IMPORTANCE Pyoderma gangrenosum is an inflammatory neutrophilic dermatosis. Current knowledge of this rare disease is limited owing to a lack of validated diagnostic criteria and large population studies. OBJECTIVE To evaluate the association of age with the clinical presentation and comorbidities of pyoderma gangrenosum. DESIGN, SETTING, AND PARTICIPANTS This was a multicenter retrospective cohort study performed at tertiary academic referral centers in urban settings. Adults (Ն18 years) who were evaluated and diagnosed as having pyoderma gangrenosum at the Brigham and Women's and Massachusetts General Hospitals from 2000 to 2015 and the University of Pennsylvania Health System from 2006 to 2016 were included. MAIN OUTCOMES AND MEASURES Patient demographics, clinical features, medical comorbidities, and treatment. RESULTS Of the 356 validated cases of pyoderma gangrenosum included in the study, 267 (75%) were women and 284 (84.8%) were white. The mean (SD) age at presentation was 51.6 (17.7) years. Pathergy was recorded in 100 patients (28.1%). A total of 238 patients (66.9%) had associated medical comorbidities: inflammatory bowel disease in 146 patients (41.0%); inflammatory arthritis in 73 patients (20.5%); solid organ malignant neoplasms in 23 patients (6.5%); hematologic malignant neoplasms in 21 patients (5.9%); and hematologic disorders, specifically monoclonal gammopathy of undetermined significance, myelodysplastic syndrome, and polycythemia vera in 17 patients (4.8%). When stratified by age, pathergy was more common in patients 65 years or older (36.3% vs 24.3%; P = .02). Inflammatory bowel disease was the only medical comorbidity that was more common in patients younger than 65 years (47.7% vs 26.6%; P < .001), while a number of medical comorbidities were more common in those 65 years or older, including rheumatoid arthritis (13.3% vs 6.2%; P = .03), ankylosing spondylitis (1.8% vs 0%; P = .04), solid organ malignant neoplasms (13.3% vs 3.3%; P < .001), hematologic malignant neoplasms (9.7% vs 4.1%; P = .04), and the aforementioned hematologic disorders (10.6% vs 2.1%; P < .001). CONCLUSIONS AND RELEVANCE Although clinical presentation in this large cohort was similar between different age groups, disease associations varied by age. The findings of this study may allow for a more focused, age-specific evaluation of patients with pyoderma gangrenosum.

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IMPORTANCE Necrobiotic xanthogranuloma (NXG) is a non-Langerhans cell histiocytosis classically associated with paraproteinemia attributable to plasma-cell dyscrasias or lymphoproliferative disorders. Despite the morbidity of NXG, the literature is limited to case reports and small studies, and diagnostic criteria are lacking.OBJECTIVE To evaluate the characteristics of NXG and propose diagnostic criteria. DESIGN, SETTING, AND PARTICIPANTSThis multicenter cross-sectional study was conducted at tertiary academic referral centers and followed by a systematic review and a consensus exercise. The multicenter cohort included patients with NXG diagnosed at the Brigham and Women's and Massachusetts General Hospitals (2000-2018), the University of Iowa Hospitals and Clinics (2000-2018), and the University of Pennsylvania Health System (2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018). The systematic review was conducted in 2018 and included patients with NXG identified in the Cochrane, Ovid EMBASE, PubMed, and Web of Science databases. The consensus exercise was conducted by 8 board-certified dermatologists to identify diagnostic criteria.MAIN OUTCOMES AND MEASURES Demographic factors, comorbidities, clinical features, and treatment response. RESULTSOf 235 included patients with NXG (34 from the multicenter cohort and 201 from the systematic review results), the mean (SD) age at presentation was 61.6 (14.2) years; 147 (62.6%) were female. Paraproteinemia was detected in 193 patients (82.1%), most often IgG-κ (117 patients [50.0%]). A malignant condition was detected in 59 patients (25.1%), most often multiple myeloma (33 patients [14.0%]). The overall rate of paraproteinemia and/or a malignant condition was 83.8% (197 patients). In the multicenter cohort, evolution of paraproteinemia into multiple myeloma was observed up to 5.7 years (median [range], 2.4 [0.1-5.7] years) after NXG presentation. Cutaneous lesions consisted of papules, plaques, and/or nodules, typically yellow or orange in color (113 of 187 [60.4%]) with a periorbital distribution (130 of 219 [59.3%]). The eye was the leading site of extracutaneous involvement (34 of 235 [14.5%]). In the multicenter cohort, intravenous immunoglobulin had the best treatment response rate (9 of 9 patients [100%]), followed by antimalarial drugs (4 of 5 patients [80%]), intralesional triamcinolone (6 of 8 patients [75%]), surgery (3 of 4 patients [75%]), chemotherapy (8 of 12 patients [67%]), and lenalidomide or thalidomide (5 of 8 patients [63%]). The consensus exercise yielded 2 major criteria, which were (1) clinical and (2) histopathological features consistent with NXG, and 2 minor criteria, consisting of (1) paraproteinemia, plasma-cell dyscrasia, and/or other associated lymphoproliferative disorder and (2) periorbital distribution of cutaneous lesions. In the absence of foreign body, infection, or another identifiable cause, fulfillment of both major and at least 1 minor criterion were proposed to establish the diagnosis of NXG.CONCLUSIONS AND RELEVAN...

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