Plantar reflex

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In medicine (neurology), the Babinski reflex or Babinski sign is a reflex that can identify disease of the spinal cord and brain. It is more properly called the plantar reflex, as Babinski's sign in reality only refers to the pathological form.

1 Methods
2 Interpretation
3 Relationship to Hoffmann sign
4 Eponym
5 See also
6 External links

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Methods

Image:Babinski's sign01.jpg The lateral side of the sole of the foot is rubbed with a sharp or hard implement (usually a series of pinpricks or the tip of a tendon hammer), running from the heel along a curve to the metatarsal pads. It is an unpleasant sensation for most. There are roughly three responses possible:

Flexor: the toes curve inwards and the foot pronates; this is the response seen in healthy adults. This is not a reflex; it is under voluntary control.
Indifferent: there is no response (sometimes a feature of peripheral neuropathy).
Extensor: the hallux (large toe) extends upwards, and the other toes to a lesser extent; this response is Babinski's sign.

In decerebrate patients, a more complex reflex is observed, which includes the lifting of the whole leg. This is a primitive reflex, indicating that the brain has been damaged severely.

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Interpretation

The extensor response can indicate damage of the spinal cord in the thoracal or lumbar region, or brain disease. Occasionally, a pathological plantar reflex is the first (and only) indication of a serious disease process, and a clearly abnormal plantar reflex often prompts detailed neurological investigations, including CT scanning of the brain or MRI of the spine, as well as lumbar puncture for the study of cerebrospinal fluid.

Young babies (less than a few months of age) will also show an extensor response. A baby's smaller toes will fan out, and their big toe will dorsiflex slowly. This happens because the corticospinal pathways (that run from the brain down the spinal cord) are not fully myelinated at this age, so the reflex is not inhibited by the cerebral cortex.

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Relationship to Hoffmann sign

The Hoffmann sign, also known as the finger flexor reflex, is occasionally said to be the upper limb equivalent of the Babinski's sign because both indicate upper motor neuron dysfunction. Mechanistically, they differ significantly; the finger flexor reflex is a simple monosynaptic spinal reflex involving the flexor digitorum profundus that is normally fully inhibited by upper motor neurons. The pathway producing the plantar response is more complicated, and is certainly not monosynaptic. This difference has led some neurologists to reject strongly any analogies between the finger flexor reflex and the plantar response.

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