Polyarteritis Nodosa (PAN)
PAN usually presents in the fourth or fifth decade but can present in childhood. Men are affected twice as commonly as women. There can be an association with hepatitis B or C infection . There is typically multi-organ involvement. The systemic inflammatory process can be reflected in systemic signs such as fever, malaise, and weight loss. This can be supported by an elevated ESR, and renal involvement is usually accompanied by proteinuria as well as hypertension. Dermatological manifestations and peripheral neuropathy tend to be particularly common.
Despite potentially devastating effects, PAN is not uncommonly associated with CNS vascular involvement. In one report, 12% of 26 patients had only CNS involvement, while 34% had combined CNS and peripheral nervous system (PNS) involvement . This systemic vasculitis is associated with necrotizing inflammatory vascular lesions of primarily small- and medium-size muscular arteries. There tends to be preferential involvement of vessel bifurcations. There is microaneurysm formation with the potential for hemorrhage as well as thrombosis with infarction . Cumulative involvement of the brain can result in a multifocal encephalopathy in up to 40% of affected patients , but isolated cerebral infarction or hemorrhage can be the presenting manifestation. One can see a lacunar-type infarction pattern related to thrombotic microangiopathy . Generally speaking, in light of the potential for smaller vessel involvement, cerebral arteriography is recommended for evaluation of patients suspected of having the disease.
Diagnosis and Treatment
The spectrum of manifestation of a systemic vascular inflammatory process should raise suspicion for PAN in the differential diagnosis. Pathological confirmation is most readily determined when there is associated dermatological or PNS involvement available for biopsy. The diagnostic challenge of CNS involvement is lessened by the tendency for cerebral, or spinal, vasculitis to develop 2-3 years later than other manifestations.
The treatment is immunosuppression. In uncomplicated disease, corticosteroids can have a very positive impact on prognosis including survival . In more aggressive disease, cyclophosphamide combined with steroid can have a positive impact . Anecdotally, rituximab may provide benefit in refractory cases of PAN . Antiviral therapy combined with immunosuppression is reported to be of particular benefit in hepatitis B- and C-related PAN  especially in severe disease .