One of the important neuralgias is trigeminal neuralgia which is characterized by affecting predominantly the second [V2] and third [V3] distribution of the trigeminal nerve. It is most common in middle-aged women. Frequently there is an associated trigger point: touching specific parts of the face, chewing [or] a light breeze touching the face can result in pain characterized by a lancinating shooting, electric-like sensation that can last anywhere from a few seconds to a couple of minutes and recur multiple times daily. There is a strong association [between trigeminal neuralgia and] multiple sclerosis and, in order to make that diagnosis, the neurologic examination including a detailed examination of the trigeminal nerve [should be normal].

The next neuropathy that has been extensively evaluated in clinical trials is diabetic neuropathy. It is estimated that 10% of patients already have a neuropathy at the time the diagnosis of diabetes is made. Fifty percent will go on to develop a neuropathy during their lifetime. Not all neuropathies are painful, but about a third of them are associated with pain. The pain is commonly described as being superficial, predominantly burning, affecting the feet and hand, [and is] associated with allodynia, the perception of pain following an innocuous stimulus. But you can also have a shooting electric-like component of pain as well [as] a musculoskeletal cramping and aching component.

The [third] condition that was evaluated in clinical trials is post-herpetic neuralgia. This condition is defined as pain lasting for a month or more following crusting or healing of the characteristic zoster rash. It occurs in 9 to 14% of patients following a bout of acute zoster. This condition is very much age-dependent. As you can see, 50% of patients age 60 years of age or more go on to develop post-herpetic neuralgia as well as 75% of those 70 years of age or older.

It is slightly more common in women, probably a reflection of the fact that women tend to outlive us. And it has a predilection for the thoracic dermatomes as well as the ophthalmic division, the V1 distribution, of the trigeminal nerve. Whereas trigeminal neuralgia affects V2 and V3, post-herpetic neuralgia predominantly affects V1. The pain can be excruciating, characterized by steady burning, aching pain, as well as a paroxysmal lancinating, electric-like component.

This reviews the various classes of drugs that have been reported to have efficacy in the treatment of neuropathic pain. We typically tend to use antidepressants, anticonvulsants and antiarrhythmics, drugs such as mexiletine, topical formulations - capsaicin [and] lidocaine cream - and finally the opioids.

It's important at the onset to mention that there are a number of clinical features associated with painful neuropathies that need to be treated independently from the pain per se. Many patients with painful neuropathy tend to have insomnia because the pain is more severe at night and interferes with their ability to go to sleep. You can also have reactive anxiety and depression. And depression is extremely important because, if the patient is depressed, you can pretty much try every combination of drugs known in the books and it's unlikely that the patient will respond unless and until the depression is treated.

And obviously patients with chronic neuropathic pain have an overall decrease in their quality of life.