Nerve damage. Not a pleasant thing to think about but important to discuss. I saw a patient several years ago with a foot drop from a herniated disc in his lumbar spine. The muscle that moved his ankle had complete atrophy.
As it turns out he had significant nerve damage. Despite a microdiscectomy, which helped his leg pain, his muscle atrophy never recovered. What is nerve damage and what are different types you should know? Here are 5 key points to understand about nerve anatomy and damage.
Nerve anatomy. A peripheral nerve refers to a nerve that leaves the spinal cord and exits down the extremities or trunk. A peripheral nerve has several layers. The outer layer is known as the epineurium. Inside the nerve are two further linings, the perineurium and theendoneurium. Individual nerve fibers run within the endoneurium and are known as axons.
Axon anatomy. Around an individual axon are cells that make myelin. Myelin is like the coating of a wire in your house. Myelin helps insulate and conduct electrical signals down the nerve to move the muscles in the arms and legs. The major peripheral nerve, such as thesciatic nerve, have a combination of sensory and motor fibers that are surrounded by myelin.
Nerve injury. There are three types of nerve injury to know with a peripheral nerve. These are neuropraxia, axonotmesis and neurotmesis. In a neuropraxia, there is a bruise to the nerve. This is the most common type of nerve injury I see in the office. A neuropraxia leads to injury to the myelin because of compression. This can lead to sensory and/or motor loss of function. An example would include compression from a herniated disc or from spinal stenosis. When the compression is removed, the nerve can recover over weeks to months. Axonotmesis is a more involved type of nerve injury where some of the individual axons die. The most severe form of nerve injury is when the nerve is actually cut in half. This is known as neurotmesis. Fortunately, I don’t see many cases of neurotmesis.
Nerve recovery. The key point with different types of nerve injury is to provide an optimal environment and time for the nerve to recover. For a neuropraxia, observation is typically the prescribed treatment. When I see patients in the office who have a foot drop from a herniated disc, I will recommend surgery if the foot drop does not improve. This is to remove pressure off the nerve to allow maximal recovery. If is important to emphasize the point that each nerve injury is different. Sometimes a herniated disc can cause so much damage that axonotmesis can be extreme. This is the case I described above. When I see atrophy in the muscle innervated by the nerve, that is a poor sign. It means that individual axons in the nerve have been lost.
Prompt diagnosis and treatment. When you notice in yourself or someone you know weakness or numbness that persists, get evaluated. If I am concerned regarding a diagnosis or if there is severe nerve damage, an EMG and nerve conduction test may be appropriate. This is to document what type and degree of nerve injury.
Often with nerve damage, there is a waiting game. An adult peripheral nerve has been estimated on average to regenerate approximately 1 mm per day. That’s watching the grass grow. If on average there is 1 mm per day regeneration, you can understand that many nerve injuries can take over a year to recover. If requires patience and aligning with a clinician you trust to walk you through the diagnosis and treatment for your individual condition. So that is a brief introduction to nerve damage and recovery.