Babinski’s Sign (1)
Babinski’s sign is a polysynaptic cutaneous reflex consisting of an extensor movement (dorsiflexion) of the big toe on eliciting the plantar response, due to contraction of extensor hallucis longus. There may be in addition fanning (abduction) of the other toes (fan sign; signe de l’éventail) but this is neither necessary nor sufficient for Babinski’s sign to be present. There may be simultaneous contraction of other limb flexor muscles, consistent with the notion that Babinski’s sign forms part of a flexion synergy (withdrawal) of the leg. The use of the term "negative Babinski sign" to indicate the normal finding of a downgoing (flexor; plantar flexion) big toe is incorrect, "flexor plantar response" being the appropriate description.
The plantar response is most commonly performed by stroking the sole of the foot, although many other variants are described (e.g., Chaddock’s sign, Gordon’s sign, Oppenheim’s sign, q.v.).
Babinski’s sign is normal in infants with immature (unmyelinated) corticospinal tracts; persistence beyond three years of age, or reemergence in adult life, is pathological. In this context, Babinski’s sign is considered a reliable ("hard") sign of corticospinal (pyramidal) tract dysfunction (upper motor neurone pathology), and may coexist with other signs of upper motor neurone dysfunction (e.g., weakness in a so-called pyramidal distribution, spasticity, hyperreflexia). However, if weakness of extensor hallucis longus is one of the features of upper motor neurone dysfunction, or from any other cause, Babinski’s sign may be unexpectedly absent although anticipated on clinical grounds. In the presence of extrapyramidal signs, it is important to distinguish Babinski’s sign, a "pyramidal sign", from a striatal toe (spontaneous upgoing plantar).
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Van Gijn J. The Babinski sign: a centenary. Utrecht: Universiteit Utrecht, 1996