Vasculitisis inflammation of the blood vessels, which may involve either the central nervous system (CNS), or the peripheral nervous system (PNS), or both. This involvement may be primary and restricted to the CNS, and rarely to the PNS. "Primary angiitis of the CNS" is the term used to describe isolated CNS involvement by vasculitis, in which neither the clinical presentation and behaviour of the disease, nor the histopathology is uniform. This heterogeneity indicates a spectrum, depending on the type and extent of the vascular involvement seen within the CNS, covering a group of disorders, rather than a single disease. This may explain the different prognosis and response to treatments.. In clinical practice vasculitis of the nervous system, secondary to a known cause or underlying disease is more commonly seen than as a primary disorder. Primary systemic vasculitides and connective-tissue disorders, Behcet's Disease, lymphoproliferative diseases and other malignancies, some infections and related conditions, drugs and substance abuse are some of the conditions known to cause vasculitis in the nervous system. There is a broad variety of pathogenetic mechanisms. Both the CNS and the PNS maybe involved, either separately or together.