Infection and Epilepsy: Current Dilemma.

Sir,

We read with interest the article titled “Prevalence of epilepsy and its association with exposure to Toxocara canis: A community-based, case–control study from rural Northern India”.[1] While the original article by Modi et al.[1] is commendable for the population-based study design, the results need to be seen in the light of another recent published meta-analysis[2] on the same topic which leaves us indecisive. It also throws open several questions which have the potential to be addressed in a similar study design, given the effort and investment any population-based study entails.

First, there can be selection of more controls per case, which can improve the statistical power to estimate the association. This is one of the advantages of a population-based study which this study could also have taken advantage of. Second, it is vital to realize that Toxocara canis serology itself has a sensitivity of 78% and a specificity of 92% by enzyme-linked immunosorbent assay. The cross-reactions with other nematode infections (e.g., Ascaris lumbricoides, Stronglyloides) reduces its specificity further, particularly in tropical areas.[3] The association or the lack of it, does not really take us further, into Toxocara species and the occurrence of epilepsy. The sublime evidence still remains the lesion on imaging, which is putatively one of the parasites causing focal epilepsy. Studies looking at other parasites serology[456] are also fraught with the same limitation. The authors have indeed mentioned this as one of the limitations of their study. Third, the presence of asymptomatic calcified lesions in community dwellers in endemic areas and its association with parasitic serological studies will provide further insight into the etiopathogenesis of epilepsy. The community-based studies provide a high prevalence of asymptomatic calcified lesions (15.1%).[7] Thus, this study also provided an opportunity to image the cases and control population, to detect asymptomatic people (with positive or negative serology). This would have of course, entailed additional resources and budget, which becomes the challenge in conducting such studies. Last, and most importantly, the application of serology into clinical practice does not presently look tenable in patients with epilepsy, given that imaging provides better information and does not change management.

Nevertheless, conduct of such studies is vital for generating evidence regarding prevalence of infection as a preventable cause of epilepsy. This would drive the authorities for establishing prevention programs at population level. The authors need to be congratulated to have put efforts to provide this information.

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Conflicts of interest

There are no conflicts of interest.