Recurrent Severe Drug‐Induced Aseptic Meningitis due to Trimethoprim–Sulfamethoxazole Mimicking Ventriculitis‐Like MRI Findings in a Patient Receiving Anti–PD‐1 Therapy

ABSTRACT Drug‐induced aseptic meningitis is a rare and usually self‐limiting condition. Although clinical and cerebrospinal fluid findings may resemble those of bacterial meningitis, brain magnetic resonance imaging findings are typically normal. An 80‐year‐old woman receiving anti–PD‐1 antibody therapy for bladder cancer developed severe meningitis with high fever and disturbed consciousness. Brain magnetic resonance imaging revealed findings suggestive of ventriculitis, strongly suggesting bacterial meningitis; however, blood and cerebrospinal fluid cultures obtained before the initiation of antibiotic therapy were negative. Two months earlier, the patient had experienced a similar episode of severe meningitis of unknown etiology. Careful review of the clinical course revealed that trimethoprim‐sulfamethoxazole had been administered shortly before the onset of both episodes. The patient was diagnosed with recurrent drug‐induced aseptic meningitis caused by trimethoprim‐sulfamethoxazole. Patients with drug‐induced aseptic meningitis rarely present with severe clinical and radiological features mimicking bacterial meningitis. Therefore, it should be considered in patients with culture‐negative meningitis, particularly those receiving immune checkpoint inhibitors.