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11 Articles in Volume 13, Issue #7
Ask the Expert: Which NSAIDs are Most Selective for COX-1 and COX-2?
Chronic Pain and Depression: Sorting Out Types of Mood Disorders
Chronic Pain and Depression—Why Antidepressants Treat Both
Editor's Memo: Fibromyalgia: Time To Be a Secondary Diagnosis?
Evaluation and Comparison of Online Equianalgesic Opioid Dose Conversion Calculators
History of Pain: A Brief Overview of the 19th and 20th Centuries
Letters To the Editor
Obesity and Pain Management
Pharmaceutical Treatment of Insomnia In Intractable Pain Patients
The Slipping Rib Syndrome: An Overlooked Cause of Abdominal Pain
You Ordered the Urine Drug Test: Now What?

Obesity and Pain Management

The obese patient poses specific clinical challenges for pain specialists, and often presents with related risk factors that directly contribute to chronic pain

Obesity is a growing problem in America, with an increase in adult rates going from 23% in 1994 to 34% in 2008.1 The trend is not only happening here in the United States, but in many other countries in the world including Norway, South Africa, Mexico, and Pakistan.2 The World Health Organization estimates more than 10% of adults worldwide are obese.3 This has been put on their list of global health problems, with obesity serving as a risk factor to various chronic diseases such as coronary artery disease, diabetes, as well as several types of cancer.

Additionally, the American Medical Association officially declared obesity a disease, and not simply a condition. Obese patients also have increased risks of being diagnosed with hypertension, hyperlipidemia, asthma, and arthritis.4

Chronic pain can also be associated with obesity,5 and the financial burden of medical care for these two conditions are enormous public health concerns; costs of obesity are estimated to be well over $100 billion annually while the costs of chronic pain are more than $70 billion in health care expenses, as well as lost productivity.5 Obese patients also are at a 25% increased risk of sustaining a workplace injury (odds ratio 1.25, 95% confidence interval 1.12-1.39; P<0.001).6

The health consequences are also beginning to affect the economic well being of these patients. A Swedish study of obesity showed a 1.4 to 2.4 times increase in sick days in the obese compared to normal weight individuals. They also showed that the use and cost of medications associated with obesity, such as cardiovascular and diabetes medications, were significantly increased in the obese population (P<.001).7

These health problems ultimately affect the lifespan of these patients. In the Framingham heart study conducted from 1948 to 1990, it was shown that those participants who were obese (body mass index [BMI] ≥30 kg/m2) at the age of 40 had a greater than 6-year lower life expectancy than those who were normal weight (BMI <25 kg/m2).8 Table 1 depicts the standard weight status categories for different BMI ranges.

This review article will explore the many different types of painful conditions obese people may experience, and examine treatment recommendations found in the literature. Conditions will include neuropathic, musculoskeletal, migraine, fibromyalgia-associated pain, and postsurgical pain.

Obesity-Related Factors Contributing to Chronic Pain

Sensitivity to pain may be partly due to the pro-inflammatory state of the obese patient. Tumor necrosis factor-α (TNF-α) and intereukin-6 (IL-6) are important chemical mediators in the transmission of pain, owing to anti-inflammatory medication efficacy in analgesia.9 Adipose tissue (loose connective tissue that stores fat) is a major source of inflammatory mediators such as cytokines and chemokines.10 It was shown that markers such as IL-6 and c-reactive protein (CRP) were significantly related to percent of body fat and insulin sensitivity.11

Where a patient’s adipose tissue is distributed throughout their body also is an important factor regarding chronic pain. Metabolic syndrome is a cluster of risk factors including high fasting glucose, triglycerides, blood pressure, and abdominal obesity. These risk factors are related to the development of type 2 diabetes, a disease closely tied to obesity.12

Visceral abdominal adipose tissue is more metabolically active and releases greater amounts of pro-inflammatory and insulin-resistant substances than other adipose tissue.13 Overall, abdominal adipose tissue is an independently strong predictor of risk for developing type 2 diabetes.14 The “Homer Simpson” body type, which embodies heavy abdominal fat, is more dangerous than other body shapes as it is related to a lesser life expectancy, among other outcomes.15 Central adipose tissue also is associated with a higher likelihood of chronic pain independent of other markers of metabolic syndrome.16

