Background.Recent epidemiologic studies have shown an association between psoriasis, psoriatic arthritis (PsA) and inflammatory bowel diseases (IBD). Recently, measurement of fecal calprotectin (FC) demonstrated a good sensitivity and specificity for intestinal inflammation.

Primary objective of present study was to evaluate the presence of occult bowel inflammation in patients with PsA as expressed by elevated levels of FC. Secondary objectives were to investigate the correlation between the levels FC and clinical and laboratory features, and the outcome of CF-positive patients in terms of IBD development.

A number of studies evaluated the presence of occult intestinal inflammation by using FC assay in patients with axial SpA. In 2000, a study conducted in PsA patients without bowel symptoms showed at mucosa biopsies the presence of microscopic changes, increase in lamina propria cellularity, consisting of plasma cells and lymphocytes, and lymphoid aggregates.Present prospective case-control study was designed to investigate occult intestinal inflammation by using FC assay in consecutive patients with PsA at onset, and who had no abdominal symptoms. Five Italian Centers contributed to patients recruitment adopting the same inclusion and exclusion criteria over a 3 year period.

FC levels were measured at baseline with Bühlmann fCAL Turbo, Switzerland® kit. This automated method is a particle enhanced turbidimetric immunoassay employing polyclonal antibodies. The manufacturer cut-off for FC positivity was 50 μg/g, with a sensitivity of 100% and a specificity of 53.1%.

The number of patients developing IBD was evaluated at the end of follow-up. Clinical and laboratory data collection was centralized and two experts statisticians performed the data analysis.

Statistical analysis. All demographic, clinical, and laboratory data were collected and descriptive statistics, presented as mean value and standard deviation, were calculated using Microsoft ® Office Excel for Windows and ©2019 Minitabs, LLC for Windows. Chi-square test was used for categorical variables. FC test sensitivity, specificity, positive (PPV) and negative (NPV) predictive values were calculated. Bayes's theorem was used to calculate the 95% confidence interval (95%CI). Correlations were calculated using Spearman's correlation (rs). P values ≤ 0.05 were accepted as statistically significant.

The median follow-up was 30 months.

Inclusion Criteria:

• age >18 years
• absence of any abdominal symptoms or diarrhoea
• non-steroidal anti-inflammatory drug (NSAIDs) interruption 10 days before enrollment
• Corticosteroids (CS) at stable low dose (prednisone 10 mg/day or equivalent) during the preceding 2 weeks were permitted in both groups.

Exclusion Criteria:

• age < 18 years
• previous diagnosis of CD or UC or current diagnosis of infectious colitis
• previous therapy with traditional DMARDs or any biologic therapies
• CS at high doses.

Both cases and controls were abdominal symptom-free.