Posted on 14 Oct 2012 03:39
The Babinski reflex or Babinski sign is pathalogical (altered or abnormal) reflex of the lower limb which indicates damage to the corticospinal tracts of the spinal cord. These pathways are also called the pyramidal tracts after the pyramid-shaped parts of the medulla oblongata through which they pass. To elicit the Babinski reflex, an examiner forcefully strokes the edge of the bottom of a patient's foot (lateral plantar surface or sole) with a moderately sharp object from the heel to the toes. The Babinski reflex is named after its discoverer, Joseph Babinski, who described it in 1896.
The normal response to this stimulus is plantar flexion of the foot and toes, called the plantar reflex. This means that the foot and toes will flex or 'curl' away from the leg. In the Babinski reflex, much the opposite happens and the big toe extends upwards toward the leg, called dorsiflexion, while the other toes fan out. This response, it should be noted, is normal in infants up to 12 months of age and this is simply thought to show the immaturity of their corticospinal pathway. It should start to wane between 6 to 8 months of age and disappear after one year. In infants, the Babinski reflex is usually classified in a group of reflexes called primitive or infantile reflexes, which are present at birth and later disappear; or change in the case of the Babinski reflex.
When a positive Babinski reflex is found in adults, it is considered a clinically positive sign of corticospinal damage. It is possible for this response to be triggered in some patients by other noxious stimuli such as loud noise, pain, or just a bump on the bed. Sometimes, as well, it can be elicited by stroking other parts of the foot. The sign may be only on one side or on both, may start out unilateral and progress to bilateral, and it may be temporary or permanent. A temporary Babinski reflex tends to occur during the postical, or third, phase of a seizure. With corticospinal damage, the sign is more likely to be permanent.
Positive Babinski Sign
Sometimes, despite other evidence of corticospinal tract damage, an equivocal (unclear and hard to interpret) Babinski is found. When this happens other signs are sought such as the following:
- Chaddock reflex: Babinski reflex caused by stimuation of the skin over the lateral malleolus, the bony prominence of the side of the ankle.
- Oppenheim sign: the Babinski reflex caused by a very instense stroke along the edge of the tibia from the knee downward
- Gordon sign: Babinski sign evoked by pressing or firmly squeezing the calf muscles.
- Rossolimo sign: Flexion of the second through fifth toes (toe flexor reflex) caused by a tap on the bottom of the distal phalanges (the ends of the toes). This is not a perfectly reliable indication of a corticospinal tract lesion.
These additional tests are not needed if the classic Babinski reflex is present and unequivocal, and there is other evidence of pyramidal tract damage. The lack of any toe movement at all, called Mute soles, in response to the Babinski test can be a beginning stage of the Babinski reflex in some patients. But in other patients it can be clinically meaningless. A "negative Babinski reflex" is a confusing term because of the word negative, but it would actually mean that the response, plantar flexion, was normal. A positive Babinski sign is actually the sign of damage.
Babinski Sign in a Normal Infant
The normal reflex to this kind of stimulus to the bottom of the foot is known as the plantar reflex. There are several other important lower limb reflexes which examiners use in neurological testing such as the knee-jerk reflex (patellar tendon reflex or quadriceps femoris reflex), the tibialis posterior reflex, foot extensor reflex (peroneus muscle reflex), ankle-jerk reflex (achilles reflex, triceps surae reflex), and biceps femoris reflex.
The corticospinal pathway (lateral and anterior "tracts") is one of the ascending tracts of the spinal cord. These tracts are responsible for conducting impulses from body parts and carrying sensory information to the brain (the descending tracts carry motor impulses from the brain to the muscles an glands). The corticospinal tracts carry motor impulses to the spinal nerves and to various skeletal muscles and so are involved in voluntary movement.
Hoffman's sign is the upper limb equivalent of Babinski's reflex. Here, the examiner holds the patient's middle finger and gives the middle phalanx of the finger a strong flick. If the thumb of the same hand spontaneously flexes in response, this is a positive sign and it raises suspicion of an upper neuron lesion. Both the upper and lower limbs would be affected, so the Babinski test is usually performed.
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