Overlap Syndromes
Other overlap syndromes not associated with high-titer anti-U1-RNP antibodies are:
• SLE is associated with inflammatory myopathy in 4% to 16% of cases.
• SLE can be associated with RA (“RUPUS”) with positive rheumatoid factor, nodules, and erosive polyarthritis. This overlap is relatively uncommon, and the diagnosis should not be made simply because of a positive ANA in a patient with RA, nor in patients with lupus with an inflammatory arthritis but without rheumatoid factor/cyclic citrullinated peptide positivity and/or erosive disease.
• SSc can be associated with myositis. One specific overlap is characterized by antibody to PM-Scl, a complex of 16 polypeptides located at the site of ribosomal assembly in the nucleolus (hence patients with PM-Scl antibody commonly have a nucleolar pattern ANA on immunofluorescent antibody assay).
• Limited SSc can be associated with PBC. Limited SSc precedes PBC by an average of 14 years. Antimitochrondrial antibody can be seen in 18% to 27% of limited SSc patients. Many also have SS.
• SSc can be associated with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (perinuclear ANCA/anti-myeloperoxidase).
• Myositis overlap syndromes: antisynthetase antibody syndromes (: Idiopathic Inflammatory Myopathies).
• RA can overlap with SSc, SLE, MCTD, or SS. Patients with anti-RA-33 (hnRNP-A2) are most likely to develop an erosive arthritis.
