What Is Paralysis?

Occurs when there is damage to a peripheral nerve in the arm or leg.

When a peripheral nerve in the arm or leg is injured, that is an injury to the axon of the lower motor neuron. The axon that is cut, which was formerly connected to the muscle, degenerates. The muscle fibers therefore lose their axon connection and can no longer receive a signal to contract. That muscle will become flaccid and cannot move. Over time the muscle will atrophy and lose its potential for recovery. After a year or two it is irretrievably lost.

Lower motor neuron injuries must be addressed within months after they occur. That is because of the degeneration of the muscles. Once those muscles are lost, they cannot be recovered. Research is ongoing to lengthen this window and to find out if there are ways to recover muscles late after the injury, but this is not yet available. Today, nerve grafting and nerve transfers are the primary treatment if we have the opportunity to treat these within the allotted time window. When this time window expires, we can still consider tendon transfers and, in some cases, muscle transplants as an option in many cases.

Occurs when there is injury or damage of the brain or spinal cord.

When the central nervous system is injured, we primarily think about an upper motor neuron injury as the reason for paralysis. For example, a stroke will destroy the cell bodies in the brain and they can no longer connect with the lower motor neuron in the spinal cord. Similarly, a spinal cord injury will interrupt the axon traveling from the brain which causes it to lose its connection with the upper motor neuron. In these cases, the muscle connected to the spinal cord can contract, but the brain no longer has normal control. Reflexes remain present, muscles are often tight, and spasms are common. This is because the lower motor neuron continues to function but does not receive proper control from the brain.

In an upper motor neuron injury, there is no urgency to undergo surgery. The lower motor neuron is alive and well and maintains that muscle so that if it ever receives communication again from above, it can once again function. Because of this, we prefer to wait before undertaking surgery. Therapy should be pursued aggressively. Plasticity can result in quite a bit of recovery. Plasticity refers to the ability of the central nervous system to rewire itself so as to better communicate with the lower motor neurons in a useful way. Plasticity is driven by demand – that is, if you are not actively trying to perform better, then plasticity is probably not being effectively promoted. Practice, practice, practice – that leads to more plasticity and better recovery. That being said, many patients stop improving before they reach adequate function. Therefore, after a year or two of hard work, you may find that you simply are not making more gains. This is when it is time to consider treatment. This may begin with Botox injections to temporarily reduce spasticity. Some people will make a lot of progress with this, others will require surgery. These patients should consider selective peripheral neurotomies. This is a procedure where the nerves are trimmed to eliminate the problematic spasticity but in a way that is very specific and maintains the function of the muscle.

Some patients with upper motor neuron injuries can recover useful function by means of a nerve transfer or tendon transfer. We have had success with these even 15 years after a spinal cord injury.

Results from a trauma that affects the descending axons of the upper motor neuron and the cell bodies of the lower motor neuron.

In injuries to the spinal cord, both the descending axons of the upper motor neuron and the cell bodies of the lower motor neuron are affected by the same trauma.

These two different types of injuries need to be managed according to their injury type. Refer to the upper and lower motor neuron sections above for more details on possible treatment options.

Lower motor neuron injuries should be treated early (before six months) for the best results. These include nerve injuries, brachial plexus injuries, and some spinal cord injuries. In fact, patients with spinal cord injury typically have a portion of their paralysis that is a result of a lower motor neuron injury and thus should be evaluated early.