TNF and Arthritis: Patients with CNO with associated PPP/psoriasis and/or arthritis demonstrated higher IL‐6 and IL‐8 levels than patients without extraskeletal features (mean difference 0.7 pg/mL [95% CI] 0.2–1.3, p = 0.02 and 2.1 pg/mL [95% CI] 0.03–4.2, p = 0.047, Fig. 4), but this was not the case for TNF‐α.