How Rare is CNS Vasculitis?
Primary CNS vasculitis is extremely rare, occurring at a rate of 2.4 cases per 1 million person-years. 1
Epidemiologic Data
The incidence of primary angiitis of the central nervous system (PACNS) is 2.4 cases per 1 million person-years, making it an exceptionally uncommon disorder. 1
The mean age of onset is approximately 50 years, with a male-to-female ratio of 2:1 (men affected twice as often as women). 2
This condition is so rare that most patients initially suspected of having PACNS ultimately receive an alternative diagnosis. 2
Clinical Context of Rarity
The extreme rarity of primary CNS vasculitis creates significant diagnostic challenges, as maintaining clinical expertise is difficult when the condition is encountered so infrequently. 3
Because of its rarity and non-specific presentation, PACNS is commonly misdiagnosed, with many mimicking conditions (reversible cerebral vasoconstriction syndrome, atherosclerosis, infections, malignancies) being far more common. 4, 3
The rarity is further compounded by the fact that CNS vasculitis can also occur secondary to systemic vasculitis or autoimmune diseases, making true primary CNS vasculitis even less common than the overall category of CNS vasculitis. 5
Implications of Rarity for Diagnosis
Given the extremely low incidence, patients with suspected primary CNS vasculitis should be managed in collaboration with centers of expertise where sufficient experience exists to navigate the complex differential diagnosis. 3, 6
The rarity means that no single laboratory test or imaging finding can reliably diagnose this condition, and clinicians must maintain a high index of suspicion while simultaneously considering more common alternative diagnoses. 5, 2
Brain biopsy remains the gold standard for definitive diagnosis, but even this has limitations due to the focal, patchy nature of the disease, with diagnostic yield around 70% even under optimal conditions. 3, 1