CHAPTER 19—PERSISTENT PAIN
ASSESSING AND TREATING PAIN IN COGNITIVELY IMPAIRED PERSONS
Pain, defined as an unpleasant sensory and emotional experience, is common in older persons aged 65 and older. Studies have revealed that 25% to 50% of community-dwelling older adults and 45% to 80% of nursing-home residents have substantial pain. It is also believed to be commonly undertreated. This is due to several factors: some older adults tend to minimize or not report their symptoms, and others are unable to report their pain because of language or cognitive impairments. Also, clinicians may inadequately assess pain or undertreat it with ineffective therapies or encounter intolerable adverse effects with more effective therapies. This chapter describes the evaluation and treatment of persistent pain. Chronic or persistent pain, in contrast to acute pain, is pain lasting 3 to 6 months or more after the original injury has healed, pain that is associated with a chronic medical condition, or pain that recurs at intervals of a month to years.
Persistent pain is complex, involving an amalgamation of physical, social, and psychologic factors. Untreated, it can result in difficulty performing activities of daily living, cognitive dysfunction, depression, anxiety, social isolation, appetite impairment, and sleep disorders. Lastly, patients with chronic pain accrue greater health care costs than do patients who are pain-free.
A major barrier to effective pain treatment is inadequate assessment. A thorough assessment is necessary to formulate a plan to successfully treat persistent pain. This assessment should include an examination of physical, emotional, and social function, recognizing the considerable impact that each of these domains has on the experience of pain and suffering. Since there are no blood tests or imaging modalities to measure pain objectively, clinicians must rely on the patient’s or caregiver’s description of the pain and on the findings of a thorough physical examination. The goal of the assessment is to identify the source of the pain so that it can be treated with the most effective, targeted, and specific treatment known. The evaluation of older persons is complicated by several challenges, including under-reporting of symptoms by many older persons, the existence of multiple medical comorbidities exacerbating the pain and impairing the function of the patient, and the increased prevalence of cognitive impairment as people age.
Initial evaluation begins with a complete history of the pain, including inquiry about the character of the pain, the course of its onset, its duration, and its location. Patients should be asked what relieves and exacerbates their pain. The patient’s functional status needs to be carefully evaluated to determine his or her ability to perform activities of daily living and instrumental activities of daily living. The patient’s cognitive state, participation in social activities, mood, and quality of life are all components of a complete evaluation.
Pain intensity can be quantified using pain intensity scales. Three commonly used validated scales are the Numeric Rating Scale, the Faces Pain Scale, and the Verbal Descriptor Scale. These scales are referred to as unidimensional because they ask the patient to rate the intensity of a single characteristic of the symptom, in this case the intensity of the pain. The patient is asked to rate his or her pain by assigning a numerical value (with zero indicating no pain and 10 representing the worst pain imaginable), a verbal description (“no pain” to “pain as bad as it could be”), or a facial expression corresponding to the pain. The choice of scale depends on the presence of a particular language or sensory impairment. For example, if the patient does not speak English well, the faces scale may be the best choice because it relies on pictures rather than words or numbers. The same scale should be used at follow-up examinations to evaluate how the pain has changed since the initial assessment. Scales such as the McGill Pain Questionnaire and the Pain Disability Scale measure pain in a variety of domains, including the intensity, location, and affect. Although long, scales measuring multiple domains can provide a wealth of information about the patient’s unique experience of pain.
Before the physical examination, the patient can describe the location of the pain using a drawing of a human figure, called a pain map. The patient is asked to indicate the locations on the figure that corresponds to their own pain. Pain maps can enhance patient-clinician communication. If the patient’s pain pattern is erratic and diffuse and therefore nonsensical anatomically, referral to a mental health specialist may be appropriate.
The physical examination should include a careful examination of the reported site of the pain and any part of the body that may be a source of referred pain. Experts suggest that the initial evaluation should include a complete musculoskeletal examination, recognizing the common finding of a musculoskeletal disorder such as fibromyalgia, osteoarthritis, and myofascial pain as either the primary source of pain or an exacerbating process. Accurate diagnosis of these disorders is a critical part of formulating the correct therapeutic plan (see the section, below, on treatment). Fibromyalgia is an under-recognized but not uncommon disorder in older adults. It is typically characterized by multiple tender points, sleep disturbance, fatigue, generalized pain (often with a strong axial component), and morning stiffness. (See also the section on fibromyalgia in Musculoskeletal Diseases and Disorders.) Myofascial pain is present in the vast majority of patients with persistent pain and is diagnosed by the presence of taut bands of muscles and trigger points (ie, pain that may radiate distally upon application of firm pressure to a muscle, as opposed to tender points, in which radiation of pain is absent).
