A 67-year-old man with no significant past medical history presented with a sudden onset of a severe headache, described as the worst of his life. Initial imaging revealed a diffuse subarachnoid hemorrhage with significant vasculopathy. Cerebral angiography showed dysplasia in the posterior cerebral arteries (PCAs), more pronounced on the left, without evidence of flow limitation, consistent with vasculitis.
The patient had a history of substantial outdoor activity, including chopping wood and painting barns, and a prior episode of Lyme disease treated approximately 7–8 years earlier. Cerebrospinal fluid (CSF) analysis revealed an elevated Lyme index, suggestive of CNS Lyme disease. Follow-up CT angiography of the head and neck showed moderate irregularity and a beaded appearance in the bilateral proximal-to-mid PCAs. Despite these findings, a comprehensive rheumatological workup was negative.
Given the patient's clinical history, imaging findings, and significant outdoor exposure, CNS vasculitis secondary to Lyme disease was strongly considered as the underlying cause of his subarachnoid hemorrhage.