Practicing Pain Management: Finding Relief for Your Patients

Pain is a universally understood sign of disease and the most common symptom bringing people to seek medical attention. The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience" associated with actual or potential tissue damage. It is possible to describe different types of pain, and they tend to present differently. The history and physical examination help to identify these differences. Precise and systematic pain assessment is required to make the correct diagnosis and thus establish the most efficacious treatment plan for patients presenting with pain.

The somatosensory system (shown) is the part of the sensory system concerned with the conscious perception of touch, pressure, pain, temperature, position, movement, and vibration arising from the muscles, joints, skin, and fascia. It is a 3-neuron system that relays sensations detected in the periphery and conveys them via pathways through the spinal cord, brainstem, and thalamic relay nuclei to the sensory cortex in the parietal lobe. Impulses are carried from receptors via sensory afferents to the dorsal root ganglia, where the cell bodies of the first-order neurons are located. Their axons then travel through the spinal cord either in an ipsilateral or a contralateral fashion. Second-order neuron cell bodies are located in different anatomical areas depending on the sensation they carry.

The two major categories of pain are nociceptive and neuropathic. This colonoscopy image demonstrates severe colitis that induced visceral nociceptive pain. Nociception is a normal physiologic response to stimuli, initiated by nociceptors that detect mechanical, thermal, or chemical changes. It may be divided into three subtypes. Superficial somatic pain is from cutaneous nociceptors on the skin or superficial tissues. Deep somatic pain is from somatic nociceptors on ligaments, bones, blood vessels, and muscles. Visceral pain is from visceral nociceptors within body organs.

Neuropathic pain is pain induced by damage to the nerves themselves. Herpes zoster (shown) can cause neuropathic pain via growth and inflammation within dermatomal nerves. Hyperpathic symptoms of burning, tingling, or electrical sensations are classic for neuropathic pain. Unfortunately, neuropathic pain is not traditionally responsive to standard pain medications.

Sensitization is an adaptive process in which innocuous stimuli produce an excessive response. Repeated intense stimuli to damaged tissue lower the threshold and frequency of firing of afferent nociceptors. Local inflammatory mediators contribute by recruiting additional nociceptors, which normally remain silent to routine stimuli. For example, patients with bad sunburns will experience severe pain and discomfort to even very light touches because of sensitization of the pain fibers. Sensitization may also be partly responsible in patients with chronic pain syndromes.

This image demonstrates the visceral afferent and modulatory pathways responsible for the pain felt by patients with irritable bowel syndrome. The plus sign denotes pain facilitation and the minus sign denotes pain inhibition. Pain modulation can both enhance and dampen pain signals. Placebo can have a significant analgesic response, and anxiety can magnify the perceived stimuli. Descending signals from the frontal cortex and hypothalamus help modulate the ascending transmission of the pain signal by opiate receptors. (Abbreviations: A6, locus coeruleus; ACC, anterior cingulate cortex; NTS, nucleus tractus solitarius; PAG, periaqueductal gray matter; PFC, prefrontal cortex; RVM, rostra ventral medulla.)

Determining the best treatment course for pain management begins with identification of the intensity and duration of pain. Pain assessment relies largely upon the use of self-report. Both single-dimensional (rating only pain intensity) and multidimensional scales are available. Examples of single-dimensional scales include the Numeric Rating Scale (top) and the Wong-Baker Faces Pain Rating Scale (bottom).^[2]Multidimensional scales, such as the McGill Pain Questionnaire and the Brief Pain Inventory, measure the intensity, the nature and location of the pain, and in some cases, the impact the pain is having on activity or mood. The results obtained from these instruments must be viewed as guides and not absolutes. Image courtesy of the US Department of Veterans Affairs.

Laboratory tests, imaging, and nerve or muscle conduction studies may help identify the root cause of a patient's pain, as well as provide important information about therapeutic planning. For example, the magnetic resonance imaging of a patient with cervical radiculopathy shown here demonstrates a C6-7 disk herniation that is responsible for the patient's pain symptoms. Depending on the extent of the injury, patients may be eligible for injury-specific procedural interventions.

Medical management of pain proceeds in a stepwise fashion, as shown here (based on the "pain ladder" by the World Health Organization). Acute pain is typically treated with short courses of medication therapy, whereas chronic pain may require long-acting medications or other interventional modalities. For mild to moderate pain, nonnarcotic analgesics are used, such as aspirin, acetaminophen, ibuprofen, naproxen, indomethacin, ketorolac, and celecoxib. For moderate to severe pain, narcotic regimens are typically used, including codeine, oxycodone, morphine, hydromorphone, methadone, meperidine, fentanyl, and tramadol. Combination regimens that contain opioids and nonnarcotic analgesics provide additive pain control. Adjuvant medications therapies include tricyclic antidepressants, antihistamines, and anticholinergics.

