The Different Types of Nerve Damage

The term ‘nerve damage’ gets thrown around a lot and can sound scary. However, there are different types of nerve damage which greatly influence the prognosis, as you’ll see. One of the most useful ways to understand nerve injuries comes from a classification developed by neurologist Herbert Seddon in the 1940s. He divided peripheral nerve injuries into three major categories: neurapraxia, axonotmesis, and neurotmesis.

Neurapraxia: The Nerve Is Temporarily Blocked

Neurapraxia is the mildest form of peripheral nerve injury. In this situation, the nerve itself has not been completely disrupted. Instead, its ability to transmit an electrical signal becomes temporarily impaired, often because of compression, stretch, or irritation.

Think of it almost like a kink in a garden hose. The hose is still intact, but flow through it has been interrupted. This can happen after sleeping in an awkward position, prolonged compression of a nerve such as sitting on a hard surface for a long time, or relatively mild trauma.

Typical symptoms include numbness, tingling, burning, weakness, or temporary loss of muscle function in the area supplied by that nerve. The important distinction is that the axon, the long portion of the nerve responsible for carrying the signal, remains structurally intact.

Neurapraxic injuries generally have the best prognosis. Once the underlying irritation or compression resolves and the nerve restores normal conduction, function can return without the nerve having to regrow all the way to its target. Recovery may occur over days to weeks, although some injuries can take longer depending on their severity.

Axonotmesis: The Nerve Fiber Has Been Damaged

Axonotmesis is a more significant injury. Here, the axon itself has been disrupted, even though some of the connective tissue structures surrounding the nerve may remain intact.

This distinction matters because the portion of the axon downstream from the injury can no longer survive normally. It undergoes a process called Wallerian degeneration, where the damaged distal portion of the nerve breaks down and is cleared away.

The nerve then has to regenerate. Fortunately, peripheral nerves have some ability to do this. If the structures surrounding the nerve remain sufficiently intact, they can essentially provide a pathway that helps guide the regenerating axon back toward its original destination.

This is a much slower process than recovery from neurapraxia. Regenerating peripheral axons may progress at roughly 1 millimeter per day, although actual recovery varies depending on the nerve, location and severity, age, health of the individual, and distance between the injury and the muscle or sensory tissue it needs to reach. This is why an injury close to the hand or foot may recover differently from an injury occurring much higher up the arm or leg.

Neurotmesis: The Nerve Has Been Severely Disrupted

Neurotmesis is the most severe category in Seddon's classification. The nerve and its supporting structures have been significantly disrupted or completely divided. Now the regenerating axons no longer have an intact pathway leading them back to their original destination.

Imagine cutting through an electrical cable rather than simply pinching it. Even if the individual wires attempt to reconnect, they may not know where they are supposed to go. That is why recovery is much less likely.

Some neurotmetic injuries require surgical evaluation and potentially nerve repair, grafting, or other procedures to restore continuity and give regenerating nerve fibers a pathway toward their target. The earlier a significant nerve injury is properly identified, the better clinicians can determine whether rehabilitation is appropriate or whether surgical consultation is necessary.

How Do We Determine What Type of Nerve Injury Has Occurred?

In physical therapy, we have ways to tell what nerve is affected. There are myotomes and dermatomes. These are images that you can google. For example, L3 refers to the knee (that’s how we remember it, ‘L3 to the knee’). Reflexes can help determine what nerve root is affected. Strength testing works in a similar way. 

If you see a neurologist, they will likely perform a nerve conduction studies and electromyography (EMG) which can provide additional information about how effectively nerves are conducting electrical signals and whether the muscles they supply show evidence of denervation or reinnervation.

Timing matters here as well. Some electrical changes associated with axonal injury take time to become detectable, which means an EMG performed very soon after an injury may provide different information than one performed several weeks later. Imaging such as ultrasound or MRI may also be useful in selected cases when clinicians need to evaluate the physical structure of the nerve or identify something compressing it.

Nerve Healing Is Not the Same as Muscle Healing

This is an important distinction. A strained muscle can often heal relatively quickly because the damaged tissue is local. An axonal nerve injury may be very different. If a nerve is injured near the shoulder but supplies muscles in the hand, regenerating nerve fibers may have a considerable distance to travel before they can reinnervate those muscles.

That means someone can be improving biologically even before they notice substantial improvements in strength. During that time, rehabilitation isn't simply about “strengthening the weak muscle.”

The bigger picture may include maintaining joint mobility, preserving the health of affected muscles, preventing compensatory movement patterns, maintaining function in unaffected tissues, addressing mechanical contributors to the nerve injury, and gradually retraining movement as nerve function returns.

The phrase “nerve damage” is not a prognosis. A temporarily compressed nerve, an injured axon with an intact pathway, and a completely disrupted nerve are fundamentally different problems. That is why understanding where the nerve is injured, how severely it is injured, and which structures remain intact is so important.

The goal is not simply to identify that a nerve is involved. It is to understand what happened to the nerve and what environment we can create to give it the best opportunity to recover. We also want to figure out what mechanical stressors or movements are causing it, and temporarily avoid that activity.