Real world utilization of the myositis autoantibody panel

External validation of the 2017 ACR/EULAR classification criteria for inflammatory myopathies in a Mexican cohort: Role of autoantibodies in the diagnosis and classification of patients with inflammatory myopathies

OBJECTIVE

This retrospective study aimed to perform the first external validation of the ACR/EULAR classification criteria for inflammatory myopathy (IIM) in a Mexican dynamic cohort where the patients were evaluated with clinical and laboratory values. As secondary objectives, we presented the clinical characteristics of the patients and included antibodies other than anti Jo1 to evaluate their impact on our population.

METHODOLOGY

This study included 70 patients with IIM and 70 patients with differential diagnoses of IIM, according to the absolute score of the classification criteria. We obtained sensitivity and specificity in the modality without biopsy, and as an exploratory analysis, we added other antibodies from the myositis extended panel. We analyzed the area under the curve (AUC) of three models: score without antibodies, with anti Jo1 and with any antibody.

RESULTS

The ACR/EULAR criteria showed increased specificity and at least similar sensitivity to that of the original cohort (85% sensitivity and 92% specificity), with a cohort point of >55%. When we classified patients into definite, probable, possible, and no IIM categories, by adding the extended myopathy panel, 6 of the 10 patients initially classified as "no IIM" changed their classification to "Probable IIM" and 4 to "Definite IIM"; of the 16 patients classified as "probable IIM," 15 changed their classification to "Definite IIM."

CONCLUSION

Considering the limitations of this study, we concluded that the 2017 EULAR/ACR criteria for IIM classification are sensitive and specific for classifying patients with IIM in the Mexican population. Additionally, the addition of antibodies other than anti-Jo1 may improve performance in certain populations.

Statin-induced autoimmune myositis: a proposal of an "experience-based" diagnostic algorithm from the analysis of 69 patients

Statin-induced autoimmune myositis (SIAM) represents a rare clinical entity that can be triggered by prolonged statin treatment. Its pathogenetic substrate consists of an autoimmune-mediated mechanism, evidenced by the detection of antibodies directed against the 3-hydroxy-3-methylglutaryl-coenzyme A reductase (anti-HMGCR Ab), the target enzyme of statin therapies. To facilitate the diagnosis of nuanced SIAM clinical cases, the present study proposes an "experience-based" diagnostic algorithm for SIAM. We have analyzed the clinical data of 69 patients diagnosed with SIAM. Sixty-seven patients have been collected from the 55 available and complete case records regarding SIAM in the literature; the other 2 patients represent our direct clinical experience and their case records have been detailed. From the analysis of the clinical features of 69 patients, we have constructed the diagnostic algorithm, which starts from the recognition of suggestive symptoms of SIAM. Further steps provide for CK values dosage, musculoskeletal MR, EMG/ENG of upper-lower limbs and, Anti-HMGCR Ab testing and, where possible, the muscle biopsy. A global evaluation of the collected clinical features may suggest a more severe disease in female patients. Atorvastatin proved to be the most used hypolipidemic therapy.

Myositis-Specific and Myositis-Associated Antibodies in Fibromyalgia Patients: A Prospective Study

Fibromyalgia (FM) is a common rheumatologic disorder characterised by widespread muscular pain. Myalgia is also a common clinical feature in Connective Tissue Disease (CTD), and FM should be studied for the concomitant presence of a CTD. The aim of this study is to evaluate the prevalence of Myositis-Specific and Myositis-Associated Antibodies (MSA/MAA) in a cohort of FM patients. We enrolled 233 consecutive FM patients (defined according to the 2016 criteria) that did not report clinical signs of autoimmune disorders and followed them for at least one year. The patients were tested for MSA/MAA with immunoblotting. FM patients were seropositive for Antinuclear Antibodies (ANA) in 24% of cases, for MSA in 9%, and for MAA in 6%. A specific diagnosis of CTD was made in 12 patients (5.2%), namely, 5 cases of primary Sjögren’s Syndrome and 7 of Idiopathic Inflammatory Myopathy. Seropositive patients showed clinical features similar to those who were seronegative at baseline. A CTD diagnosis was associated with ANA positivity (p = 0.03, X2 4.9), the presence of a speckled pattern (p = 0.02, X2 5.3), positivity for MAA (p = 0.004, X2 8.1), and MSA (p = 0.003, X2 9.2). In conclusion, a non-negligible proportion of FM patients may be seropositive for MSA/MAA, and that seropositivity might suggest a diagnosis of CTD.

A New Method for the Assessment of Myalgia in Interstitial Lung Disease: Association with Positivity for Myositis-Specific and Myositis-Associated Antibodies

In this study, it was found that myositis-specific and myositis-associated antibodies (MSAs and MAAs) improved the recognition of idiopathic inflammatory myopathies (IIMs) in interstitial lung disease (ILD) patients. The objective of this study is to propose a clinical method to evaluate myalgia in respiratory settings as a possible tool for the recognition of MSA/MAA positivity in ILD patients. We prospectively enrolled 167 ILD patients with suspected myositis, of which 63 had myalgia evoked at specific points (M+ILD+). We also enrolled in a 174 patients with only myalgia (M+ILD-) in a rheumatological setting. The patients were assessed jointly by rheumatologists and pulmonologists and were tested for autoantibodies. M+ILD+ patients were positive for at least one MAA/MSA in 68.3% of cases, as were M-ILD+ patients in 48.1% of cases and M+ILD- patients in 17.2% of cases (p = 0.01 and <0.0001, respectively). A diagnosis of IIM was made in 39.7% of M+ILD+ patients and in 23.1% of the M-ILD+ group (p = 0.02). Myalgia was significantly associated with positivity for MSA/MAAs in ILD patients (p = 0.01, X2: 6.47). In conclusion, myalgia in ILD patients with suspected myositis is associated with MSA/MAA positivity, and could support a diagnosis of IIM. A significant proportion of M+ILD- patients also had MSA/MAA positivity, a phenomenon warranting further study to evaluate its clinical meaning.

Clinical features and diagnostic tools in idiopathic inflammatory myopathies

Idiopathic inflammatory myopathies (IIMs) are rare autoimmune disorders affecting primarily muscles, but other organs can be involved. This review describes the clinical features, diagnosis and treatment for IIMs, namely polymyositis (PM), dermatomyositis (DM), sporadic inclusion body myositis (sIBM), immune-mediated necrotizing myopathy (IMNM), and myositis associated with antisynthetase syndrome (ASS). The diagnostic approach has been updated recently based on the discovery of circulating autoantibodies, which has enhanced the management of patients. Currently, validated classification criteria for IIMs allow clinical studies with well-defined sets of patients but diagnostic criteria to guide the care of individual patients in routine clinical practice are still missing. This review analyzes the clinical manifestations and laboratory findings of IIMs, discusses the efficiency of modern and standard methods employed in their workup, and delineates optimal practice for clinical care. Α multidisciplinary diagnostic approach that combines clinical, neurologic and rheumatologic examination, evaluation of electrophysiologic and morphologic muscle characteristics, and assessment of autoantibody immunoassays has been determined to be the preferred approach for effective management of patients with suspected IIMs.