How do you approach treatment of suspected CNS vasculitis with a negative work up?

Suspected CNS vasculitis is, simply put, extremely challenging, most often because the diagnosis is difficult to make. Commonly, the diagnosis is suspected based upon non-invasive imaging showing an unusual distribution of infarcts and/or evidence of intracranial arteriopathy (CTA or formal DSA). I favour initially considering that the patient has some kind of vasculopathy and not leaping to the diagnosis of vasculitis. It is uncommon (but not impossible) that primary systemic vasculitides will ...

I'm curious to learn in this case what a negative workup entails and why a suspicion for CNS vasculitis is present or still exists with a negative evaluation. If I have learned anything from attending multiple lectures on CNS vasculitis and spending time with the vasculitis team at CCF, a biopsy is key for diagnosis, and I wouldn't treat without it.

I would approach this by evaluating other vasculopathies and by taking a multidisciplinary approach with my neuroimmunology and rheumatology colleagues for completion of workup (including brain/leptomeningeal biopsy if other work up negative with clinically high suspicion). If no other cause despite that and no contraindication with high clinical suspicion (despite an overall negative workup including a biopsy), then potentially giving a trial of empirical steroids (again this is in cases where ...