Neuropathic Pain

According to Treede et al, neuropathic pain is defined as “pain arising as a direct consequence of a lesion or disease affecting the somatosensory system.”17 Diabetes is a common cause of neuropathic pain and is a disease that is intimately tied to obesity. Up to half of all long-standing patients with diabetes have polyneuropathy, which is a major cause of morbidity and mortality in the obese population.18 The most common mechanism of injury in diabetic patients with polyneuropathy is mechanical stress that goes unnoticed because of loss of peripheral sensation, most commonly in the feet (Table 2).19 Patients will then walk on the injured tissue, further altering the internal structure. Diabetic neuropathy is caused by a variety of mechanisms interplaying together including disturbances in glucose control, insulin, insulin-like growth factor, c-peptide, and structural control of tissues.20

Currently, there are still problems with controlling neuropathic pain. Prevention remains at the heart of treatment, with tight glycemic control in patients with diabetes. Further treatment options include weak opioids and stronger opioids such as hydrocodone and oxycodone; however, treatment should not be limited to these options as it has been shown that anticonvulsants, tricyclic antidepressants, selective serotonin reuptake inhibitors, local anesthetics, and gabapentin are all useful in the treatment of neuropathic pain (Table 3).21,22

In addition to the oral and topical medications mentioned, there is new work being done to investigate different regional blocks and their roles in the treatment of diabetic neuropathy. Cheng et al showed in a case study that sympathetic blocks to the thoracic and lumbar regions provided sustained pain relief for a 37-year-old male who had experienced numbness, tingling, and a cold sensation that began in his feet and spread up to his knees over 3 months before being diagnosed with painful diabetic small-fiber sensory neuropathy.23 This may prove to be a good adjunct to the treatment of painful diabetic neuropathy refractory to first-line medications.

Musculoskeletal Pain

The obese patient commonly has to deal with many musculoskeletal pains. A national study in Australia showed that the odds of having arthritis were 7 times higher for the obese compared to those of normal weight.24 Overweight and obese patients have higher rates of low back and neck pain.25,26 The effects of weight only get worse as the patient’s BMI increases. Patients with obesity were shown to have more pain walking up and down stairs as well as less lower back strength compared to overweight individuals.27 In the past, this pain that resulted from climbing stairs was viewed as a mechanical stress of extra weight on the joints and tissues. However, because pain is still more common in the lower limbs compared to the upper, especially in patients with osteoarthritis (OA), investigators have concluded that increased pain in all areas of the body was getting worse with increasing BMI; thus, pain is likely due to more than just extra weight on the body and has contributing biochemical factors.28,29

Most physicians will prescribe non-steroidal anti-inflammatory drugs (NSAIDs) as their first choice of medication for musculoskeletal pain,30 but perhaps the first-line treatment for pain management in the obese should be weight loss. However, weight loss and exercise can prove challenging in obese patients, which is a topic that will be discussed in more detail in subsequent sections. Meta-analysis of randomized-controlled trials has shown, though, that weight loss of more than 5.1%, with a loss of at least 0.24% per week, will result in an improvement in disability and a reduction in pain.31

Headaches

Headaches are a common problem in the general population; however, they are more common and incapacitating in the obese.32,33 BMI was shown to have a positive correlation with headache frequency in women. When examining cross-sectional analysis of 11 datasets of more than 220,000 women with headache or migraine, a BMI of 20 was shown to be associated with the lowest risk for headache while those who had a BMI of 30 had a 35% increased risk; those women who were morbidly obese with a BMI of 40 were associated with even greater odds, showing an 80% increase for headache.34 Bond et al showed that obese patients who were prone to migraines and who underwent bariatric surgery demonstrated a severe reduction in their headaches after significant reduction in weight.35 Hershey et al studied headaches in the pediatric population, and they showed that higher BMI was associated with higher frequency. In addition, they found that children who decreased their BMI showed reductions in headache frequency at 3- and 6-month interval follow-ups.36

The neuropeptide calcitonin gene-related peptide (CGRP) is important in migraine headaches as increased levels are found in jugular flow during migraine attacks.37 CGRP has also been found to be at higher levels in obese women, providing a possible link between increased BMI and increased migraines.38 Depression and anxiety are also thought to be important co-factors for the relationship of migraines and obesity, as there appears to be a relationship between increased migraine frequency and disability in the obese patient and those who suffer from depression and anxiety.39 It remains to be seen whether this is a casual relationship or whether there is a cause and effect.

