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The prevalence is unknown, but it is estimated to account for 1% of the systemic vasculitides.

Primary angiitis of the central nervous system (PACNS) usually affects middle-aged adults (mean age 51 years). Clinical presentation is variable, ranging from hyper acute to chronic and insidious, but typically has a progressive clinical evolution. The most common symptom is headache, variable in description but very rarely a thunderclap headache. Other symptoms include cognitive impairment (usually insidious), stroke (typically multiple, occurring over a (long) period and affecting different areas of the vascular bed) and transient ischemic attacks. Rarely, cranial nerve involvement, myelopathy, seizures or ataxia are observed. Associated angiographic abnormalities are common, cerebral MRI is almost invariably abnormal with nonspecific findings (including, rarely, solitary mass lesion), and cerebrospinal fluid (CSF) examination shows aseptic inflammatory abnormalities. Constitutional symptoms such as fever, weight loss and visceral organ involvement are rare and if present, should raise the suspicion of more systemic illnesses.

The primary defect is unknown. Pathological inflammation process affecting the small and medium-sized cerebral vessels causes them to become narrowed, occluded and thrombosed, leading to tissue ischemia and necrosis of the territories of the involved vessels.

Diagnosis of PACNS is established in a patient who: (i) has a history of unexplained neurologic deficit after thorough clinical and laboratory evaluation, (ii) has a documented (by cerebral angiography and/or tissue examination) of an arteritic process within the central nervous system, and (iii) no evidence of systemic vasculitis or any other condition to which the angiographic or pathological features could be secondary. Angiography abnormalities encountered in PACNS are characterized by irregular eccentric notched appearance with distal cutoffs and neovascularization, and typically asymmetric involvement. CSF findings resemble those of an aseptic meningitis with modest lymphocytic pleocytosis, normal glucose levels, elevated protein levels and, occasionally, the presence of oligoclonal bands and elevated IgG synthesis.

Differential diagnosis of PACNS is extensive and challenging, and comprises a range of systemic inflammatory conditions, infections, conditions with cerebral angiographic abnormalities (in particular, reversible vasoconstriction syndrome (RCVS) has highly similar clinical presentation; however, the associated headache is predominantly thunderclap by quality), and other neoplastic, genetic or neurological conditions.

Glucocorticoids combined with immunosuppressive agents, i.e. cyclophosphamide, has been successful in most cases. Accompanying prophylaxis for P. jirovecii and osteoporosis is necessary.

The disease is chronic and relapses are not uncommon.

Last update: October 2020 - Expert reviewer(s): Pr Xavier PUECHAL - Pr Benjamin TERRIER