinical features, thereby demonstrating the utility of clinicoserologic classification in idiopathic inflammatory myopathies (IIM) patients.

MATERIALS AND METHODS

We conducted a multicenter study of 108 adult patients (age ≥18 years) who were diagnosed with IIM by Peter and Bohan criteria or 2004 European Neuromuscular Centre (ENMC) criteria. Clinical data were obtained by medical record review. Immunoblot assay with Euroline strip (EUROIMMUN, Germany) was performed using the sera of dermatomyositis (DM, n=56), polymyositis (PM, n=45), amyopathic DM (n=5), DM sine dermatitis (n=1), and immune mediated necrotizing myopathy (n=1) patients. Patients were classified based on two classifications: 2017 EULAR/ACR and novel clinicoserologic classification.

RESULTS

According to 2017 EULAR/ACR criteria, DM and PM were the most and the second most frequent entities. Overlap myositis was the major entity of IIM, and the frequency of PM was significantly lower when applying clinicoserologic classification criteria. Sixty-nine (63.9%) patients had one or more MSA, and 61 (56.5%) patients had one or more MAA. Interstitial lung disease was closely associated with anti-MDA5 and anti-ARS, and DM-specific skin lesions were frequently observed in patients with anti-TIF1γ, anti-SRP, and anti-MDA5.

CONCLUSION

The clinicoserologic criteria based on MSA/MAA positivity could reflect more precise clinical features of IIM. Establishment of a laboratory system routinely available to screen for MSA/MAA status will be beneficial to provide precise diagnosis and proper management of IIM patients.

Characteristics and outcomes of overlap myositis: a comparative multigroup cohort study in adults from the MyoCite cohort

Overlap myositis (OM), an important subset of idiopathic inflammatory myopathies (IIM), is being increasingly recognized with wider myositis-specific autoantibody (MSA) testing. We studied the differences in clinical characteristics and long-term outcomes of OM with Dermatomyositis (DM), Polymyositis (PM), anti-synthetase syndrome (ASSD), and Cancer-associated IIM (CAM). Data from the MyoCite registry (Dec2017-May2020), a prospective dataset of IIM was extracted for the clinical profile, and MSAs, immunosuppressants received, disease activity (relapses and incomplete response), and treatment-related (drugs ADRs and infections) adverse events (DRAE and TRAE) were collected and analyzed between groups. Of 214 adults (58-OM,89-DM,27-ASSD,33-PM,7-CAM), OM had a greater female preponderance (13.5:1). Raynaud's and sclerodactyly were the prime distinguishing features of OM. OM could be distinguished from PM by frequent arthritis (OR-3.2) and infrequent dysphagia (OR-0.17); DM with greater nephritis (OR-20), infrequent dysphagia (OR-0.24) and rashes (OR-0.02); and ASSD by infrequent ILD (OR-0.07), and mechanic's hand (OR-0.05). 50% fulfilled the classification criteria for ASSD in the absence of MSA testing. ANA was positive more often (PM/DM: OR-6.7) and anti-Ro52 (OR-4.5) frequent in OM. Baseline serum creatinine and acute phase reactants were higher. OM received lower glucocorticoids (0 mg/kg, p < 0.001). Overall, 90% and 84% of OM at 12 and 24 months, respectively, achieved remission, with similar DRAE and TRAE as other IIM subsets. OM can be misdiagnosed as ASSD in the absence of MSA testing. Raynaud's, sclerodactyly, and a positive ANA may identify OM and prevent overtreatment.

The spectrum of idiopathic inflammatory myopathies in South Africa

INTRODUCTION

There are many reports on idiopathic inflammatory myopathies (IIM) but little information from sub-Saharan Africa. We conducted a retrospective study of IIM in a multi-ethnic cohort seen at a single centre in Durban, South Africa.

METHOD

The study included patients who fulfilled the Bohan and Peter or European League Against Rheumatism/American College of Rheumatology criteria for IIM. The information recorded included demographic data, clinical findings, results of investigations, treatment and outcome. Patients with overlap myositis (OM) had myositis and criteria for another connective tissue disease.

RESULTS

There were 104 patients with IIM; 82.7% female and 70.2% African blacks. They included 41 (39.4%) with OM, 26 (25%) polymyositis (PM), 26 (25%) dermatomyositis (DM), six (5.8%) juvenile dermatomyositis and five (4.8%) cancer-associated myositis. Our patients had a younger mean age at diagnosis (36.8 ± 14.7 years) compared with 45-55 years in most other studies. Scleroderma-myositis overlap accounted for 26 (63.4%) of the patients with OM. Patients with OM were significantly younger than PM (p = 0.004) and DM (p = 0.044) and had lower, but not statistically significant, creatine kinase levels at diagnosis compared with PM (p = 0.052) and DM (p = 0.073). Interstitial lung disease was more common in OM (p = 0.001) and PM (p = 0.024) than DM. Oropharyngeal weakness was more common in DM than OM (p = 0.001) and PM (p = 0.032). African blacks were younger (p = 0.028) at diagnosis and had more cardiac abnormalities (p = 0.034) than Indians.

CONCLUSION

The spectrum of IIM in our cohort of mainly African blacks is similar to other studies, with OM being the most frequent subtype. Key Points • As there is limited information on idiopathic inflammatory myopathies (IIM) in sub-Saharan Africa, this study reports the spectrum of IIM in a South African cohort of predominantly African blacks. • Our patients were younger at diagnosis, and overlap myositis was the most common phenotype. • Comparisons with other studies show similarities in the manifestations of IIM.

Arthritis in Idiopathic Inflammatory Myopathies

PURPOSE OF REVIEW

Arthritis is a well-recognized symptom of idiopathic inflammatory myopathies (IIM). We provide a summary of available data regarding the epidemiology, clinical characteristics, and autoantibody associations of joint involvement in various forms of IIM.

RECENT FINDINGS

Arthritis is reported in 18-55% of patients with IIM. It is particularly frequent (20-70%) in those with antisynthetase syndrome (ASS); highest prevalence is associated with anti-Jo-1 positivity. Most common manifestation is non-erosive polyarthritis. X-ray erosions may be found occasionally in ASS, particularly in patients with overlap with rheumatoid arthritis (RA). Arthritis is often present at the time of IIM diagnosis and it may even precede the onset of muscle weakness. Arthritis may in some cases be the main disease manifestation responsible for the disease burden in patients with IIM. Arthritis is a frequent symptom of IIM. Polyarthritis of small joints of the hands is the most frequent clinical manifestation. Arthritis may be the first or dominant symptom in IIM and therefore patients may be initially misdiagnosed as having RA. Particularly in seronegative RA patients with interstitial lung disease or Raynaud's phenomenon, the possibility of IIM should be considered.