Abstract
Shifting population demographics are resulting in a rapidly growing population age 65 and older. As a result, the majority of providers will be exposed to the older adult in pain. Although pain is a common problem in older adults, it should not be considered a normal part of aging. Chronic pain assessment in the older adult requires an understanding of the complex contributing biopsychosocial factors. Improving quality of life, optimizing functional independence, and managing disability in the older adult should be the goals of all treatments. In cases where independence is not possible, such as in the case of advanced dementia, relying on caregivers to assist with detection of pain and treatment plans is critical. When possible, treatment of pain in the older adult should begin with nonpharmacologic strategies (e.g., exercise, physical therapy, prescription of assistive device) to reduce polypharmacy, drug-drug, and drug disease interactions. Combining nonpharmacologic and pharmacologic treatment approaches to pain should be the next step. Pharmacologic treatments include topical, oral, or injection routes for medication delivery. It is important that providers minimize use of potentially inappropriate medications in older adults due to high risk of adverse effects. Providers should recognize how pain manifests differently in the older adult and utilize treatment strategies that include interdisciplinary and multidisciplinary approaches.
Keywords
aging, drug interactions, geriatrics, interdisciplinary nonpharmacologic and pharmacologic treatment, pain in older adults
It is estimated that the number of individuals aged 65 and older will grow to 1.5 billion by 2050, with 83.7 million older adults in the United States. Given the rapidly changing demographics, the aging population will require the care of physicians from all disciplines; therefore they should be familiar with the unique medical aspects related to the older adult. Advances in health care and improvements in prevention strategies have allowed individuals to live longer with chronic illnesses and functional and cognitive impairments. In older adults, additional factors such as reduced physiologic reserve, polypharmacy, and decreased activity further contribute to this functional and cognitive decline. Understanding how pain presents in the older adult and implementing treatment strategies to reduce pain is critical, but more important is the need to maintain functional independence.
Presentation of Disease/Comorbidity
Chronic pain can be considered a geriatric syndrome, a multifactorial health condition that occurs when the accumulated effects of impairments in multiple systems render the older adult vulnerable to situational challenges. The quest for a unifying diagnosis to explain the presenting signs and symptoms in the older adult with chronic pain often fails, as more often than not there are multiple contributing factors. These include altered biomechanics, sleep and mood disturbances, cognitive deficits, and other chronic comorbidities. For example, the treatment targets in the older adult with fibromyalgia may be weight management through activity and diet, the optimization of sleep and mood rather than direct treatment of the area of pain. Another example is that of the older adult with chronic low back pain (CLBP). A recent series titled “Deconstructing Chronic Low Back Pain in the Older Adult” examined other diagnostic contributors to CLBP that may require a unique treatment approach.
Aging-Associated Physiology and Pathology
Many physiologic changes occur with aging. Medical conditions such as dementia, peripheral neuropathy, osteoporosis, osteoarthritis, and cancer are found more commonly in older adults. The evaluation of older adults with chronic pain requires a working knowledge of how these diagnoses affect evaluation and management decisions. Based on this understanding, the goal of the pain practitioner should be to optimize function when possible and minimize adverse effects when deciding on appropriate treatment plans.
Nervous System
Decreases in short-term memory and cognitive processing speed are known to occur with aging, although cognitive decline widely differs among older adults, with varying degrees of neuronal loss, neurotransmitter changes, and alterations in synapses within the nervous system. The prevalence of dementia increases, with Alzheimer’s disease being the most common form. Current figures suggest that 25% to 30% of people 85 years of age and older have dementia. These individuals may be unable to communicate their source of pain or may fixate on pain itself when the underlying process may be anxiety or fear.
Aging is associated with a decline in the number of myelinated and unmyelinated fibers, an increase in the number of damaged nerve fibers, and slowed nerve conduction velocity, resulting in alterations in proprioception, postural instability, and balance deficits. Peripheral neuropathy is more common in older adults due to comorbidities such as diabetes, chronic kidney disease, and chemotherapy and/or radiation treatments for cancer. In an older adult with cognitive, visual, or hearing deficits, superimposed impairments in proprioception can affect balance adversely, leading to falls in an individual who is already vulnerable. An estimated 30% of adults older than 65 and 50% of adults older than 85 are estimated to have had at least one fall, with more recent evidence suggesting that pain increases this risk. Thus assessment of balance should be a routine part of assessing the older adult with pain.