Pain syndromes can be divided into at least three types: nociceptive, neuropathic, and mixed or unspecified. Nociceptive pain describes pain due to the activation of nociceptive sensory receptors by noxious stimuli resulting from inflammation, swelling, and injury to tissues. It can be defined further as either somatic or visceral pain. Somatic pain is well localized in skin, soft tissue, and bone. It is commonly described as throbbing, aching, and stabbing. Visceral pain, due to cardiac, gastrointestinal, and lung injury, is not well localized and difficult to describe. Patients describe visceral pain as crampy, tearing, dull, and aching. Neuropathic pain derives from the irritation of components of the central or peripheral nervous system. Patients typically report burning, numbness with “pins and needles” sensations, and shooting pains. Common causes of neuropathic pain include post-herpetic neuralgia, post-stroke central pain, and phantom limb pain experienced following amputation. Nociceptive pain is often adequately treated with common analgesics. Neuropathic pain responds unpredictably to opioid analgesia; it may respond well to nonopioid therapies such as anticonvulsants, tricyclic antidepressants (TCAs), and antiarrhythmic medications. Confusion between neuropathic pain and myofascial pain is possible, as patients may describe both as “burning.” Careful physical examination will help to differentiate these disorders (ie, taut bands and trigger points with myofascial pain and allodynia or hyperalgesia with either disorder), although both may exist in the same patient. Mixed or unspecified pain is described as having characteristics of both nociceptive pain and neuropathic pain. An example of a mixed pain syndrome is chronic headaches of unknown causes. It may be necessary to treat these patients with trials of different medications or with combinations of medicines. Older adults often have mixed pain syndromes. Lower back pain, for example, is often a combination of spinal malalignment, myofascial pathology, and neurologic impingement.
While they are able to speak, patients with mild to moderate dementia are often able to self-report pain and localize it. Patients with severe cognitive impairment who are unable to verbally express pain pose a challenge to the clinicians who care for them. Not only are they unable to describe the pain and request analgesia, but clinicians are hesitant to administer pain medications, fearing that drugs will worsen the patients’ mental status. Clinicians must rely on observing the patient for possible pain-related behaviors as well as observations noted by the patient’s caregivers. Table 19.1 lists common pain behaviors in cognitively impaired older adults. Validated scales such as the Hurley Discomfort Scale and the Checklist of Nonverbal Pain Indicators have been developed; however, these require trained evaluators to complete properly. Experts suggest providing empiric analgesic therapy during procedures and conditions known to be painful. Trials of analgesia should also be considered for patients exhibiting pain-related behaviors.
A comprehensive review of nonpharmacologic therapies for persistent pain is beyond the scope of this chapter; however, specific therapies are worth mentioning. Many of the strategies mentioned below are appropriate suggestions for all patients’ treatment plans.
Patient education and involvement in treatment decisions are an important part of all treatment plans for persistent pain. Patients should be taught how to take medications properly and how to use assessment instruments. They can be given information on the use of nonpharmacologic treatments such as heat and cold application, massage therapy, and transcutaneous electrical nerve stimulation. Cognitive behavioral therapy may be particularly useful in helping patients learn to cope with the stresses of persistent pain. When possible, family members and caregivers should be included in the therapy.
Regular physical activity has been shown to improve mood, boost functional status, and stabilize gait. Referral to the Arthritis Foundation or community resources such as the YMCA for exercise classes can be considered for many patients. Others who are frail may require closely monitored rehabilitation services. The goals should include improvements in flexibility, strength, endurance, and function, with reduction in pain and improved quality of life.
Patients with persistent pain that do not respond to first-line treatment efforts should, if possible, be referred to a pain clinic that is geared toward interdisciplinary team treatment. Suboptimal treatment response should not be viewed as a permanent state, but as an opportunity for input from specialists who have additional expertise in treating these difficult problems.
See also Complementary and Alternative Medicine.
Individual analgesics, with their starting doses and common adverse effects, are listed in Table 19.2.
