CCSVI prevalence in study subjects on Doppler sonography.

Legend: CCSVI – chronic cerebrospinal venous insufficiency; VH - venous hemodynamic criteria. Subjects who fulfilled exactly one of the 4 VH criteria and were not assessed on one VH criterion were classified originally as CCSVI borderline [11]. In the present study, 21 (8.3%) fell into this category. These individuals were conservatively categorized as CCSVI negative in the statistical analyses, potentially biasing associations toward the null. CCSVI frequency differences between males and females were tested using the chi-square test.