Novel use of Siltuximab in a patient with VEXAS Syndrome.

VEXAS syndrome (vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic) is an increasingly recognized disorder that occurs due to somatic mutations of a ubiquitin-activating enzyme encoded by ubiquitin-like modifier activating enzyme 1 gene, UBA1. Clinical findings associated with VEXAS syndrome include recurrent fevers, polychondritis, periorbital edema, pleural effusions, myocarditis and/or pericarditis, hepatosplenomegaly, myelodysplastic syndrome, cytopenias, inflammatory arthritis, neutrophilic dermatosis, and deep venous thrombosis. Novel renal manifestations like interstitial nephritis are infrequent, and to our knowledge, acute renal failure due to C3 glomerulonephritis (C3GN) has not yet been reported. Overwhelming systemic inflammation can result in morbid end-organ damage and death. While there is no formal guideline or established protocol for its management, treatment of VEXAS syndrome with tocilizumab, an interleukin-6 (IL-6)-directed therapy, has been described in the literature. Here, we report a case of a 71-year-old male patient presenting with C3GN as an initial manifestation of VEXAS syndrome and explore the rationale for our approach to treatment with IL-6 blockade. Our patient was initially treated with two inpatient doses of tocilizumab with successful transition to siltuximab in the outpatient setting. He continues to benefit from ongoing siltuximab treatment for more than one year to date without any safety issues or relapse of VEXAS syndrome.