title: Undifferentiated spondyloarthritis vs ankylosing spondylitis and psoriatic arthritis: a real-life prospective cohort study of clinical presentation and response to treatment.
abstract: OBJECTIVE
  SpA is a phenotypically heterogeneous disease, with AS and PsA as its best studied subtypes. This study aimed to investigate whether, despite a different phenotypic presentation, patients with undifferentiated SpA (uSpA) have similar disease activity and response to treatment to those with AS and PsA.
  
  
  METHODS
  175 patients presenting at a dedicated SpA outpatient clinic were recruited in a real-life prospective cohort with follow-up every 3 months. Clinical characteristics, disease activity at presentation and response to treatment of uSpA were compared with AS and PsA.
  
  
  RESULTS
  Twenty-three per cent (n = 40) of the patients were classified as uSpA. These patients were younger and tended to have a shorter disease duration than AS and PsA patients. uSpA patients exhibited a mixed axial (inflammatory back pain in 87.5%) and peripheral (peripheral arthritis in 62.5%) phenotype, with almost half of the patients having low-grade sacroiliitis on conventional X-ray. The overall disease activity in uSpA was similar to AS and higher than in PsA, also when analysing only anti-TNF naive patients. Initiation of TNF blockade significantly decreased disease activity in uSpA, with a similar amplitude to that in AS and PsA.
  
  
  CONCLUSIONS
  uSpA is a frequent, severe and anti-TNF-responsive phenotypic subtype of SpA. In agreement with the new ASAS classification criteria for axial and peripheral SpA and emerging data on TNF blockade in non-radiographic axial SpA and peripheral uSpA, these data emphasize the need for early diagnosis and optimal treatment of not only AS and PsA but also other SpA subforms.
authors.affiliation: Academic Medical Center/University of Amsterdam, Department of Clinical Immunology and Rheumatology, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands. d.l.baeten@amc.uva.nl.
authors.forename: Jacqueline E
authors.initials: JE
authors.lastname: Paramarta
authors.forename: Leen
authors.initials: L
authors.lastname: De Rycke
authors.forename: Carmen A
authors.initials: CA
authors.lastname: Ambarus
authors.forename: Paul P
authors.initials: PP
authors.lastname: Tak
authors.forename: Dominique
authors.initials: D
authors.lastname: Baeten
mesh_terms: D000328:Adult; D000367:Age Factors; D017668:Age of Onset; D018501:Antirheumatic Agents / Q000627:therapeutic use; D015535:Arthritis, Psoriatic / Q000175:diagnosis / Q000188:drug therapy; D005260:Female; D005938:Glucocorticoids / Q000627:therapeutic use; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012720:Severity of Illness Index; D025241:Spondylarthritis / Q000175:diagnosis* / Q000188:drug therapy; D013167:Spondylitis, Ankylosing / Q000175:diagnosis / Q000188:drug therapy; D016896:Treatment Outcome; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors
chemical_list: D018501:Antirheumatic Agents; D005938:Glucocorticoids; D014409:Tumor Necrosis Factor-alpha
keywords: ankylosing spondylitis; anti-TNF treatment; psoriatic arthritis; spondyloarthritis; undifferentiatied spondyloarthritis