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Definitions of response and remission for the Robarts Histopathology Index
  1. Rish K Pai1,
  2. Reena Khanna2,3,
  3. Geert R D’Haens2,4,
  4. William J Sandborn2,5,
  5. Jenny Jeyarajah2,
  6. Brian G Feagan2,
  7. Niels Vande Casteele2,6,
  8. Vipul Jairath2,3,7
  1. 1Department of Pathology and Laboratory Medicine, Mayo Clinic Arizona, Scottsdale, Arizona, USA
  2. 2Robarts Clinical Trials, London, Ontario, Canada
  3. 3Department of Medicine, University of Western Ontario, London, Ontario, Canada
  4. 4Academic Medical Center, University of Amsterdam, Amsterdam, Netherlands
  5. 5Division of Gastroenterology, University of California, San Diego, California, USA
  6. 6Department of Medicine, University of California, San Diego, California, USA
  7. 7Department of Epidemiology and Biostatistics, University of Western Ontario, London, Ontario, Canada
  1. Correspondence to Dr. Rish K Pai, Department of Laboratory Medicine and Pathology, Mayo Clinic, Scottsdale, Arizona 85259, USA; pai.rish{at}mayo.edu

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The Robarts Histopathology Index (RHI) is a recently validated instrument that measures histological disease activity in ulcerative colitis.1 Given the increasing importance and use of histology in UC as a treatment outcome, additional evaluation and clarification of the definitions for histological remission and response using the RHI is needed.

During the development of the RHI, we demonstrated that most patients in clinical or endoscopic remission had an RHI≤6. However, an RHI≤6 should not be used to define histological remission as was recently suggested by Magro et al.2 Rather, the minimal criteria for histological remission should be the absence of neutrophils from the mucosa (both lamina propria and epithelium), as neutrophils have long been used to define histologically active disease.3 Furthermore, the presence of mucosal neutrophils in biopsies from patients in clinical remission predicts clinical relapse.4 Using the RHI, an absence of mucosal neutrophils is defined as RHI≤3 with the additional requirement of subscores of 0 for lamina propria neutrophils and 0 for neutrophils in epithelium. Given that basal plasmacytosis has also been suggested as an important histological predictor of adverse outcomes,5 an alternate histological endpoint that requires both the absence of mucosal neutrophils and basal plasmacytosis defined as an RHI≤1 could be attractive. However, this composite definition might be too …

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