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The authors conducted a population-based case-control study to investigate whether clinically observed chickenpox, linked with a level of intensity for clinical expression, increases the risk of multiple sclerosis (MS) in childhood. The cases were MS patients whose disease onset occurred between 1994 and 2003, before age 16 years, in France. Each case was matched for age, sex, and geographic origin with as many as 12 controls randomly selected from the general population. Information about clinically observed chickenpox in cases and controls before the index date regarding onset of MS was collected with a standardized questionnaire and was checked against health certificates. Conditional logistic regression was used to estimate the odds ratio for an association between MS and chickenpox. The 137 MS cases were matched with 1,061 controls. Clinically observed chickenpox had occurred in 76.6% of the cases and 84.9% of their matched controls. The adjusted odds ratio of MS onset associated with chickenpox occurrence was 0.58 (95% confidence interval: 0.36, 0.92). The authors concluded that clinically observed chickenpox was associated with a lower risk of childhood-onset MS in a French population.

The possibility of a link between active smoking and incident multiple sclerosis (MS) has been raised. However, possible links between incidence of MS and passive smoking, particularly in children, have not been analysed. We conducted a population-based, case-control study. The cases were patients with incident MS occurring between 1994 and 2003, before the age of 16 years, in France. Each case was matched for age, sex and geographic origin with 12 controls, randomly selected from the French general population. Information about the smoking history of the parents of the cases and controls was collected with a standardized questionnaire. Conditional logistic regression was used to estimate the rate ratio (RR) of MS associated with parental smoking at home. The 129 cases of MS were matched with 1038 controls. Information about parental smoking was obtained for all these cases and controls. Exposure to parental smoking was noted in 62.0% of cases and 45.1% of controls. The adjusted RR of a first episode of MS associated with exposure to parental smoking at home was 2.12 (95% confidence interval: 1.43-3.15). Stratification for age showed that this increase in risk was significantly associated with the longer duration of exposure in older cases (over 10 years of age at the time of the index episode)-RR 2.49 (1.53-4.08)-than in younger cases. Children exposed to parent smoking have a higher MS risk. The duration of exposure also affects the level of risk.

Public concern about possible increases in the risk of multiple sclerosis associated with hepatitis B vaccination has led to low vaccination coverage. We investigated whether this vaccination after a first episode of acute CNS inflammatory demyelination in childhood increased the risk of conversion to multiple sclerosis. We studied the French Kid Sclérose en Plaques (KIDSEP) neuropaediatric cohort of patients enrolled between 1994 and 2003 from their first episode of acute CNS inflammatory demyelination (inclusion in the cohort) until the occurrence of a second episode, up to 2005. A Cox proportional hazards model of time-dependent vaccine exposure was used to evaluate the effect of vaccination (hepatitis B, tetanus) during follow-up on the risk of second episode occurrence (conversion to multiple sclerosis). The cohort included 356 subjects with a mean follow-up of 5.8 years (SD 2.7). Relapse occurred in 146 (41%) subjects during follow-up; 33 subjects were exposed to hepatitis B vaccine and 28 to tetanus vaccine at some time during follow-up. The adjusted hazard ratio (HR) for relapse occurring within 3 years of hepatitis B vaccination was 0.78 (0.32-1.89) and during any time period was 1.09 (0.53-2.24). The adjusted HR for relapse occurring within 3 years of tetanus vaccination was 0.99 (0.58-1.67) and during any time period was 1.08 (0.63-1.83). We conclude that vaccination against hepatitis B or tetanus after a first episode of CNS inflammatory demyelination in childhood does not appear to increase the risk of conversion to multiple sclerosis, although the possibility of a small increase in risk cannot be excluded.

The prognostic factors for relapse of the initial MRI findings after a first episode of acute CNS inflammatory demyelination are unclear in children. In this study we aimed to identify initial MRI factors that are predictive of a second attack and disability after a first episode of acute CNS inflammatory demyelination in childhood. A cohort of 116 children who had a first episode of acute CNS inflammatory demyelination between 1990 and 2002 was studied using survival analysis methods. The initial MRI data were reviewed in a systematic, standardized, double-blind manner. The average follow-up was 4.9 +/- 3 years. Multivariate analysis showed that the rate of second attack was higher in patients with corpus callosum long axis perpendicular lesions (34 out of 116 patients, 30%) on the initial MRI [hazard ratio (HR) 2.89; 95% confidence interval (CI) 1.65-5.06] and/or with the sole presence of well-defined lesions (46 out of 116 patients, 40%) (HR 1.71; 95% CI 1.29-2.27). Both criteria were more specific predictors (100%) of relapse, demonstrating conversion to multiple sclerosis, than the three Barkhof criteria (63%), but were less sensitive (21% compared with 52%). None of the MRI criteria was predictive of severe disability. Using initial MRI and survival analysis methods, we identified two specific predictors of relapse and conversion to multiple sclerosis after a first episode of acute CNS inflammatory demyelination in childhood. Their low sensitivity, however, shows that this prediction remains difficult.