Clinical characteristics of patients with myositis and autoantibodies to different fragments of the Mi-2 beta antigen

Cancer and myositis: new insights into an old association

PURPOSE OF REVIEW

The association between the idiopathic inflammatory myopathies and the development of malignancy has been appreciated for nearly a century, but its meaning and significance have remained unclear. Significant advances in our understanding of the epidemiology and pathophysiology of this association have recently been made. This review will describe the major epidemiological evidence linking inflammatory myopathies with cancer, and will use this evidence to highlight a recently proposed model for the development of cancer-associated myositis.

RECENT FINDINGS

The temporal relationship between the development of cancer and myositis is reminiscent of that seen in neurological paraneoplastic disorders, in which antigens targeted for an immune response are expressed at high levels in the inciting tumor and the affected neuronal tissue. It has also recently been observed that regenerating cells in myositis muscle, but not its normal counterpart, express high levels of myositis-specific autoantigens. These same antigens are expressed at high levels in several cancers known to be associated with the development of myositis, but not in corresponding normal tissue.

SUMMARY

These observations suggest a model of paraneoplasia focusing on common autoantigen expression and immune targeting between cancer tissues and muscle tissue in myositis.

Update on Connective Tissue Diseases in Dermatology

Recent advances in understanding the pathogenesis of autoimmune diseases, including lupus erythematosus, dermatomyositis, and scleroderma, have allowed for reorganization of the classification of these disorders. With these novel stratifications, early identification of rheumatic skin diseases with systemic implications and consistency in designing and executing therapeutic trials will be enhanced. This review will provide a compilation of updates on epidemiology, pathology, evaluation, and classification with a predominant focus on therapeutics, reflecting the growth is this area.

Contribution of autoantibodies to the diagnosis and nosology of inflammatory muscle disease

The myositides are systemic autoimmune conditions of which the most important are polymyositis, dermatomyositis, and inclusion body myositis. In addition to the classic clinical diagnostic criteria, myositis-specific autoantibodies were identified about 15 years ago. Among the dozen or so myositis-specific autoantibodies reported to date, the most characteristic are directed against cytoplasmic antigens, such as tRNA synthetase (Jo-1 or PL-1, PL-7, PL-12, EJ, OJ, JS, and KS), signal-recognition particle (SRP), Mas, KJ, Fer (eEF1), and Wa. Antibodies to nuclear antigens include anti-Mi-2, anti-PMS (PMS1, and PMS2), and related antibodies (MLH1, DNA protein kinase catalytic subunit (DNA PKCS)...), and anti-56 kDa. Myositis-associated antibodies are not specific but may be found in patients with myositis. They are directed to nuclear or nucleolar antigens such as PM-Scl, Ku, RNP (U1-RNP and U2-RNP, U4/U6-RNP, and U5-RNP), Ro 52 kDa and, more rarely, Ro 60 kDa and La. Myositis-specific antibodies have proved useful on two fronts. They have improved the diagnosis of myositis by leading to the identification of characteristic clinical patterns, such as anti-synthetase syndrome. The place of autoantibodies alongside classic clinical and laboratory criteria remains to be determined, however. First, standardized assays will have to be developed to replace current detection methods, which use widely variable techniques and antigen preparations. Myositis-specific antibodies have also shed light on the pathogenesis of myositis. For instance, the development of antibodies to tRNA synthetases constitutes an original autoimmunity model that shows how muscle damage, probably of a nonspecific nature, can lead to the production of autoantibodies that perpetuate and aggravate the muscle lesions.

Myositis specific autoantibodies

Recent studies have continued to examine the clinical associations of the group of autoantibodies that occurs predominantly in patients who have myositis (antibodies to aminoacyl-tRNA synthetases, to signal recognition particle [SRP], and to the nuclear helicase Mi-2). The anti-synthetase syndrome has been further studied, and the value of tacrolimus in treatment of the associated interstitial lung disease has been noted. The low frequency of myositis specific autoantibodies in non-myositis neuromuscular disorders has been more clearly demonstrated. The clinical associations of anti-Mi-2 and anti-SRP were further studied, and patients with antibodies without myositis were reported. Evidence suggested that ultraviolet light exposure may influence the expression of dermatomyositis and anti-Mi-2. A new classification for myositis using overlap clinical features and autoantibodies was proposed. A new autoantibody, anti-caDM-140, was described, associated with clinically amyopathic dermatomyositis and interstitial lung disease. The possibility was raised that increased antigen expression in regenerating muscle may help to perpetuate the disease. These antibodies continue to be the subject of active investigation.