The pharmacology of pain control is based on influencing one of several biochemical pathways. Many nonnarcotic analgesics inhibit the cyclooxygenase enzyme, which is responsible for the formation of prostaglandin, prostacyclin, and thromboxane. Opiate medications mimic endogenous opioid peptides. Opioids bind to one of three principle classes of opioid receptors (mu, kappa, delta) to produce centrally mediated analgesia. Tricyclic antidepressants are thought to potentiate the effect of opiates. Image courtesy of Wikimedia Commons.

Patient-controlled analgesia allows patients to self-titrate their intravenous pain medication. It allows for a more consistent administration of analgesia with a reduced duration between when the patient feels pain and when analgesia is administered. It reduces the chances for medication errors, reduces nursing workload, increases patient autonomy, and provides objective data about the amount of medication a patient needs. It is traditionally used for postoperative patients and those with serious oncologic or hematologic diseases. Image courtesy of Wikimedia Commons.

Transdermal patches provide controlled drug delivery with a lower potential for abuse than oral analgesics. Patches can be applied once every 12 to 24 hours. Conditions such as postherpetic neuralgia and chronic cancer pain are routinely treated with transdermal patches. Opiate-infused lollipops (shown) and buccal lozenges are other alternative forms of drug delivery used to treat patients with malignant pain. Image courtesy of Wikimedia Commons.

This patient is undergoing a sural nerve block. Regional blocks with therapeutic injections can provide excellent relief for patients with localized pain and inflammation. Depending on the clinical scenario, therapeutic, sympathetic, diagnostic, prognostic, or prophylactic blocks may be used. Therapeutic injections allow for a return to normal function, preventing the development of compensatory injuries. The exact procedural technique is dependent on the nerve involved, but the general principle involves the direct injection of local anesthetic or corticosteroid into the perineural space.

Depending on operator familiarity and the difficulty of accessing injection sites, image guidance may be used for direct visualization. This computed tomography-guided image demonstrates an injection needle in good position in the outer aspect of the neural foramen. Computed tomography, ultrasound, or fluoroscopic guidance allows for more precise needle placement, thus reducing the amount of injected drug and reducing complications. The procedure is especially useful in patients with distorted native anatomy.

Surgical interventions are limited for patients with discrete deficits who fail conservative management. Depending on the location of pain, patients will typically undergo a stepwise treatment course involving noninterventional management before being eligible for invasive therapy. Surgically implanted devices, such as intrathecal pumps and spinal cord stimulators, are available for use on a case-by-case basis. This image shows the spread of opioids in the cerebrospinal fluid via a spinal injection. The rostral spread of intrathecal opioids is thought to be responsible for unwanted effects such as respiratory depression, pruritus, hypotension, nausea, and vomiting. Image courtesy of Wikimedia Commons.

Spinal cord stimulation (SCS, shown) is approved by the FDA for indications including failed back surgery syndrome, chronic painful peripheral neuropathy, multiple sclerosis, complex regional pain syndromes, ostherpetic neuralgia, post-thoracotomy pain, phantom limb pain, intercostal neuralgia, and certain spinal cord injuries. The neurophysiologic mechanisms of SCS are not completely understood. Experimental evidence supports a beneficial SCS effect at the dorsal horn level, whereby the hyperexcitability of wide-dynamic-range neurons is suppressed. Evidence exists for increased levels of GABA release and serotonin and, perhaps, for reduced levels of some excitatory amino acids, such as glutamate and aspartame. Image courtesy of Wikimedia Commons.

Transcutaneous electrical nerve stimulation (TENS) units are adjuvant pain control devices that provide pulsatile electric impulses. The proposed mechanisms by which they reduce pain are presynaptic signal inhibition, endogenous pain control, direct inhibition of abnormally excited nerves, and restoration of afferent inputs. TENS units have been used for low back, arthritic, sympathetically mediated, neurogenic, visceral, and postsurgical pain. Although they are widely used and there is a great deal of anecdotal and observation-based evidence, there is a paucity of randomized controlled trials confirming the effectiveness of TENS units. Image courtesy of Wikimedia Commons.

Chronic, refractory pain is best managed with a multidisciplinary team approach that includes psychology, occupational therapy, physical therapy, vocational rehabilitation, and relaxation training. Patients with chronic pain frequently seek complementary and alternative medicine treatment options as well, including acupuncture (shown), dietary supplements, and hypnosis. A 2012 meta-analysis of 29 randomized controlled trials (17,922 patients) found acupuncture to be superior to both sham acupuncture and standard care for the treatment of different types of chronic pain, suggesting that the effects of acupuncture are more than just placebo effect. Image courtesy of Wikimedia Commons.