THE PLANTAR REFLEX
Test: This is also known as the Babinski reflex. It is best evoked by a specific stimulation of the soles of the feet with a sharp object (like the end of a reflex hammer or a fingernail). In the video, you can see the examiner place a finger on the baby's heel and then run it along the lateral border of the sole. This motion can also be continued with the finger running underneath the toes toward the medial side of the foot (not shown in the video).
Normal response: A positive Babinski sign is observed- the big toe dorsiflexes and the other toes separate, or fan outwards. One must watch out for voluntary withdraw, which does not indicate a positive response - this is a response that can occur but is more delayed than the plantar reflex. A negative Babinski sign occurs when the toes flex downward - this occurs later in life in a normal infant and adult.
Neural circuit: Corticospinal tract Appears: birth
Disappears: <2 years
Abnormal persistence: >2 years
Abnormailities:
There are many causes of an positive Babinski sign, and thus its abnormality does not lead to a diagnosis. These include:
- Brain tumor of corticospinal tract or cerebellum
- Friedreich ataxia - an autosomal recessive neurologic disease that usually presents in adolescence. Some of the many symptoms include dysarthria, imbalance, and propioceptive sensory loss.
- Meningitis - inflammation of the membranes of the brain or spinal cord
- Hepatic encephalopathy - cirrhosis of the liver results in toxic substances into the sysmtic circulation, resulting in neurologic abnormalities
- Rabies - caused by a lyssavirus. Progressive neurologic disease that results in madness, aggressiveness, paralysis, and death.
- Syringomyelia - cavities of the spinal cord lined by gliogenous tissue that cause pain and parethesia in a cape like distribution.
