Researchers at Los Angeles Medical Center, and University of California, San Francisco determined the incidence and clinical features of pediatric multiple sclerosis (MS) and other forms of acquired demyelinating syndromes (ADS) in the multiethnic membership of Kaiser Permanente Southern California from Jan 1, 2004, to Dec 31, 2009. Using a combination of electronic database searches followed by complete medical records review, 81 incident cases of ADS were identified from 4.87 million person years of observation in children 0-18 years of age. Incidence rate of MS was 0.51/100,000 per person-years, and of other forms of ADS, 1.56/100,000. The ADS syndromes included optic neuritis, transverse myelitis, clinically isolated syndrome (CIS), and acute disseminated encephalomyelitis (ADEM). The overall incidence of ADS was 1.66/100,000 per person-years. Incidence of ADS was higher in black (4.4; p<0.001) and Asian/Pacific Islander (2.8; p=0.02) than white (1.03) and Hispanic (1.5) children. MS was significantly more frequent in black than in white children (p=0.001). Children with ADEM were significantly younger than those with other types of ADS (mean age 5.6 vs 14.6 years). 
COMMENT. In a population-based cohort of Southern Californian children, the incidence of acquired demyelinating syndromes is 1.66 per 100,000 person-years. The incidence of ADS and MS is higher in black compared with white and Hispanic children. Pediatric ADS is rare, a previous study in Canadian children finding an overall ADS incidence of 0.9 per 100,000. 
Risk of MS in children is dependent on genetic factors (presence of HLA-DRB1*15 genotype) and environmental triggers (previous infection with Epstein-Barr virus, and low serum 25-hydroxyvitamin D concentrations) . The increased risk conveyed by HLA-DRB1*15 alleles relates to chronic MS rather than ADS in general . Whereas remote infection with Ebstein-Barr virus is associated with an increased risk of pediatric MS, some viruses (cytomegalovirus) may lower MS susceptibility. HSV-1 remote infection does not increase odds of MS but it has a strong interaction with HLA-DRB1 in predicting MS.