The "toe phenomenon", or extensor toe sign, is characterized by the extension (dorsiflexion) of the great toe elicited by plantar stimulation, and indicates pyramidal tract dysfunction. This phenomenon was first extensively described and studied by Joseph Jules François Félix Babiński (1857-1932), who introduced it in clinical practice. In 1912, the famous Italian neurologist Camillo Negro (1861-1927) proposed a new method of eliciting the extensor toe sign by inviting the patient, lying in bed in dorsal decubitus position, to raise the paretic limb with the leg extended on the thigh. This sign appeared during voluntary effort and could not be elicited by raising the unaffected lower limb. Negro was also the first to investigate the influence of cold upon the appearance of the "toe phenomenon" and to propose the use of (faradic) electrical stimulation to evoke it.
Keywords: Babiński sign; Camillo Negro; Clinical semiology; History of neurology; Joseph François Félix Babiński.
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