To elicit this sign, the examiner strikes the patient’s sole using a blunt orange stick, starting from the heel, along the lateral border of the sole then medially to the base of the first toe. As one can see from the two videos, the patient demonstrates dorsiflexion of the big toe when testing for the sign. In some patients, there may also be fanning of the toes which is not very obvious in these two cases. Sometimes, the sign can also be elicited by striking other areas of the lower limb, such as the tibia and the ankle. The patient in the first video had a severe right cortical infarct resulting in left-sided upper motor neuron signs, whilst the patient in the second video had a history of transverse myelitis due to neuromyelitis optica resulting in upper motor neuron signs of both lower limbs.
Discussion of the sign
Up-going plantar reflex, or a positive Babinski’s sign, is considered a ‘hard’ neurological sign, which are signs that are objective and difficult to mimic. It is an upper motor neuron sign and any lesion along the cortico-spinal tract from the motor cortex to the spinal cord may result in this phenomenon. It has been proposed that loss of upper motor neuron control to local spinal circuits reproduces this primitive plantar reflex. It may be physiological in children before 1 year of age, but is otherwise pathological in older individuals, where the normal plantar response is downgoing. Of note, is that the foot should be fixed when eliciting the sign to minimise a withdrawal response, and the first direction of toe movement should be noted.
Also, as eliciting the sign often causes discomfort to the patient, it is preferable to use the blunt end of an orange stick when examining for the sign. Use of sharp objects (e.g. keys, pens or the sharp end of a tendon hammer) is discouraged. It is also of courtesy to warn the patient, whenever possible, that there will be some discomfort whilst testing for the sign.