Polymyositis: an ongoing discussion about a disease entity

Polymyositis: does it really exist as a distinct clinical subset?

PURPOSE OF REVIEW

To summarize information on polymyositis; diagnosis, definitions, published data and opinions.

RECENT FINDINGS

Polymyositis originally referred to inflammatory muscle diseases presenting with muscle weakness and inflammatory cell infiltrates on muscle tissue visible by microscopy. Over time and with improved technology to immunophenotype infiltrating inflammatory cells and characterize muscle fibres, the meaning of polymyositis changed and became more specific. There is ongoing controversy over the term polymyositis, with proponents for a strict definition based on histopathological and immunohistochemical features on muscle biopsies whereas others advocate for a broader clinical and histopathological phenotype. Over the past decades, the discovery of several myositis-specific autoantibodies together with distinct histopathological features have enabled the identification of new subsets previously labelled as polymyositis notably the antisynthetase syndrome and the immune-mediated necrotizing myopathies thus reducing the number of patients classified as polymyositis.

SUMMARY

There are still a small number of patients among the idiopathic inflammatory myopathies that can be classified as polymyositis as discussed in this review but the entity is now considered relatively rare.

Biomarker und Histologie bei idiopathischen inflammatorischen Myopathien

Die idiopathischen inflammatorischen Myopathien (IIM) sind eine Gruppe entzündlicher Muskelerkrankungen für deren Diagnosestellung, Verlaufsbeurteilung, Prognoseabschätzung und Risikostratifizierung Biomarker eine jeweils essentielle Rolle spielen. Biomarker in diesem Kontext können sowohl „herkömmliche“ serologische Marker wie Muskelenzyme oder Autoantikörper, histologische Marker wie entitätsspezifische inflammatorische Muster, aber auch genomische und genetische Marker sein. Der vorliegende Artikel gibt einen Überblick über bewährte und innovative Marker.

Development of a New Classification System for Idiopathic Inflammatory Myopathies Based on Clinical Manifestations and Myositis-Specific Autoantibodies

Importance

Idiopathic inflammatory myopathies are heterogeneous in their pathophysiologic features and prognosis. The emergence of myositis-specific autoantibodies suggests that subgroups of patients exist.

Objective

To develop a new classification scheme for idiopathic inflammatory myopathies based on phenotypic, biological, and immunologic criteria.

Design, Setting, and Participants

An observational, retrospective cohort study was performed using a database of the French myositis network. Patients identified from referral centers for neuromuscular diseases were included from January 1, 2003, to February 1, 2016. Of 445 initial patients, 185 patients were excluded and 260 adult patients with myositis who had complete data and defined historical classifications for polymyositis, dermatomyositis, and inclusion body myositis were enrolled. All patients were tested for anti-histidyl-ARN-t- synthetase (Jo1), anti-threonine-ARN-t-synthetase (PL7), anti-alanine-ARN-t-synthetase (PL12), anti-complex nucleosome remodeling histone deacetylase (Mi2), anti-Ku, anti-polymyositis/systemic scleroderma (PMScl), anti-topoisomerase 1 (Scl70), and anti-signal recognition particle (SRP) antibodies. A total of 708 variables were collected per patient (eg, cancer, lung involvement, and myositis-specific antibodies).

Main Outcomes and Measures

Unsupervised multiple correspondence analysis and hierarchical clustering analysis to aggregate patients in subgroups.

Results

Among 260 participants (163 [62.7%] women; mean age, 59.7 years; median age [range], 61.5 years [48-71 years]), 4 clusters of patients emerged. Cluster 1 (n = 77) included patients who were male, white, and older than 60 years and had finger flexor and quadriceps weakness and findings of vacuolated fibers and mitochondrial abnormalities. Cluster 1 regrouped patients who had inclusion body myositis (72 of 77 patients [93.5%]; 95% CI, 85.5%-97.8%; P < .001). Cluster 2 (n = 91) regrouped patients who were women and had high creatine phosphokinase levels, necrosis without inflammation, and anti-SRP or anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) antibodies corresponding to immune-mediated necrotizing myopathy (53 of 91 [58.2%]; 95% CI, 47.4%-68.5%; P < .001). Cluster 3 (n = 52) regrouped patients who had dermatomyositis rash and anti-Mi2, anti-melanoma differentiation-associated protein 5 (MDA5), or anti-transcription intermediary factor-1γ (TIF1γ) antibodies, mainly corresponding with patients who had dermatomyositis (43 of 52 [82.7%]; 95% CI, 69.7%-91.8%; P < .001). Cluster 4 (n = 40) was defined by the presence of anti-Jo1 or anti-PL7 antibodies corresponding to antisynthetase syndrome (36 of 40 [90.0%]; 95% CI, 76.3%-97.2%; P < .001). The classification of an independent cohort (n = 50) confirmed the 4 clusters (Cohen κ light, 0.8; 95% CI, 0.6-0.9).

