To determine whether studying patients with strictly unilateral relapsing primary angiitis of the central nervous system (UR-PACNS) can support hemispheric differences in immune response mechanisms, we reviewed characteristics of a group of such patients.  

UR-PACNS is rarely described. This disease subtype may hold clues to some immunological properties of the brain.

We surveilled our institution for UR-PACNS patients. We defined UR-PACNS as biopsy-proven PACNS relapsing strictly in one brain hemisphere three or more times, with or without hemi-atrophy. Three total cases were identified at our institution. A literature search for similar cases yielded four additional cases. The combined 7 cases were reviewed for demographic, clinical, imaging and pathological trends.  

The median age at time of clinical onset among the 7 cases was 26 years [range 10-49 years]; 5 were male (71%). All seven patients presented with seizures. The mean follow-up duration was 7.5 years [4-14.1 years]. The annual relapse rate ranged between 0.2 and 1. UR-PACNS involved the left cerebral hemisphere in 5 of the 7 patients. There was no consistent relationship between the patient’s dominant hand and the diseased side. When performed (5 cases), conventional angiogram was non-diagnostic. Cerebrospinal fluid examination showed nucleated cells and protein levels in normal range in 3 cases, and ranged from 6 to 11cells/µL and 49 to 110mg/dL in 4 cases. All cases were diagnosed with lesional biopsy, showing lymphocytic type of vasculitis of the small and medium-sized vessels. Patients treated with steroids alone showed progression.

We hypothesize that a functional difference in immune responses; caused by such discrepancies as basal levels of cytokines, asymmetric distribution of microglia, and differences in modulation of the systemic immune functions; rather than a structural antigenic difference, between the right and left brain may explain this phenomenon, but this is speculative.