Supplementary tables.

<div><p>Background and aim</p><p>The involvement of mucosa associated lymphoid tissues (MALT) in the development of an autoimmune response in the skin is unclear and unstudied. In this study we sought to assess the relationship between removal of MALT tissues (MALTectomy) and the risk of development of psoriasis (overall or moderate-to-severe).</p><p>Methods</p><p>We conducted a prospective observational study based on E3N, a French cohort composed of 98 995 women born between 1925 and 1950 and insured by the health insurance of the national education system (MGEN). The study population included the 90 119 women that completed the 1990 baseline questionnaire with available information on MALTectomy and a valid incident diagnostic date for psoriasis. During the 1990–2018 follow-up period 2 433 incident cases of psoriasis were identified through self-reports while during the period for which drug reimbursement data were available from the MGEN database (2004–2018), 120 cases of moderate-to-severe psoriasis were identified. Hazard ratios (HR) and their 95% confidence intervals were estimated by Cox proportional hazards models and adjusted for known or putative psoriasis risk factors.</p><p>Results</p><p>Appendectomy was associated with an increased risk of psoriasis both in the univariate [HR: 1.17 (95% CI: 1.08–1.27)] and multivariable models [HR: 1.14 (95% CI: 1.05–1.24)]. A suggestive association with appendectomy was observed for moderate-to-severe psoriasis risk [univariate HR: 1.40 (95%CI: 0.97–2.02); multivariable HR: 1.36 (95%CI: 0.94–1.96)]. No association was observed between tonsillectomy or adenoidectomy both for overall and moderate-to-severe psoriasis.</p><p>Conclusions</p><p>The observed association between appendectomy and risk of psoriasis warrants further investigations as they may help to elucidate the disease etiology and improve risk prediction.</p></div>