Pharmacologic therapy for patients with persistent pain should be viewed not as an end, but as a means to promote improved function and enhance adherence with rehabilitation efforts. When initiating pharmacologic therapy in older adults, it is important to consider the balance of risks and benefits of the treatment. If appropriate, nonsystemic therapies should be tried first. For example, patients that primarily have knee pain might respond to intra-articular corticosteroid injections, avoiding the need for systemic analgesics. Patients with myofascial pain often respond to local modalities such as massage, gentle stretching exercises, ultrasound, and trigger-point injections. Topical preparations such as capsaicin or ketamine gelOL or lidocaine patches might be effective as primary or adjunctive therapy in the treatment of patients with neuropathic or myofascial pain syndromes. If these modalities are ineffective and a decision is made to begin systemic therapy, patients will need to be monitored closely to ensure that the treatment is effective and adverse effects are minimized. Choice of initial dose and rate of titration depends on the individual patient’s physiology, which varies considerably in older persons. As a general rule, when starting opioid therapy it is prudent to start with the lowest dose possible and to titrate slowly. That said, patients who are in a pain crisis should not have medications withheld. Rather, they need to be monitored closely to ensure that the dose can be safely and adequately escalated.
Mild to moderate pain can commonly be treated with acetaminophen or cautious use of nonsteroidal anti-inflammatory drugs (NSAIDs). Acetaminophen has been shown to provide adequate analgesia for many mild to moderate pain syndromes, particularly musculoskeletal pain. No more than 4 g of acetaminophen every 24 hours should be administered to patients with normal hepatic and renal function, given the risk of hepatotoxicity. Caution should be taken with treating patients at risk for liver dysfunction, particularly those who have a history of heavy alcohol intake. In these patients, the dose should be lowered by 50%, or acetaminophen should be avoided. Because acetaminophen is commonly contained in many over-the-counter and prescription products, knowledge of all medications that a patient is taking is critical to avoiding acetaminophen toxicity. NSAIDs are effective drugs for the treatment of mild to moderate pain and may be useful when acute exacerbations of pain are not controlled with acetaminophen. However, significant adverse effects, including renal dysfunction, gastrointestinal (GI) bleeding, platelet dysfunction, fluid retention, and precipitation of delirium limit their use in the treatment of older persons’ chronic pain. COX-2 inhibitors were developed to decrease the risk of GI bleeding by acting on a more selective receptor, but the risk for renal complications, including hypertension, remains the same as with other NSAIDs, and the degree to which longer term GI toxicity is reduced is not clear. Several studies have confirmed high cardiovascular risks associated with COX-2 inhibitors, which is now believed to be a class effect. Though one is currently still on the market, the COX-2s certainly should be considered with caution if at all in older individuals. Misoprostol, a prostaglandin analog, or a proton-pump inhibitor may be used to reduce the risk of NSAID-induced GI bleeding, but this does not reduce the risks of renal disease, hypertension, fluid retention, or delirium. Alternatively, nonacetylated salicylates such as salsalate and trisalicylate may have less renal toxicity and antiplatelet activity than other NSAIDs and therefore may be preferable in older persons, though evidence supporting this theory is sparse.
Moderate to severe pain or pain that requires chronic treatment often requires opioid medications to provide sufficient relief. In general, continuous pain should be treated with 24-hour pain medications in long-acting or sustained-release formulations after opioid requirements are estimated on the basis of an initial trial of a short-acting agent. These may be combined with fast-onset medications with short half-lives to cover breakthrough pain. A typical patient requires approximately 5% to 15% the daily dose offered every 2 hours orally for breakthrough pain. In general, different opioids provide similar analgesic efficacy. Cost and route of delivery can help guide the choice of medication.
Opioids are metabolized by the liver and excreted by the kidney. In kidney failure, the active metabolites of morphine, including morphine-6-glucuronide and morphine-3-glucuronide, can accumulate, which places the patient at increased risk for prolonged sedation. The dosing intervals should be increased or the dose lowered to reduce this risk. Some experts and limited data suggest that oxycodone is safer in kidney failure because its metabolism results in fewer active metabolites, but this remains controversial.
Older persons may have concerns about addiction and tolerance that keep them from accepting adequate treatment for their pain. Patients may fear that taking opioid therapy for their current level of pain will result in the pain medicines’ losing their effectiveness in the future when pain becomes more severe. They may fear addiction to the medicines. In fact, fear of addiction is a major obstacle to prescribing medications to older adults. A frank discussion of these concerns may help to alleviate these fears.
