Primary angiitis of the central nervous system: avoiding misdiagnosis and missed diagnosis of a rare disease.

Primary angiitis of the central nervous system (PACNS) is an extremely rare condition, defined as a vasculitis limited to the CNS with no identifiable cause. Its presentation is non-specific and includes headache, cognitive dysfunction and focal neurological signs. Laboratory studies, neuroimaging and angiography are neither sufficiently sensitive nor specific for diagnosis; a definitive diagnosis requires brain biopsy. As a result, PACNS is commonly misdiagnosed. Here, we review its clinical, laboratory and radiological features, and focus on avoiding common diagnostic pitfalls.