title: New-onset polyarthritis during successful treatment of hidradenitis suppurativa with infliximab.
abstract: BACKGROUND
  Hidradenitis suppurativa (HS) can be associated with several forms of arthritis, usually considered as reactive arthritis. A new observation is that some patients with HS develop arthritis after treatment with infliximab (antitumour necrosis factor-α).
  
  
  OBJECTIVE
  A retrospective study was performed to establish the frequency and clinical presentation of new-onset arthritis during infliximab treatment.
  
  
  METHODS
  Between 2005 and 2009, 27 individuals with severe HS were treated with infliximab and followed up closely. Laboratory parameters and side-effects were recorded. The frequency of arthritis was compared with control groups consisting of 227 patients with HS not treated with any biological, 22 patients with HS treated with adalimumab and 28 patients with psoriasis treated with infliximab, in the same period at the same clinic.
  
  
  RESULTS
  Five of the 27 patients with HS (18%) treated with infliximab developed an acute and painful polyarthritis during treatment. The arthritis occurred on average after 12 months of treatment, was not clearly associated with anti-infliximab antibodies and resolved on average after 4 months. Interestingly, none of the patients had suffered from arthritis before despite the long duration of HS and all showed a good skin response to infliximab. Moreover, arthritis was not observed in any of the control groups. Compared with the adalimumab group and the psoriasis group, odds ratios of 7·241 [95% confidence interval (CI) 1·15-45·6] and 9·025 (95% CI 1·45-55·82) were calculated.
  
  
  CONCLUSIONS
  The five cases described in this article suggest that infliximab treatment in HS can induce a transient but severe polyarthritis. The underlying mechanisms remain to be investigated further.
authors.affiliation: Department of Dermatology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands. d.c.vanrappard@amc.uva.nl
authors.forename: D C
authors.initials: DC
authors.lastname: van Rappard
authors.forename: J E
authors.initials: JE
authors.lastname: Mooij
authors.forename: D L P
authors.initials: DL
authors.lastname: Baeten
authors.forename: J R
authors.initials: JR
authors.lastname: Mekkes
mesh_terms: D000328:Adult; D000893:Anti-Inflammatory Agents / Q000009:adverse effects*; D000911:Antibodies, Monoclonal / Q000009:adverse effects*; D001168:Arthritis / Q000139:chemically induced*; D005260:Female; D017497:Hidradenitis Suppurativa / Q000188:drug therapy*; D006801:Humans; D000069285:Infliximab; D008297:Male; D008875:Middle Aged; D009426:Netherlands; D010641:Phenotype; D012189:Retrospective Studies; D016896:Treatment Outcome
chemical_list: D000893:Anti-Inflammatory Agents; D000911:Antibodies, Monoclonal; D000069285:Infliximab