Accuracy of the Babinski sign in the identification of pyramidal tract dysfunction.

Overview

BACKGROUND: The extensor plantar response described by Joseph Babinski (1896) indicates pyramidal tract dysfunction (PTD) but has significant inter-observer variability and inconsistent accuracy. The goal of this study was to determine the accuracy of the Babinski sign in subjects with verified PTD. METHODS: We studied 107 adult hospitalized and outpatient subjects evaluated by neurology. The reference standard was the blinded and independent diagnosis of an expert neurologist based on anamnesis, physical examination, imaging and complementary tests. Two neurologists elicited the Babinski sign in each patient independently, blindly and in a standardized manner to measure inter-observer variability; each examination was filmed to quantify intra-observer variability. RESULTS: Compared with the reference standard, the Babinski sign had low sensitivity (50.8%, 95%CI 41.5-60.1) but high specificity (99%, 95%CI 97.7-100) in identifying PTD with a positive likelihood ratio of 51.8 (95%CI 16.6-161.2) and a calculated inter-observer variability of 0.73 (95%CI 0.598-0.858). The intraevaluator reliability was 0.571 (95%CI 0.270-0.873) and 0.467 (95%, CI 0.019-0.914) respectively, for each examiner. CONCLUSION: The presence of the Babinski sign obtained by a neurologist provides valid and reliable evidence of PTD; due to its low sensitivity, absence of the Babinski sign still requires additional patient evaluation if PTD is suspected.