Physical dependence is an expected change in a patient’s physiology that occurs while a patient is receiving chronic, continuous opioid medications. If opioids are discontinued suddenly, a patient who is physically dependent will experience a withdrawal syndrome that may include restlessness, tachycardia, hypertension, fever, tremors, and lacrimation. Symptoms of withdrawal can be avoided by tapering opioids carefully over days to weeks. Tolerance refers to a change in physiology resulting in the need to increase opioid medicines over time to achieve adequate analgesic effect. Experts note that tolerance to analgesia, as opposed to tolerance to sedation and respiratory depression, develops slowly in stable disease. If a rapid titration of medicines is required to reduce pain, the cause of the pain should be evaluated, including searching for new pathologies and exacerbation of known sources of pain, as well as consideration of nonphysical factors. Of note, there is limited cross-tolerance between different opioids. Therefore, when switching a patient from one opioid to another (eg, morphine to oxycodone), the clinician should reduce the dose to 50% to 65% of the equivalent dose.
Psychological dependence, or true addiction, refers to a psychiatric state defined by compulsive drug seeking and drug using with disregard for adverse social, physical, and economic consequences. It is very rare for patients who have chronic pain to become addicted to opioids. Addiction must be distinguished from pseudo-addiction, which refers to a patient with significant unrelieved pain who adopts behaviors similar to those of truly addicted patients while seeking relief from suffering, but generally with less prominent disregard for adverse social, physical, and economic consequences.
The most common adverse effect of opioid treatment is constipation. Opioid-induced constipation is due to multiple mechanisms, including dehydration, decreased GI tract secretions, and decreased motility of the GI tract. Although tolerance develops fairly rapidly to other adverse effects of opioids, such as respiratory depression and sedation, constipation usually complicates opioid use for the duration of treatment. Therefore, education regarding the probable need for a laxative is recommended for all patients at the time opioid therapy is initiated. Many experts recommend starting therapy with a stimulant laxative (such as bisacodyl or senna); however, these should be avoided in any patient with signs or symptoms of bowel obstruction. Bulking agents such as fiber and psyllium should be avoided in patients who are inactive and who have poor oral intake, given the risk of causing stool impaction and obstruction. All patients should be encouraged to exercise, as they are able, and to stay well hydrated.
Nausea and vomiting are common side effects of opioids. They have a direct effect on the part of the brain associated with the sensation of vomiting called the chemoreceptor trigger zone. Other common causes of nausea and vomiting in patients taking opioids include gastroparesis, constipation, and metabolic disorders such as renal and hepatic failure. Although the nausea and vomiting is usually self-limited to the first few doses, some patients experience chronic nausea. After evaluation for reversible causes of nausea such as constipation, some patients benefit from changing to an alternative opioid. Others may need to be treated with chronic antiemetics, accepting the high prevalence of adverse effects in older adults treated with these medications, including drowsiness, delirium, and anticholinergic effects.
Older persons may experience sedation, fatigue, and mild cognitive impairment with opioid treatment. These changes commonly occur during dose adjustment. Patients commonly overcome the fatigue and sedation over days to weeks as they become tolerant to the medication. They need to be warned of the risks of increased falls and asked not to drive or operate heavy equipment when the medication is initiated. A small subset of patients treated with opioids experience incessant fatigue that limits their function significantly. A limited course of a stimulant such as low-dose methylphenidate could reasonably be tried in this situation. Rotation to a different opioid is an alternative strategy used to alleviate opioid-induced fatigue.
Respiratory depression is a feared complication of opioid therapy. Older persons and persons with a history of lung dysfunction are at particular risk when opioid doses are increased too rapidly. Naloxone, an opioid receptor antagonist, can reverse opioid-induced respiratory depression; however, when it is given to a patient who has been treated chronically with opioids, it can precipitate a pain crisis and acute withdrawal symptoms. Experts suggest withholding naloxone unless the patient’s respiratory rate decreases to less than 8 breaths per minute or the oxygen saturation drops to below 90%. When it is needed, naloxone should be titrated carefully, using the lowest dose possible.
Nonopioid or adjuvant medications can be used as the sole agent or in combination with opioids. These medications may be particularly useful in treating patients with neuropathic pain or mixed pain syndromes.
