What is Entrapment Neuropathy?
Entrapment neuropathy, also known as nerve compression syndrome or compression neuropathy, is a medical condition caused by direct pressure on a nerve. It is commonly known as a trapped nerve, though this may also refer to nerve root compression (by a herniated disc, for example).
Its symptoms typically include:
- Muscle weakness
The symptoms typically are present in just one particular part of the body, depending on which nerve is affected. Nerve conduction studies help to confirm the diagnosis. In some cases, surgery may help to relieve the pressure on the nerve but this does not always relieve all the symptoms. Nerve injury by a single instance of physical trauma is in one sense a compression neuropathy, but is not usually included under this heading.
What are the Causes?
A nerve may be compressed by prolonged or repeated external force through a number of actions, including:
- Sitting with one’s arm over the back of a chair (radial nerve)
- Frequently resting one’s elbows on a table (ulnar nerve)
- An ill-fitting cast or brace on the leg (peroneal nerve)
Part of the patient’s body can cause the compression, and the term entrapment neuropathy is used particularly in this situation. The offending structure may be a well-defined lesion such as a tumor (for example a lipoma, neurofibroma or metastasis), a ganglion cyst or a haematoma. Alternatively, there may be expansion of the tissues around a nerve in a space where there is little room for this to occur, as is often the case in carpal tunnel syndrome. This may be due to weight gain or peripheral oedema (especially in pregnancy), or to a specific condition such as acromegaly, hypothyroidism or scleroderma and psoriasis.
Some conditions cause nerves to be particularly susceptible to compression. These include diabetes, in which the blood supply to the nerves is already compromised, rendering the nerve more sensitive to minor degrees of compression. The genetic condition HNPP is a much rarer cause.
What are the Symptoms?
Typical symptoms include tingling, numbness, and/or a burning sensation in the area of the body affected by the corresponding nerve. These symptoms may occur directly following the injury, or may occur several hours or even days afterwards. It is important to note that pain is not a common symptom of nerve entrapment.
What are the Treatments?
Conservative measures should be tried first in most cases of entrapment neuropathy. Conservative management mainly consists of educating the patient to adopt avoidance behaviors. This seldom is practical in young, physically active patients, especially if symptoms are occupation-related. In cases of posterior interosseus nerve entrapment at the elbow caused by certain kinds of prosthetic devices (eg, Canadian crutches), redesigning or substituting the device may result in relief. Wrist splints for CTS are commonly prescribed but rarely provide long-term control.
Conditioning exercises and periodically injecting around the nerve with bupivacaine and dexamethasone may accord long-term relief.
Surgery is recommended for patients with symptoms refractory to non-operative measures and/or those with severe and long-standing symptoms or weakness.
The general principle of operative intervention is to decompress nerves in zones of compression. In some cases, surgical beds may be improved, or nerves can be transposed.