When is brain biopsy useful/warranted as part of the diagnostic work-up in patients with suspected primary CNS angiitis?  

I have never diagnosed or seen a patient with primary angiitis of the CNS. First, I would ensure that the suspected diagnosis and findings are confined to the CNS and are not associated with a systemic inflammatory disease. If the condition is not confined to the CNS, other areas of the body may be ...

Rarely. As mentioned above, true PACNS is very rare (though I have seen one biopsy-confirmed case); a diagnosis of PACNS requires a biopsy. However, other non-inflammatory mimics are much more common, namely RCVS. This can be readily distinguished based on clinical grounds and thus spare a brain bio...

When suspecting PACNS, the workup should include an LP, vessel wall imaging, and a retina exam. If all results are negative, it's essential to consider other conditions on the differential diagnosis as well. We should have a low threshold for biopsy. Progressive white matter disease, progressive de...