Epidemiology of Symptomatic Chiari Malformation in Tatarstan: Regional and Ethnic Differences in Prevalence

Epidemiology can assess the effect of Chiari I malformation (CM1) on the neurological health of a population and evaluate factors influencing CM1 development.

To analyze the regional and ethnic differences in the prevalence of CM1.

The population of the Republic of Tatarstan (RT) in the Russian Federation was evaluated for patients with CM1 symptoms over an 11-yr period. Typical symptoms of CM1 were found in 868 patients. Data from neurological examination and magnetic resonance imaging (MRI) measurement of posterior cranial fossa structures were analyzed.

MRI evidence of CM1, defined as cerebellar tonsils lying at least 5 mm inferior to the foramen magnum, was found in 67% of symptomatic patients. Another 33% of symptomatic patients had 2 to 4 mm of tonsillar ectopia, which we defined as "borderline Chiari malformation type 1 (bCM1)." The period prevalence in the entire RT for symptomatic CM1 was 20:100 000; for bCM1 was 10:100 000; and for CM1 and bCM1 together was 30:100 000. Prevalence of patients with CM1 symptoms was greater in the northern than southern districts of Tatarstan, due to a high prevalence (413:100 000) of CM1 in the Baltasy region in one of the northern districts.

One-third of patients with typical symptoms of CM1 had less than 5 mm of tonsillar ectopia (bCM1). Assessments of the health impact of CM1-type symptoms on a patient population should include the bCM1 patient group. A regional disease cluster of patients with Chiari malformation was found in Baltasy district of RT and needs further study.