Stevens-Johnson syndrome precipitating days after treatment for dostarlimab-induced autoimmune encephalitis: a case report.

Background: Immune checkpoint inhibitors (ICIs) are increasingly used in the first-line and maintenance treatment of advanced and recurrent endometrial cancer. Their expanding use has been accompanied by a rising incidence of immune-related adverse events (irAEs), which vary widely in presentation and severity. Severe neurologic and cutaneous irAEs are rare but can be life-threatening. Case presentation: A 69-year-old woman with FIGO stage IVB, mismatch repair-deficient endometrioid endometrial cancer receiving maintenance dostarlimab presented with altered mental status. When her encephalopathy persisted despite treatment of an identified infection and metabolic derangements and improved only with corticosteroids, she was diagnosed with presumed autoimmune encephalitis. Days later, approximately one to two weeks after receiving beta-lactam antibiotics and about five weeks after her last dostarlimab dose, she developed biopsy-confirmed Stevens-Johnson syndrome and toxic epidermal necrolysis (SJS/TEN), ultimately involving roughly 30% of her body surface area and requiring burn-center care. She recovered fully with no residual deficits. Conclusion: We propose that checkpoint inhibition, evidenced by the preceding neurologic irAE, primed the patient for a severe hypersensitivity reaction to a subsequently administered, ordinarily tolerated medication. This case underscores the importance of heightened vigilance for severe reactions to common drug exposures in patients with a recent irAE, even after immunotherapy has ended.