Conclusions and Relevance

These findings suggest a classification of idiopathic inflammatory myopathies with 4 subgroups: dermatomyositis, inclusion body myositis, immune-mediated necrotizing myopathy, and antisynthetase syndrome. This classification system suggests that a targeted clinical-serologic approach for identifying idiopathic inflammatory myopathies may be warranted.

Immune and myodegenerative pathomechanisms in inclusion body myositis

Inclusion Body Myositis (IBM) is a relatively common acquired inflammatory myopathy in patients above 50 years of age. Pathological hallmarks of IBM are intramyofiber protein inclusions and endomysial inflammation, indicating that both myodegenerative and inflammatory mechanisms contribute to its pathogenesis. Impaired protein degradation by the autophagic machinery, which regulates innate and adaptive immune responses, in skeletal muscle fibers has recently been identified as a potential key pathomechanism in IBM. Immunotherapies, which are successfully used for treating other inflammatory myopathies lack efficacy in IBM and so far no effective treatment is available. Thus, a better understanding of the mechanistic pathways underlying progressive muscle weakness and atrophy in IBM is crucial in identifying novel promising targets for therapeutic intervention. Here, we discuss recent insights into the pathomechanistic network of mutually dependent inflammatory and degenerative events during IBM.

Amyopathic Dermatomyositis: A Concise Review of Clinical Manifestations and Associated Malignancies

Amyopathic dermatomyositis is a rare, idiopathic, connective tissue disease that presents with dermatologic lesions of classic dermatomyositis but lacks the myopathy of this disease. Cutaneous manifestations may include Gottron's sign, heliotrope rash, and characteristic patterns of poikiloderma. There is a substantial risk for developing interstitial lung disease or malignancy in patients with amyopathic dermatomyositis. A literature review of amyopathic dermatomyositis was performed using the PubMed medical database. The key features of amyopathic dermatomyositis, including autoantibodies, clinical presentation and dermatologic manifestations, epidemiology, history, associated malignancies, management, and pathogenesis, are summarized in this review. Cancer (solid tumor) (73/79, 89 %) and hematologic malignancies (9/79, 11 %) were reported in 79 patients, with three patients having more than one malignancy. In addition, there were six patients with amyopathic dermatomyositis who had tumor of unknown primary, and eight patients with cancer-associated amyopathic dermatomyositis for whom no additional details were provided. From the group of 73 tumors for whom primary origin and sex were available, malignancy of the genitourinary organs (24/73, 33 %), aerorespiratory organs (15/73, 21 %), and breast (14/73, 19 %) were the most commonly observed solid organ tumors. Tumors of the genitourinary organs (15/48, 31 %) and breast (14/48, 29 %) were the most frequent neoplasms in women, accounting for 29 of 48 (60 %) cancers, with the most common sites being breast (14/48, 29 %), ovary (8/48, 17 %), and cervix or uterus (5/48, 10 %). In men, tumors of the aerorespiratory (9/25, 36 %) and genitourinary (9/25, 36 %) tracts were the most common neoplasms, accounting for 72 % (18/25) of cancers; the most common sites of primary malignancy were nasopharyngeal (6/25, 24 %), bladder (4/25, 16 %), and either colorectal, lung or prostate cancer (three cancers each, 12 %). In summary, the search for an undiagnosed associated malignancy in patients with amyopathic dermatomyositis should focus towards the organs most frequently affected. Similar to classic dermatomyositis, ovarian and nasopharyngeal cancers are also common in amyopathic dermatomyositis. However, in contrast to lung cancer, which is the most frequent malignancy associated with classic dermatomyositis, breast cancer was the most common type of malignancy reported in patients with amyopathic dermatomyosotis.

Polymyositis-dermatomyositis recognized during the follow-up of a patient with type 2 diabetes

