Successful treatment of aneurysmal subarachnoid hemorrhage in polyarteritis nodosa with immunosuppressive therapy: illustrative case.

backgroundThe incidence of cerebral aneurysms in polyarteritis nodosa (PN) is low, and reports of subarachnoid hemorrhage (SAH) in patients with PN are even rarer. The necessity of head imaging may be underestimated, particularly when the patient is in remission. OBSERVATIONS: A 20-year-old female with PN, who had been in remission following anti-interleukin-6 receptor antibody therapy, developed SAH and was admitted to the authors' department. Cerebral angiography revealed multiple beaded changes in both carotid and vertebral arterial systems, along with several small aneurysms. These findings posed substantial difficulty in identifying the bleeding source and proceeding with surgical intervention. Therefore, the authors intensified the immunosuppressive therapy targeting the underlying PN. The patient remained free from rebleeding, her headaches and other symptoms resolved, and she was discharged in ambulatory condition. Follow-up MR angiography 3 months after discharge confirmed resolution of the small aneurysms. LESSONS: This case suggests that enhanced immunosuppressive therapy may be effective in treating both extracranial and intracranial vascular lesions in PN. In patients with PN, early and serial head imaging may be beneficial. The appearance of de novo aneurysms in the context of disease progression may indicate the need for more aggressive treatment. https://thejns.org/doi/10.3171/CASE25617.