Musculoskeletal
Sarcopenia is common with advancing age; it is defined as progressive loss of muscle mass associated with muscle cell atrophy and increased fat content. The latter may result in increased retention of fat-soluble medications, which may increase the risk of adverse side effects. There is also a decreased number of motor units. It is estimated that by age 70, there are reductions in the cross-sectional area of skeletal muscle (25%–30%) and muscle strength (30%–40%), which may affect mobility. Decreased muscle strength, decreased range of motion, and common conditions such as degenerative arthritis and osteopenia/osteoporosis may place the older adult at increased risk for falls and resulting fractures. It also should be highlighted that older adults frequently have radiographic evidence of degenerative disease, whether or not they have pain. For example, degenerative disc disease is nearly ubiquitous in older adults ; thus history and physical examination should be the main tools used to identify potential pain generators in those with chronic musculoskeletal pain. Imaging alone should rarely guide management and treatment in the older adult with chronic pain. Older adults often have multiple degenerative musculoskeletal conditions influencing the kinetic chain and leading to additional pathology. For example, older adults with pain associated with knee and hip osteoarthritis may alter their gait and posture, subsequently leading to back pain from altered spine mechanics.
Vision and Hearing
Aging-associated sensory deficits can exacerbate and contribute to pain-related disability. Common eye diseases (e.g., cataract, glaucoma, macular degeneration, and diabetic retinopathy) associated with aging may result in moderate to severe vision loss. Reduced visual acuity, particularly at night, and presbyopia, may predispose the older adult to falls. Poor eyesight may affect how medication is administered or how therapy is performed; for example, use of visual aids such as mirrors or pictures of correct performance of exercises may not be effective. Presbycusis, defined as the loss of hearing with age, is estimated to affect one third of patients over the age of 65 and half over the age of 85. Resulting communication errors may be wide-ranging and include, for example, misunderstanding of pain education delivered by the provider or errors in treatment implementation. Assistive technologies such as hearing aids and a frequency modulation (FM) device for those patients with speech recognition difficulty may be helpful when practitioners evaluate these patients, as they afford the opportunity to engage in more meaningful conversation and improved care.
Drug Metabolism
A number of physiologic changes associated with aging, summarized in Table 41.1 , may lead to alterations in pharmacokinetics and pharmacodynamics. The pain practitioner must be cognizant of these changes to optimize analgesia while also minimizing adverse effects.
| Pharmacokinetics | |||
|---|---|---|---|
| Absorption | Distribution | Metabolism | Elimination |
| Remains unchanged | ↓ Plasma albumin a,b | ↓ Liver volume a,b,c | Measurable and predictable decline in renal function with age a,b |
| ↑ Gastric pH a | ↓ Protein affinity | ↓ Hepatic blood flow a,b,c | ↓ Glomerular filtration rate a |
| ↓ Secretory capacity a | ↑ α 1 -acid glycoprotein a | ↑ Interindividual variability with age a,b | ↓ Renal plasma flow a |
| ↓ GI blood flow a | ↓ Total body water a,b | ↓ First-pass metabolism b | |
| ↑ Expression and activity of P-glycoprotein in liver a | ↓ Phase I metabolism a,c | ||
| ↔ Phase II metabolism a,c | |||
| ↓ Phase II metabolism in frail patients | |||
| Pharmacodynamics | |
|---|---|
| Body Composition | Central Nervous System |
| ↑ Body fat a | ↓ Blood supply to brain a |
| ↓ Lean and total body mass a , b | ↓ Baroreceptor activity a |
| Cardiovascular Function | Renin-Angiotensin-Aldosterone System |
| ↓ Resting heart rate, stroke volume, and cardiac output a | ↓ Plasma renin a |
| ↓ Urine aldosterone a | |
b Pharmacokinetic and/or pharmacodynamic change is accentuated in the frail.
