Rare (incidence 2/million)
Many symptoms / lab findings possible:- Raynaud’s phenomenon common
- ANA ↑
- No renal or CNS involvement
- Arthritis worse
- SLE Antibodies negative
- MCTD Antibody: Anti-U1 RNP
Invariably Dx’d by rheumatology during W/U for atypical SLE
See posting Polyarthralgias.