Neuropathic pain by definition is nerve injury pain. The most common presentation is diabetic peripheral and post herpetic neuralgia (Post-shingles pain). Neuropathic pain can occur with other conditions where there may or may not be a documented nerve injury. Failed back syndrome, which consists of continued back and leg pain usually following multiple surgical procedures, almost certainly has a neuropathic pain component. Anterior thigh pain without weakness may be a condition called meralgia paristetica. This is an injury to the lateral femoral cutanious nerve which runs medial to the “hip bone” as a result of a tight or heavy belt such as an electrician or a policeman wears. Often following an inguinal hernia repair, persistent pain may be from an injury to the ilioinguinal nerve. Some headaches can be a result of occipital neuralgia which is an injury to the nerve that goes to the back (occipital) area of the head. Finally, traumatic often to legs or arms can result in neuropathic pain.

What are the symptoms of neuropathic pain? Generally the pain is in the distribution of a nerve. It is distinctive in quality being sharp shooting like an electrical shock and/or burning. The pain is usually constant and never totally goes away. There may be numbness to touch in the area of the pain because the injured nerve is transmitting pain impulses to the brain in the place of normal sensory information (feeling) from the skin. There may be a hypersensitivity which is caused by changes at the spinal cord level due to bombardment of pain impulses from the injury. There may also be tissue changes in an extremity consisting of decreased temperature and swelling. This represents the involvement of the nerves that control dilation and constriction of blood vessels. This special condition was known as RSD (reflex sympathetic dystrophy) or causealgia. It is now called complex regional pain syndrome and will be discussed later.

In order to understand the treatment of neuropathic pain, I will briefly review the mechanism of pain transmission. Nerve injury can occur anywhere but usually happens to a peripheral nerve such as that of an extremity (arm or leg). Post herpetic neuralgia and failed back syndrome pain are injuries to nerve roots. Nerves of internal organs are most commonly injured by invasive cancers.

The pain impulses travel from the injured nerve to the spinal cord. This information can and often is modified at this level. The spinal cord is quite dynamic and actual changes take place as a result of the incoming information. These changes are called “wind-up” or central sensitization and results in an amplification of the pain impulses. The pain impulses then travel up to the brain where the severity of pain is determined. At this point in the discussion with my patients I assure them that this is normal physiology and does not mean the pain is “all in their head”.

In addition to the main pathway to the brain there are nerve tracts from the brain down to the spinal cord that can modify the transmission of pain impulses from the nerve injury to the brain. These descending modulating tracts (pathways) play an important role in the therapy for neuropathic pain.

Therapy can include both nerve blocks (injections) and medications. Doing an anesthetic nerve block to an injured nerve stops the pain impulses from getting to the spinal cord and on to the brain resulting in total pain relief. The anesthetic generally lasts five to eight hours; so how can long term pain relief result from these injections? Because the nerve blocks stop the constant flow of pain impulses to the spinal cord, the “wind-up” (central sensitization) can reverse itself resulting in decreased amplification of the signal to the brain and extended reduction of pain. Often it takes more than one nerve block to accomplish this; but if no pain relief results from the initial injection or if there is no progressive improvement with subsequent injections, they should be discontinued.

Nearly all forms of neuropathic pain require some medical management. A common error is to treat neuropathic pain with only pain medication (opiate or narcotic). This rarely works even at high doses. The use of the descending modulating pathways (nerve tracts from the brain to the spinal cord) is necessary to fully treat neuropathic pain. Stimulation of these pathways results in a reduction in the flow of pain impulses from the nerve injury to the brain at the level of the spinal cord.

There are two classes of medications used to stimulate this inhibitory pathway: anticonvulsants and antidepressants. Since each of these types of medications cause stimulation by different means, they are often used together for maximum effect.

The anticonvulsants commonly used are Tegretol, lamictal, gabapentin, lyrica, and others. Patients usually notice a “dulling” of the sharp shooting/electrical pain. These medications must be takenregularly as apposed to the pain medication which can be taken as needed. Abrupt discontinuation of these medications can result in a seizure in certain patients and should be avoided.

Antidepressants work two ways to treat neuropathic pain. First, they stimulate the inhibitory pathways. The common medications include the tricyclic antidepressants, amitriptyline and nortriptyline. They can be given at much lower doses then was previously used for the treatment of depression eliminating many of the side effects. The common side effect of sedation is beneficial for sleep with bedtime dosing. The newer antidepressants referred to as selective serotonin reuptake inhibitors (SSRIs) stimulate the decending inhibitory pathways but also treat depression and anxiety. Depression and anxiety are often associated with chronic pain and when uncontrolled can affect the perception of pain at the brain level. For example the anxiety created by a visit to the dentist can result in a higher level of pain. The second effect of antidepressants is with SSRIs which modulate the influx of pain impulses to the brain and also treat depression and anxiety.

Pain medication (opiate/narcotic) works mostly at the spinal cord level to reduce the transmission of pain impulses to the brain. Antiinflammatory medications (Ibuprofen, Aleve) may also work at the spinal cord level in a similar but minor way. Pain medication is commonly thought to be “the only thing that works” because of the immediate profound results. The benefits of the anticonvulsants and antidepressants are more subtle and many don’t realize the benefit until they are discontinued. I think that when the diagnosis of neuropathic pain is made the treatment should always include an anticonvulsant, an antidepressant, and a pain medication as needed.

RSD or causalgia occur when the nervous system (sympathetic) that controls the blood vessels is involved, with or without a documented nerve injury. The new medical term for this condition is complex regional pain syndrome (CRPS). This system has to be “reset” and since this system also carries pain impulses, treatment is imperative. The treatment involves a special type of nerve block (anesthetic injection) that causes dilation of all blood vessels of the arm or leg. After the block wears off in two to five hours, the system should return to normal where constriction occurs when it’s cold and dilation when it’s warm. It may take three to four injections with progressive improvement. It’s critical that this condition be treated in the first six months after onset because it becomes more resistant to therapy after that.

In summary if you have burning, sharp (electrical) pain with numbness or hypersensitivity most likely its neuropathic pain. Your primary care provider can refer you to a board certified pain specialist who can evaluate and treat neuropathies.