Objective: Hemophagocytic lymphohistiocytosis (HLH) is a rare potentially fatal multisystem inflammatory condition that is often triggered by an underlying medical condition. Epidemiologic data of HLH in adults with rheumatologic diseases are limited. The aim of our study was to characterize HLH hospitalizations in the US adult population with a special focus on patients with concomitant rheumatologic diseases. Methods:We conducted a medical records review of hospitalizations in the United States during 2016 and 2017 with a diagnosis of HLH. Hospitalizations were selected from the National Inpatient Sample. International Classification of Diseases, Tenth Revision codes were used to identify rheumatologic diseases. A multivariate logistic regression analysis was used to calculate adjusted odds ratios (OR adj ) for the association of HLH and rheumatologic diseases.Results: Seven hundred fifty hospitalizations had a principal billing diagnosis of HLH. The median age of our study population was 47.5 years, and males made up 55% of the population. Overall mortality was 17%, and the median length of stay was 12 days. Twenty-five percent of the HLH cases had a concomitant rheumatologic diagnosis. Multivariate logistic regression analysis showed systemic lupus erythematosus (SLE) with nephritis (OR adj , 5.7), SLE without nephritis (OR adj , 9.2), adult-onset Still disease (OR adj , 338.9), and ankylosing spondylitis (OR adj , 10.7) were significantly associated with HLH.Conclusions: This analysis represents the largest sample to date to assess HLH hospitalizations. Our study showed that SLE, adult-onset Still disease, and ankylosing spondylitis were strongly associated with HLH.

Granulomatosis with polyangiitis (GPA) and rheumatoid arthritis (RA) have shared features including vasculitis, ocular inflammation, interstitial lung disease, and arthritis but existing evidence indicates they are distinct conditions. Interestingly, the co-existence of GPA and RA has been described in the literature. Herein, we report two cases of GPA developing in patients with underlying RA and examine the relationship between the two conditions. Two cases of GPA that developed in patients with preexisting RA are described in detail. Additionally, PubMed was searched for articles in English showing an association of RA and GPA using keywords “rheumatoid arthritis, and vasculitis, and Wegener’s, and ANCA, and granulomatosis polyangiitis.” In addition to our two cases of RA and GPA overlap, 14 reports were identified in PubMed library from 1970 to 2020. Most of the cases were females (14/16, 88%), and had RA as the initial diagnosis (15/16, 94%). The mean age of RA diagnosis was 45.5 years, the mean age of GPA diagnosis was 52 years and the mean interval between both diagnoses was 101 months. Cyclophosphamide and steroid therapy were used in most of the cases. There are numerous reports of GPA and RA overlap in the literature. GPA should be considered in the differential diagnosis when vasculitis develops in patients with RA.

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