This chapter deals with isolated angiitis of the central nervous system (CNS), and begins with an overview of the pathology and pathogenesis of the condition. The nonspecific pathological pattern of isolated CNS angiitis is characterized by infiltrations of the vascular walls with mononuclear cells including lymphocytes, macrophages, and histiocytes. The pathogenesis of isolated CNS angiitis is unknown and progress is slow because of the rarity of tissue samples acquired from carefully documented cases. Brain imaging, angiography, and brain biopsy are the diagnostic options investigated in the chapter. In patients with a unique focal presentation such as stroke, and with isolated CNS angiitis suspected on the basis of angiography alone, a course of several-weeks of high-dose corticosteroids associated with a calcium channel blocker and no immunosuppressor can be proposed. The diagnosis of reversible cerebral angiopathy should be carefully considered in these patients.

Lyme disease, the multisystem infectious disease caused by the tick-borne spirochete Borrelia burgdorferi, readily invades the central nervous system (CNS) and, in up to 15% of patients, causes symptomatic meningitis or involvement of the cranial or spinal nerves. The clinical evidence supporting an association between B. burgdorferi infection and cerebral vasculitis or stroke is tenuous at best. Unfortunately, parenchymal brain disease has not been reported in any animal model. Peripheral nerve disease occurs fairly commonly both in infected patients and in experimentally infected rhesus macaque monkeys. Although in both humans and monkeys this is a patchy multifocal disease (mononeuritis multiplex), with perivascular inflammatory infiltrates evident in biopsied nerves, in neither has there ever been evidence of a true vasculitis or significant vasculopathy. Thus, although neurosyphilis has been known for many years to cause vascular inflammation and damage, to date there is little proof that this occurs in Lyme disease.