Neuropathic Pain

Neuropathic pain is a complex, chronic pain state.  It can be associated with damaged tissue, including damage to the nerve fibres themselves. Because of this damage, the nerves can misfire, making the pain seem severe, or as if it is coming from other sites in the body. There may also be changes in the way the spinal cord and brain process pain, causing a condition known as ‘central sensitisation’. Over time, this leads to an increase in pain due to a ‘wind-up’ of the nervous system which remains in a state of increased sensitivity.

There is strong evidence that some anticonvulsant and antidepressant medications can be effective in treating certain neuropathic (nerve) pain conditions including postherpetic neuralgia (pain after shingles), painful diabetic neuropathy and trigeminal neuralgia.

It is difficult to apply this evidence to the use of these medications for osteoarthritis pain as it is not considered to be a neuropathic pain condition. However, it is now thought there may be some neuropathic pain present in some patients with OA.

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Medications used for neuropathic pain include anticonvulsants (medications for epilepsy) and antidepressants (medications used for depression).

The mechanism by which these medications work means they may also provide relief of pain due to nerve damage or dysfunction. The two most commonly used anticonvulsants are gabapentin (Neurontin) and pregabalin (Lyrica). Antidepressants commonly used for neuropathic pain include amitriptylline (Endep), nortriptylline (Allegron) and duloxetine (Cymbalta).

Be Aware

If there is some neuropathic pain present, it may be helped by these medications. It is very difficult to predict whether these medications will be effective for any particular patient. Even in known neuropathic pain conditions such as post herpetic neuralgia, painful diabetic neuropathy and trigeminal neuralgia these medications are only effective in about one-third of cases.

Side effects from these medications are common and include dizziness, sedation, dry mouth, weight gain, loss of concentration, nausea and constipation.

Any use of these medications for osteoarthritis pain must be considered a trial. The medication should be started at a low dose and gradually increased to assess its effectiveness. If side effects develop, the medication may need to be stopped. If the maximum dose is reached with no improvement in pain after a suitable trial period, the medication should be gradually reduced and stopped. It may take up to two months to fully assess whether these medications are helping.