Pain is the most common symptom that brings a patient to a physician’s attention.
Management depends on determining its cause, alleviating triggering and potentiating factors, and providing rapid relief whenever possible.
Pain may be of somatic (skin, joints, muscles), visceral, or neuropathic (injury to nerves, spinal cord pathways, or thalamus) origin. Characteristics of each of the types are summarized below:
- Nociceptive stimulus usually evident
- Usually well localized
- Similar to other somatic pains in pt’s experience
- Relieved by anti-inflammatory or narcotic analgesics
- Most commonly activated by inflammation
- Pain poorly localized and usually referred
- Associated with diffuse discomfort, e.g., nausea, bloating
- Relieved by narcotic analgesics
- No obvious nociceptive stimulus
- Associated evidence of nerve damage, e.g., sensory impairment, weakness
- Unusual, dissimilar from somatic pain, often shooting or electrical quality
- Only partially relieved by narcotic analgesics; may respond to antidepressants or anticonvulsants.
Some Important Terms to Understand:
Neuralgia: pain in the distribution of a single nerve, as in trigeminal neuralgia;
Dysesthesia: spontaneous, unpleasant, abnormal sensation;
Hyperalgesia and hyperesthesia: exaggerated responses to nociceptive or touch stimulus, respectively;
Allodynia: perception of light mechanical stimuli as painful, as when vibration evokes painful sensation.
Reduced pain perception is called hypalgesia or, when absent, analgesia.
Causalgia is continuous severe burning pain with indistinct boundaries and accompanying sympathetic nervous system dysfunction (sweating; vascular, skin, and hair changes—sympathetic dystrophy) that occurs after injury to a peripheral nerve.
Sensitization refers to a lowered threshold for activating primary nociceptors following repeated stimulation in damaged or inflamed tissues; inflammatory mediators play a role. Sensitization contributes to tenderness, soreness, and hyperalgesia (as in sunburn).
Referred pain results from the convergence of sensory inputs from skin and viscera on single spinal neurons that transmit pain signals to the brain. Because of this convergence, input from deep structures is mislocalized to a region of skin innervated by the same spinal segment.
The problem is often difficult to diagnose with certainty, and patients may appear emotionally distraught.
Several factors can cause, perpetuate, or exacerbate chronic pain:
(1) painful disease for which there is no cure (e.g., arthritis, cancer, chronic daily headaches, diabetic neuropathy);
(2) perpetuating factors initiated by a bodily disease that persist after the disease has resolved (e.g., damaged sensory or sympathetic nerves);
(3) psychological conditions. Pay special attention to the medical history and to depression. Major depression is common, treatable, and potentially fatal (suicide).
Acute Somatic Pain
• Mild to moderate pain: Usually treated effectively with nonnarcotic analgesics, e.g., aspirin, acetaminophen, and NSAIDs, which inhibit cyclooxygenase (COX) and, except for acetaminophen, have anti-inflammatory actions, especially at high dosages. Particularly effective for headache and musculoskeletal pain.
• Parenteral NSAIDs: Ketorolac and diclofenac are sufficiently potent and rapid in onset to supplant opioids for many patients with acute severe pain.
• Narcotic analgesics in oral or parenteral form can be used for more severe pain. These are the most effective drugs available; the opioid antagonist naloxone should be readily available when narcotics are used in high doses or in unstable patients.
• Patient-controlled analgesia (PCA) permits infusion of a baseline dose plus self administered boluses (activated by press of a button) as needed to control pain.
• Develop an explicit treatment plan including specific and realistic goals for therapy, e.g., getting a good night’s sleep, being able to go shopping, or returning to work.
• A multidisciplinary approach that utilizes medications, counseling, physical therapy, nerve blocks, and even surgery may be required to improve quality of life.
• Psychological evaluation is key; behaviorally based treatment paradigms are frequently helpful.
• Some patients may require referral to a pain clinic; for others, pharmacologic management alone can provide significant help.
• Tricyclic antidepressants are useful in management of chronic pain from many causes, including headache, diabetic neuropathy, postherpetic neuralgia, chronic low back pain, cancer, and central post-stroke pain.
• Anticonvulsants or antiarrhythmics benefit pts with neuropathic pain (e.g., diabetic neuropathy, trigeminal neuralgia).
• The long-term use of opioids is accepted for pain due to malignant disease, but is controversial for chronic pain of nonmalignant origin.