Seronegative spondyloarthropathies: to lump or split?

The advent of novel biological therapies for the treatment of rheumatic disease has renewed interest in the seronegative spondyloarthropathies (SpAs). International efforts are redefining disease classification and measures of disease activity, outcome, metrology, and imaging. However, opinion is divided between those who propose that the SpA group represents the same disease with variable expression (the "lumpers") and those who consider these to be separate diseases with shared clinical features (the "splitters"). This review presents the evidence for both approaches.