Polymyositis-dermatomyositis is a rare systemic autoimmune disease which belongs to the class of idiopathic inflammatory myopathies. The disease exhibits high inter-individual variability, but chronic myositis is a common feature. As different manifestations often appear in atypical forms, establishing the precise diagnosis can be rather complicated. The prognosis and the patient’s life expectations highly depend on whether the clinician considers this possibility in the diagnostic process or not. The authors present the case of a 50-year-old woman who was referred to hospital with suspected myopathy by her general practitioner. The history of the patient, the overall clinical picture and some marked laboratory abnormalities raised the possibility of polymyositis-dermatomyositis, which was unequivocally confirmed by immunological tests. Drug therapy was started immediately with the administration of high dose corticosteroid (1–2 mg/kg/day methylprednisolone), which was found to be an effective strategy leading to fast and remarkable improvement in the patient’s condition. From the first hospital day, the patient also received insulin therapy in order to prevent any potential corticosteroid-induced imbalance in her carbohydrate metabolism. The long-term patient management was provided by an interdisciplinary team the members of which (both clinicians and other health care professionals) worked according to a co-ordinated, complex care plan, and managed not only the “physiological functions” but the different psychological and social problems as well, which are usually associated with the disease. The follow-up period of this polyphase disease process lasted for 4.5 years, during which only two relapses occurred, and muscle strength typically varied between 3 and 4 on a five grade scale with the exception of the relapse periods. Good outcome was attributed to the strict follow-up and individualized therapy/care. Orv. Hetil., 2012, 153, 467–474.

How citation distortions create unfounded authority: analysis of a citation network

OBJECTIVE

To understand belief in a specific scientific claim by studying the pattern of citations among papers stating it.

DESIGN

A complete citation network was constructed from all PubMed indexed English literature papers addressing the belief that beta amyloid, a protein accumulated in the brain in Alzheimer's disease, is produced by and injures skeletal muscle of patients with inclusion body myositis. Social network theory and graph theory were used to analyse this network.

MAIN OUTCOME MEASURES

Citation bias, amplification, and invention, and their effects on determining authority.

RESULTS

The network contained 242 papers and 675 citations addressing the belief, with 220,553 citation paths supporting it. Unfounded authority was established by citation bias against papers that refuted or weakened the belief; amplification, the marked expansion of the belief system by papers presenting no data addressing it; and forms of invention such as the conversion of hypothesis into fact through citation alone. Extension of this network into text within grants funded by the National Institutes of Health and obtained through the Freedom of Information Act showed the same phenomena present and sometimes used to justify requests for funding.

CONCLUSION

Citation is both an impartial scholarly method and a powerful form of social communication. Through distortions in its social use that include bias, amplification, and invention, citation can be used to generate information cascades resulting in unfounded authority of claims. Construction and analysis of a claim specific citation network may clarify the nature of a published belief system and expose distorted methods of social citation.

Advances in the therapy of idiopathic inflammatory myopathies

PURPOSE OF REVIEW

To review progress in areas pertinent to the development of better therapies for the idiopathic inflammatory myopathies.

RECENT FINDINGS

New classification criteria for the idiopathic inflammatory myopathies have been proposed in an effort to define disease subsets with more uniform prognoses and responses to therapy. Diseases that may mimic the idiopathic inflammatory myopathies can be differentiated more accurately with molecular testing and biochemical and immunohistochemical analysis of muscle tissue. Advances in our understanding of the pathogenesis of the idiopathic inflammatory myopathies have served to identify potential new therapeutic targets. International collaborative study groups have reached consensus on outcome measures and on the optimal design of clinical trials in the idiopathic inflammatory myopathies. Tumor necrosis factor-alpha antagonists, rituximab, and the calcineurin inhibitors are being used to treat the idiopathic inflammatory myopathies, but their efficacy has not yet been tested in randomized clinical trials.

SUMMARY

Future advances in the development of therapies for the idiopathic inflammatory myopathies have been enabled by recent progress in myositis classification, differential diagnosis, basic science, and clinical trial design. Preliminary studies suggest that calcineurin inhibitors, tumor necrosis factor antagonists, and rituximab may be effective treatments.

Muscle Involvement in Mixed Connective Tissue Disease

Muscle disease has been recognized as a common feature of mixed connective tissue disease (MCTD) since its first description in 1972. In the absence of clinical trials that are directed specifically at the myositis of MCTD, patients should be treated in the manner that is recommended for other forms of myositis. Myositis of MCTD may have a better prognosis than other forms of myositis.

Advances in diagnosis and management of inflammatory myopathies

Idiopathic inflammatory myopathies are rare causes of muscle weakness and may be difficult to diagnose and manage. The traditional classification of polymyositis (PM) and dermatomyositis (DM) has been expanded to include inclusion body myositis (IBM) and several other types as our knowledge of underlying immunopathologic mechanisms, specific antibodies, and clinical features has advanced. This has led to several modified and new classification systems and also to controversies over specific criteria required to make diagnoses of the several forms of inflammatory myopathies. The clinical response to treatment of PM and DM has been largely empiric, and IBM has proven to be refractory. There are efforts to formalize objective measures of treatment response to aid future randomized, controlled trials. This article reviews new information in the field of idiopathic inflammatory myopathies from the neurologic clinical perspective.