Overview of the Peripheral Nervous System
The peripheral nervous system consists of many different parts. The sensory neurons have various end organs that send a message for touch, heat, position, vibration, and pain to the spinal cord when activated. The motor neurons connect the spinal cord to the muscle to control movement. The autonomic neurons send messages to various organs to help control certain regulatory functions (such as temperature control and blood pressure control). The peripheral nerves consist of the axons of the various neurons (motor, sensory, and autonomic), as well as the insulating blankets (myelin).
Treatment of Painful Diabetic Polyneuropathy
The number one cause of damage to the peripheral nerves in the United States is Diabetes. The most common type is referred to as a polyneuropathy. In a diabetic polyneuropathy (sometimes referred to as painful diabetic neuropathy), the patient will typically present with burning or stinging feet, usually worse at night. The nerves to the feet are affected first because the damage is occurring along the entire length of the axons and the axons to the feet are the longest in the body. As the polyneuropathy progresses, the patient is commonly left with numbness and eventually weakness. As the neurons die, the pain typically moves up the legs.
About the time the first symptoms begin to appear around the knees, the symptoms begin in the hands. Fortunately, we have many good treatments for this type of neuropathic pain. Until 2004, no drug was FDA approved for the treatment of painful diabetic polyneuropathy. The first drug to gain FDA approval for this indication was Cymbalta® or duloxetine. Within a matter of months, Lyrica® or pregabalin was also approved for painful diabetic polyneuropathy. Neurontin® is also a commonly used medication.
Historically, diabetic neuropathic pain was treated with some of the older tricyclic antidepressants (amitriptyline or Elavil, nortriptyline or Pamelor). These medications, however, sometimes cause too many side effects including weight gain, constipation, and sleepiness. Usually these symptoms are now treated with anticonvulsants including Neurontin® or Lyrica® or the newer antidepressant Cymbalta®. These medications usually allow good control of the pain without side effects in many patients. Other medications less commonly used include clonazepam (Klonopin), tramadol (Ultram), and capsaicin cream (multiple trade names). For most patients, meaningful pain relief can be obtained. Unfortunately, the underlying nerve damage cannot be directly attacked with medication at this time.
The most important long-term treatment of the diabetic polyneuropathy is to achieve excellent diabetic control (Glycosylated Hemoglobin < 7%).
Diabetic Amyotrophy refers to another type of nerve damage. In this situation, there is usually a period of upper leg and back pain followed by weakness of the muscles of the upper leg. This typically occurs in patients who have had their diabetes poorly controlled. Once the weakness begins, usually the pain subsides. Recovery is spontaneous although in severe cases some physicians would treat with IVIG. Generally this treatment is used to speed up recovery in disabled patients. Again, excellent diabetic control is needed to help prevent future occurrences.Diabetic thoracic neuralgia refers to a form of chest pain or abdominal pain that occurs in diabetics. It is caused by injury to one of the peripheral nerves that comes out of the thoracic area of the spine and wraps around the side to the front of the patient. Typically the pain is described as sharp, shooting, or burning pain around from the back to the front. It is important to rule out other causes of the pain but many patients I have seen have had numerous testing because their physician did not recognize the cause of their pain. The treatment is similar to that of diabetic polyneuropathy.