Background: The Babinski sign is a well-known sign of upper motor neuron dysfunction that is widely considered an essential element of a complete neurologic examination. Little is known about reliability and validity of this sign. A less well-known sign of upper motor neuron dysfunction, decreased speed of foot tapping, also has not been carefully evaluated. Scientific evaluation of findings of the physical examination is crucial in directing busy clinicians.
Methods: Ten physicians (five neurologists and five non-specialists) examined each foot of 10 subjects, 8 of whom had known unilateral upper motor neuron weakness, 1 had bilateral leg weakness secondary to ALS, and 1 had no known neurologic deficits. Our main outcome measures were inter-rater reliability (kappa values) and accuracy (agreement with known upper motor neuron weakness).
Results: The reliability of the Babinski sign was fair (kappa 0.30) and was substantial for foot tapping (kappa 0.73). Agreement with known weakness was 56% for Babinski sign and 85% for foot tapping. Reliability and accuracy for both tests were similar for neurologists and non-specialists.
Conclusions: The interobserver reliability and validity of the Babinski sign for identifying upper motor neuron weakness are limited. Slowness of foot tapping may be a more useful sign.