Analgesics Affected by Altered Pharmacokinetics
Medications that have a high hepatic extraction ratio may undergo decreased clearance and experience a longer half-life in older adults because of diminished liver size and blood flow. Meperidine (contraindicated in older adults because of its renally cleared active metabolite that can cause seizures) and morphine are high-extraction-ratio analgesics whose first-pass effect and clearance is reduced with age. The following nonsteroidal antiinflammatory drugs (NSAIDs) with long half lives are hepatically metabolized and their clearance may be reduced in older adults: celecoxib, diflunisal, naproxen, oxaprozin, piroxican, salsalate, and sulindac. The opioids levorphanol and methadone may be similarly affected.
Analgesics that are affected by aging-associated decline in renal function include codeine, duloxetine, gabapentin, meperidine, pregabalin, propoxyphene, salicylate, tramadol, and the opioids morphine, oxycodone, hydromorphone, fentanyl, and methadone. The dosing schedule for gabapentin by renal function is shown in Table 41.5 .
Geriatricians widely use the Cockcroft-Gault equation, shown below, to estimate creatinine clearance (CLcr); it helps to guide the dose adjustment of renally cleared medications:
CLcr = [ ( 140 − age ) × Weight ] [ SCr × 72 ]
Multiply the value by 0.85 for females.
CLcr (mL/min) = creatinine clearance, SCr (mg/dL) = serum creatinine
Age (years), weight (kg)
Analgesics Affected by Altered Pharmacodynamics
Pharmacodynamics refers to tissue sensitivity and how a drug interacts with its end organ. The body’s response to medications may be therapeutic or adverse. The effectiveness of a medication may be influenced by age-related changes in receptors and signal processing—that is, the target organ’s sensitivity. Opioid sensitivity increases with the associated decline in mu opioid receptor density and increase in opioid affinity. Thus older adults may respond to opioid doses that are significantly smaller than those used in younger individuals.
Comprehensive Pain Assessment
Chronic pain assessment in older adults requires comprehensive identification of the multiple contributing biologic, mechanical/physical, social, and psychologic factors. The assessment and monitoring of patient-identified goals should be implemented in all patient encounters. To identify the efficacy of prescribed interventions, it also is critical to identify the meaningful outcomes to be tracked in the course of treatment. Tables 41.2 and 41.3 suggest approaches for assessing pain and offer outcome measures to be followed during pain treatment.
| How strong is your pain (right now, worst/average over past week)? |
| How many days over the past week have you been unable to do what you would like to do because of your pain? |
| Over the past week, how often has pain interfered with your ability to take care of yourself, for example, with bathing, eating, dressing, and going to the toilet? |
| Over the past week, how often has pain interfered with your ability to take care of your home-related chores such as going grocery shopping, preparing meals, paying bills, and driving? |
| How often do you participate in pleasurable activities such as hobbies, socializing with friends, travel? Over the past week, how often has pain interfered with these activities? |
| How often do you do some type of exercise? Over the past week, how often has pain interfered with your ability to exercise? |
| Does pain interfere with your ability to think clearly? |
| Does pain interfere with your appetite? |
| Does pain interfere with your sleep? How often over the past week? |
| Has pain interfered with your energy, mood, personality, or relationships with other people? |
| Over the past week, how often have you taken pain medications? |
| How would you rate your health at the present time? |
| Domain Functional | Parameters | Comments |
|---|---|---|
| Basic and instrumental activities of daily living (ADL, IADL) Mobility/activity level Sleep Appetite Pain intensity | Look at the degree of assistance needed. Decreased activity, such as the diminished participation in advanced activities of daily living (AADL) in the community dweller, or decreased ability to participate in am care in the nursing home resident may indicate pain. Ask about pain awakening from sleep, difficulty falling asleep because of pain, time spent in bed during the day. Many persistent pain patients experience appetite suppression from pain. Follow caloric intake and weight. In nursing home residents, use pain thermometer, behavioral indicators of pain, and rate of prn analgesic ingestion. In community dwellers, use numeric or verbal scales. |
| Mood Interpersonal interactions/behavior | Anxiety and depression may coexist and worsen in patients with pain. Reclusiveness and/or irritability/agitation may occur. In nursing home residents, tone of interactions with staff, family, and other residents may be helpful. |
| Mental status Beliefs and attributions | Consider pain as causative in the patients who experience decline in mental status or delirium. The Mini Mental State Examination may not be sensitive enough to detect subtle changes. Note if the patient has changed orientation from a “fix-me” mentality to a “teach-me” mentality. |
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