Background: There is little consensus regarding the prevalence and distribution of underlying systemic diseases among patients with pyoderma gangrenosum. Objective: The objective of this study was to synthesize existing data on the prevalence of associated systemic diseases in patients with pyoderma gangrenosum. Methods: We performed a systematic review and meta-analysis of observational studies in MEDLINE, EMBASE, and Scopus (1823–2017). The quality of evidence was assessed using a modified Newcastle–Ottawa Scale. A meta-analysis was performed using random-effects models to estimate pooled prevalence rates with 95% confidence intervals. Results: Twenty-one eligible studies comprising 2611 patients with pyoderma gangrenosum were included in the quantitative synthesis. The overall random-effects pooled prevalence of associated systemic diseases was 56.8% (95% confidence interval 45.5–67.4). The leading underlying disease was inflammatory bowel disease (17.6%; 95% confidence interval 13.0–22.7), followed by arthritis (12.8%; 95% confidence interval 9.2–16.9), hematological malignancies (8.9%; 95% confidence interval 6.5–11.6), and solid malignancies (7.4%; 95% confidence interval 5.8–9.1). In 16.3% (95% confidence interval 7.7–27.1) of cases, the onset of pyoderma gangrenosum was attributed to the pathergy phenomenon. Conclusions: More than half of patients with pyoderma gangrenosum present with a relevant underlying disease. Inflammatory bowel disease and arthritis are the most frequently associated diseases. Relative to the reported literature, the pooled prevalence of arthritis and hematological malignancies is lower, while the pooled prevalence of solid malignancies is higher. Owing to the high level of heterogeneity among most of the comparisons, results should be interpreted with caution.
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