Clinical significance of rare serum autoantibodies in rheumatic diseases: a systematic literature review
The identification of serum autoantibodies is central in the diagnosis of systemic autoimmune rheumatic disease (SARD), and an increasing number of specificities have been detected in the past years. This allows an early diagnosis in the active phases of diseases, with the identification of specific disease subsets that may ultimately improve the disease outcomes. Thanks to the use of old and new laboratory techniques that are becoming increasingly available worldwide, the number of rheumatic patients with a specific autoantibody is increasing and this is improving also our knowledge of disease trigger mechanisms. The paradigmatic example is the plethora of serum autoantibodies described in polymyositis and dermatomyositis, coined myositis-specific antibodies (MSA) which include antibodies directed against tRNA synthetases, anti-SRP, anti-Mi-2, and anti-TIF-1γ and can discriminate disease subtypes, particularly when associated with the risk of cancer. As a further example, anti-HMGCR antibodies have been reported in several studies in association with necrotizing autoimmune myositis that may follow statin use. To clarify the current knowledge on these rare specificities, we performed a systematic literature review. We focused on the main features associated to specific autoantibodies that are rarely identified in rheumatic disease, to increase the awareness and scientific knowledge on these autoantibodies in different ethnic groups worldwide.