The DIGICOD cohort: A hospital-based observational prospective cohort of patients with hand osteoarthritis - methodology and baseline characteristics of the population.

OBJECTIVE: Despite its prevalence, there are few worldwide hand osteoarthritis (HOA) cohorts. The main objective of DIGItal COhort Design (DIGICOD) cohort is to investigate prognostic clinical, biological, genetic and imaging factors of clinical worsening after 6years follow-up. METHODS: DIGICOD is a hospital-based prospective cohort including patients>35years-old with symptomatic HOA fulfilling: (i) ACR criteria for HOA with≥2 symptomatic joints among proximal/distal interphalangeal joints or 1st interphalangeal joint with Kellgren-Lawrence (KL)≥2; or (ii) symptomatic thumb base OA with KL≥2. Main exclusion criteria were inflammatory arthritis and crystal arthropathies. Annual clinical evaluations were scheduled with imaging (X-rays of the hands and of other OA symptomatic joints) and biological sampling every 3years. Hand radiographs are scored using KL and anatomical Verbruggen-Veys scores. Follow-up visits are ongoing. Cohort methodology and baseline characteristics are presented. RESULTS: Between April 2013 and June 2017, from the 436 HOA included patients, 426 have been analysed of whom 357 (84%) are women. Mean age±standard deviation was 66.7±7.3years and mean disease duration was 12.6±9.6years. Metabolic syndrome affected 151 (36.5%) patients. Mean Visual Analog Scale (VAS) hand pain (0-100mm) was 44.4±26.7mm at activity. Mean FIHOA (0-100) was 19.9±18.6. Elevated serum CRP level (≥5mg/L) involved 10% patients. Mean KL score (0-128) was 46.7±18 and the mean number of joint with KL≥2 was 15.1±6.3. Erosive HOA (defined as≥1 Erosive or Remodeling phase joint according to Verbruggen-Veys score) involved 195/426 (45.8%) patients and the median number (interquartile range) of erosive joints in erosive patients was 3.0 (1.0-5.0). CONCLUSION: DIGICOD is a unique prospective HOA cohort with a long-term 6years standardized assessment and has included severe radiologically HOA patients with a high prevalence of erosive disease.