Tricyclic antidepressants (TCAs) are the most extensively studied medications for neuropathic pain, though none of the TCAs has been approved for the treatment of pain. Their efficacy in the treatment of post-herpetic neuralgia and diabetic neuropathy has been exhibited in numerous placebo-controlled studies. However, they are associated with significant anticholinergic adverse effects in older persons, including constipation, urinary retention, dry mouth, cognitive impairment, tachycardia, and blurred vision. Of note, desipramineOL and nortriptylineOL may have fewer adverse effects than amitriptylineOL.
Clinical depression in patients with persistent pain requires treatment to effect optimal analgesia and quality of life. Other classes of antidepressants (eg, selective serotonin-reupake inhibitors) have generally been less studied than TCAs as analgesics, but older adults typically tolerate these agents better than TCAs when they are used in antidepressant doses. Duloxetine, an inhibitor of norepinephrine and serotonin uptake, is approved as both an antidepressant and for the treatment of pain from diabetic neuropathy.
Antiepileptic drugs such as carbamazepine (approved for some types of neuropathic pain), gabapentin, and clonazepamOL are commonly used as treatments for neuropathic pain. Gabapentin has demonstrated clinical efficacy in the treatment of post-herpetic neuralgia, and it has considerably fewer adverse effects than TCAs, though its cost is substantially more. The main side effects of gabapentin are sedation and dizziness, which frequently limit dose escalation.
Corticosteroids are useful adjuvants to treat pain associated with swelling, inflammation, and tissue infiltration, as well as neuropathic pain. In addition to their analgesic properties, they also may increase appetite and improve energy. Adverse effects occurring with short-term use of steroids include psychosis, fluid retention, hair loss, loss of skin integrity, hyperglycemia, and immunosuppression. Intravenous bisphosphonates may substantially reduce pain from malignant bone metastases.
Several medications should not be administered to older persons. Propoxyphene (Darvon) is an older opioid medication used to treat mild to moderate pain. However, research and clinical experience has shown that the drug may accumulate in older persons and cause ataxia and dizziness as well as tremulousness and seizures. It has also never been shown to be more a more effective analgesic than placebo. Meperidine (Demerol) is metabolized to normeperidine, a substance that has no analgesic properties but that can accumulate in patients with decreased kidney function and cause tremulousness, myoclonus, and seizures. Neither of these medications is recommended for use in older persons.
Tramadol (Ultram) has combined mechanisms of opioid-receptor binding and norepinephrine- and serotonin-reuptake inhibition. It can lower the seizure threshold and is therefore not recommended for patients with a history of seizures or taking other medications that could lower the seizure threshold. Caution should also be exercised in patients taking other medications with serotonergic properties to avoid serotonin syndrome (myoclonus, agitation, abdominal cramping, hyperpyrexia, hypertension, and potentially death).
Mixed agonist-antagonists such as nalbuphine and butorphanol also have the potential to cause restlessness and tremulousness and therefore should be avoided in older persons. Because of high risks of GI and renal toxicity and substantial risk of delirium in older individuals, NSAIDs should be used cautiously. As mentioned previously, COX-2 inhibitors have been shown to increase the risk of cardiovascular events, in addition to the risks associated with the nonselective NSAIDs.
■ AGS Panel on Persistent Pain in Older Persons. The management of persistent pain in older persons. J Am Geriatr Soc. 2002;50(6 Suppl): S205–S224.
The American Geriatrics Society gathered a multidisciplinary panel of experts in the treatment of older persons’ pain to create a thorough guideline describing the current standard of care. The contributors discuss the epidemiology, assessment, and treatment of pain in the geriatric population. This is a key resource for anyone who cares for geriatric patients.
■ Weiner DK, Herr K, Rudy TE. Persistent Pain in Older Persons: An Interdisciplinary Guide for Treatment. New York: Springer Publishing Company; 2002.
This book is a valuable resource for clinicians of all disciplines who care for older patients. The sections describing the assessment and effects of pain are particularly comprehensive. The authors argue that the impact of pain, both physical and psychological, is greater in individuals who are already frail. Changes that can occur with aging such as cognitive decline, musculoskeletal disease, altered drug metabolism, and functional decline provide specific challenges to clinicians. The authors include effective and practical strategies to address and manage these issues relevant to the care of aging patients. Included in this book are sample questions for a pain interview and a helpful algorithm for the assessment of pain in elderly persons with severe cognitive impairment.
Jennifer M. Kapo, MD
Debra K. Weiner, MD