Identifying myositis-specific and myositis-associated antibodies is important for determining subclasses of idiopathic inflammatory myopathies so that appropriate and timely therapy can be initiated, judging from findings from a retrospective study of 169 patients.
Researchers examined the sera from 130 patients who had been initially classified as having primary myositis, and from another 39 patients who had been classified as having overlap myositis (systemic sclerosis , rheumatoid arthritis , systemic lupus erythematosus  and Sj gren's syndrome ).
The initial classifications were made using original Bohan and Peter criteria, which are commonly used for classifying idiopathic inflammatory myopathy patients, but which don't take into consideration the presence of myositis-specific and myositis-associated antibodies.
Reevaluation of these patients based on the presence of myositis-specific and -associated antibodies led to 11 (8.5%) of the patients in the primary myositis group being reclassified as having overlap myositis. That classification means that the patients also fulfilled revised American College of Rheumatology criteria for systemic lupus erythematosus, rheumatic arthritis, systemic sclerosis, or Sj gren's syndrome, said Dr. Andrea V ncsa of the University of Debrecen Medical and Health Science Center (Hungary) and colleagues.
In addition to determining the prevalence of various myositis-specific and myositis-associated antibodies, the investigators also identified the clinical characteristics, disease course, and response to therapy associated with the antibodies. Myositis-specific antibodies included anti–Jo-1, –PL-7, –PL-12, –Mi-2, and –SRP. Myositis-associated antibodies included anti–SS-A, –SS-B, –U1snRNP, –Pm/Scl, and –Ku. The investigators characterized the patients into different clinicoserologic groups based on whether myositis-specific and myositis-associated antibodies were present, and further classified the patients as having polymyositis or dermatomyositis (Joint Bone Spine 2010 Feb. 24 [doi:10.1016/j.jbspin.2009.0.008]).
The researchers found that polymyositis was the most common myositis in overlap disease, occurring in 87% of patients in that group. Scleroderma was the most common overlapping disease, occurring in a third of patients in that group.
Antinuclear antibodies (ANA) were present in about 62% of overlap patients, compared with 25% of the primary myositis patients. ANA positivity was associated with an increased risk of associated connective tissue disease (odds ratio, 6.47), the investigators found.
Overall, nearly 40% of the myositis patients had autoantibodies, with anti–Jo-1 occurring most often and in similar frequency in both primary and overlap patients (in 18% and 19%, respectively). The presence of anti–Jo-1 was predominantly associated with polymyositis (in 84% of patients), vs. dermatomyositis, they noted.
Improving the classification of myositis patients using information about myositis-specific and -associated antibodies is important. Clinicians have to consider a variety of these overlap syndromes when treating myositis because the initial treatment provides the best chance of effectively controlling the disease and preventing long-term organ damage.
For example, the researchers found that interstitial lung disease, fever, arthritis, and mechanic's hand were all significantly positively associated with anti–Jo-1 autoantibody positivity in the patients in this study, and that anti–Jo-1 positivity was associated with a need for second-line treatment in primary myositis (OR, 1.95), but not in overlap disease (OR, 0.8).