CHRONIC PAIN GENERAL TREATMENT PRINCIPLES
Once pain has been present for a period of time, the dorsal horn of the spinal cord is thought to be altered, perhaps permanently. Wide dynamic range neurones in the deeper levels of the dorsal horn are "wound up" stimulating other nociceptor cells. This increases the receptive field which widens the area over which pain is felt. This explains the glove and stocking distribution of pain felt in some neuropathic pain syndromes, e.g., diabetic neuropathy, or sympathetically maintained pain. This "pain memory" is thought to explain why pain remains chronic.
Unfortunately there is no medication, as yet, to turn off this "wind-up" of the central nociceptors. Recent research has concentrated on NMDA (N methyl D aspartate) receptors on the WDR neurones. These are thought to be important for pain memory. New medications are in the development stage to antagonize these receptors and, hopefully, diminish the pain sensation.
PHARMACOLOGICAL
Analgesics: Simple analgesics such as tramadol, maximum dose 100 mg q.i.d.,
acetaminophen-opioid combinations up to a maximum of 4 grams of acetaminophen a day, are all useful and can be trialed in patients with chronic pain. Any improvement of reported pain should be accompanied by an improvement in function. In chronic pain, unlike malignant pain, the analgesic requirements should remain fairly constant with time. A rapid escalation in pain requirements usually means either progression of the disease, or an environmental stressor has worsened the pain perception.
Antiarrhythmics: Certain antiarrhythmics, such as the sodium channel blocker mexilitine, which is converted to a lidocaine-like substance in the liver, calcium channel blockers and beta blockers have been used for treatment of various pain disorders. Mexilitine has been used for centralized neuropathic pain and is often effective in treatment of diabetic neuropathic pain. Calcium channel blockers and beta blockers have been used in prophylaxis against migraines.
Anticonvulsants: Chronic pain, especially that associated with shooting, "lancinating" pains, has been likened to the epilepsy of the spinal cord. Thus, drugs such as carbamazepine, phenytoin, valproic acid or lamotrigine can be trialed. Whereas most of the anticonvulsants are sodium channel blockers, gabapentin works on an entirely different pathway possibly via the inhibitory GABA system.
Opioids: Opioids can be extremely effective in the management of chronic pain. The risk of addiction is low and toxicity is minimal. The side effect of constipation is, however, unavoidable in most patients and, when giving opioids, a second prescription should routinely be given for laxatives. It is also worthwhile to have an "opioid agreement" with the patient. This stipulates that the patient will only get opioids from one physician, will ask permission prior to increasing the dose and will take care not to lose the prescription. The patient also consents to random drug testing should this be considered necessary. If one type of opioid is unsuccessful a second class of opioid can be tried. Thus, if morphine is not successful methadone, a fentanyl patch or hydromorphone (dilaudid) could be trialed. If aberrant behavior or prescription loss occurs, the physician retains the right to wean the patient and discharge him or her from his care. To wean a patient without withdrawal symptoms means withdrawing the medication at a rate between 20-50% per day. After one week, most patients can be taken off even large doses of opioids successfully.
NONPHARMACOLOGICAL
Coping skills and relaxation: By releasing various neuropeptides, relaxation and improving coping skills can dampen the pain response. They allow the patient to have a quality of life despite pain.
TENS: This should be trialed on an organized basis for one week. If pain relief
does not occur after this time, TENS will probably be ineffective.
Acupuncture: If acupuncture is going to be successful, 50% of patients respond
within three treatments and probably 90% within six treatments. If no improvement occurs after six treatments, given initially bi-weekly and then weekly, therapy should be discontinued. Acupuncture may be with needles only, or with needles and electrical stimulation. If the patient responds well to acupuncture, the duration of pain relief varies. Periodic booster treatments are usually required.
Physical therapy: Specific stretching and mobility exercises, as well as an aerobic exercise program should be given.
Others: There are many other treatments for pain. For example, there is some evidence that magnets placed over trigger point areas, or over the nerve serving the area, may decrease pain. This is probably by central neuromodulation.
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