Babinski Sign

In 1896, Joseph François Félix Babinski (1857-1932) reported the clinical sign that now bears his name. Babinski noted that stimulation of the soles of the feet of some patients with unilateral paralysis induced, not the expected flexion, but rather the extension of the great toe on the paralyzed side (Babinski, 1896). Others had seen this reflex response, but Babinski was the first to recognize and call attention to its diagnostic importance, for example, in differentiating structural from hysterical paralysis (Babinski, 1898). He later pointed out that fanning of the lateral toes may accompany extension of the great toe (Babinski, 1903).

The sign is best elicited by having the patient lie supine with the leg uncovered and supported by the examiner. After informing the patient about what is to happen, a stimulus (ranging from light touch to moderately firm and slightly noxious pressure from a blunt object like a wooden applicator stick or key) is applied to the lateral plantar surface of the foot in a gentle, sweeping motion from heel to ball (van Gijn, 1995). The hallmark positive (extensor) response is mediated by contraction of the long extensor of the great toe (extensor hallucis longus). Careful observation for tightening of the extensor hallucis longus tendon may resolve doubts about whether the sign is present. Extensor responses can be evoked by stimuli applied to a number of other loci on the foot or leg, but the interpretation of the response is the same. Extension of the toe (away from the noxious stimulus on the sole) is part of a generalized flexion response of the stimulated limb, so visible flexion of thigh on hip, leg on knee, and foot on ankle may occur, brought about by contraction of the tibialis anterior, hamstrings, tensor fasciae latae, and iliopsoas muscles, respectively (Bassetti, 1995).

The clinical significance of the Babinski sign is found by reviewing its developmental course. Apositive response has been reported in 10-90% of normal newborns (Hogan & Milligan, 1971; Jaynes, Gingold, Hupp, Mullett, & Bodensteiner, 1997). The pyramidal tracts of the central nervous system, carrying neurons from the motor cortex into the spinal cord, subserve voluntary muscle function throughout the body. As these tracts mature during the first 6 months of life, the toe response changes from extensor to flexor by the age of 9-12 months (Katiyar, Sen, & Agarwal, 1976); the entire flexion response of the lower extremity is extinguished along with the Babinski response (van Gijn, 1995).

Since maturation of the pyramidal tracts underlies the developmental disappearance of the Babinski response, it is not surprising that persistence of the response after the first year of life—or its later reappearance, especially if laterally asymmetrical—indicates disease affecting the pyramidal tract. As Babinski knew, the sign often accompanies destructive lesions of the motor fibers innervating the foot; in these patients careful testing may reveal weakness of the affected limb or at least disturbances of fine motor function (Bassetti, 1995).

Now, more than 100 years after its initial description, the extensor response of the great toe remains one of the best known and clinically useful of the eponymic signs in clinical medicine. Its unilateral presence almost always indicates serious structural abnormalities of the upper motor neurons serving the affected limb. The finding of a positive Babinski response after the first year of life should be considered abnormal and appropriate neurological investigation should be undertaken to identify the nature and location of the abnormal process.

REFERENCES

Babinski, J. (1896). Sur le réflexe cutané plantaire dans certains affections organiques du système nerveux central. Comptes Rendus de la Société de Biologie, 48, 207-208. Babinski, J. (1898). Du phénomène des orteils et de sa valeur sémi-

ologique. Semaine Médicale, 18, 321-322. Babinski, J. (1903). De l'abduction des ortreils. Revue Neurologique

(Paris), 11, 728-729. Bassetti, C. (1995). Babinski and Babinski's sign. SPINE, 20, 2591-2594.

Hogan, G. R., & Milligan, J. E. (1971). The plantar reflex of the newborn. New England Journal of Medicine, 285, 502-593. Jaynes, M. E., Gingold, M. K., Hupp, A., Mullett, M. D., & Bodensteiner, J. B. (1997). The plantar response in normal newborn infants. Clinical Pediatrics, 36, 649-651. Katiyar, G. P., Sen, S., & Agarwal, K. N. (1976). Plantar response during infancy. Acta Neurologica Scandinavica, 53, 390-394. van Gijn, J. (1995). The Babinski reflex. Postgraduate Medical Journal, 71, 645-648.

Francis A. Neelon

Duke University Medical Center

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