Idiopathic granulomatous angiitis of the CNS manifesting as diffuse white matter disease.

A 48-year-old man presented with progressive spastic paraparesis and diffuse white matter involvement on neuroimaging that suggested a primary demyelinating disease. Brain biopsy 3 years after onset of symptoms demonstrated idiopathic granulomatous angiitis. In patients with MRI features of diffuse white matter disease of uncertain etiology, open brain biopsy of leptomeninges and parenchyma should be considered to exclude idiopathic granulomatous angiitis of the CNS.