Fibromyalgia

Fibromyalgia is part of a syndrome of chronic pain associated with tender points at multiple levels, joint stiffness, and symptoms other than those musculoskeletal in origin including mood disorders, fatigue, and sleep disturbances.40 According to the American College of Rheumatology, the diagnosis is based upon the following diagnostic criteria: a widespread pain index (WPI) ≥7 and a system severity (SS) scale rating ≥5, or WPI 3-6 and SS ≥9. This clinical case definition was revised from the 1990 diagnostic criteria, and does not require a physical or tender point examination.41 Obesity unfavorably affects quality and amount of sleep, strength and flexibility, and pain sensitivity in fibromyalgia patients.42 Cognitive behavioral therapy and other psycholo­gical-based therapies have been shown to have beneficial effects in the treatment of fibromyalgia, including reductions in pain, sleep disturbances, functional statuses, and catastrophizing.43 Fibromyalgia, other pain disorders, and obesity all seem to have a psychological component, giving a possible explanation why antidepressants are part of the therapy for many pain disorders. Obesity and depression have a reciprocal relationship.44

Postsurgical Pain

The increasing prevalence of obesity has led to an increase in obstructive sleep apnea (OSA). Following surgical procedures, patients are often given morphine and other opioid analgesics. These medications decrease both the hypoxic and hypercapnic ventilatory responses, which help control respiration. Because of the potential for respiratory compromise in the obese patient post-surgery, it is crucial that opioid dosing be carefully monitored.45 This leads to difficulty managing patients because there is the potential for respiratory depression, but also the need for adequate pain control.

Patients with OSA have an increased tendency for airway collapse and sleep deprivation. These patients are more vulnerable to the effects of sedatives, opioids, and the potential for respiratory depression.46 These risks led Catley et al to examine potential alternatives. They found higher numbers of OSA with severe hypoxemia soon after surgery in those patients receiving morphine for analgesia compared to those receiving regional analgesia. This interplay between sleep and morphine caused problems in respiration resulting in oxygen desaturation.47 Regional anesthesia might be the preferred method of distributing pain relief when possible in this population.48

Limitations to Pain Treatment

The obese patient undergoes more than just physical and economic consequences; they must also endure emotional and social problems associated with their weight. Emotional and physical factors both play roles in obese patients resisting healthcare. Skin wounds are a common problem with these patients, but it becomes harder for them to take care of themselves as their weight increases. Pressure ulcers, candidiasis, skin tears, incontinence, and lymphedema are problems that occur more commonly in the morbidly obese.49 Patients, families, and health care personnel must be cognizant of weight bias in order to give the best health care possible.

Regarding analgesic medications, NSAIDs are part of the first-line treatment in many pain conditions including musculoskeletal pain and headaches. Although they are over the counter, long-term use can cause gastrointestinal, renal, and cardiovascular side effects and their benefits must be weighed against these side effects.30 In fact, Blower et al verified that there is a strong association between NSAID use and upper gastrointestinal emergency admissions. Additionally, out of 630 emergency upper gastrointestinal admissions to two hospitals in the United Kingdom, blood transfusion requirements were significantly higher (P<0.0001) among patients taking NSAIDs.50

Opioids are a commonly prescribed group of medications to help alleviate pain. The problem with opioid prescriptions in the obese is that opioid pharmacokinetics are more closely related to lean body mass than to total body weight. Obese patients do require higher doses, but not as much as would be suspected based upon weight. This can lead to problems with over or under treatment.51 Physicians need to be careful when dosing to achieve pain control to not over treat because opioid-induced respiratory depression is harder to manage in the obese; this is due to their already increased effort at breathing resulting from increased chest wall weight. Pharmacokinetic data in the obese do not exist for many drugs, so clinicians need to design treatment options with the knowledge that clearance and volume of distribution may be altered in the obese patient.52

Obese patients also were found to have significantly higher risk of complications during spinal anesthesia (P=0.02), largely due to challenges associated with anesthesia administration. Spinal anesthesia in obese patients has been associated with a significantly longer duration of puncture, an increased failure ratio when performed by trainees (almost 50%), and an increased number of bloody punctures.53 This was present even amongst experienced anesthesiologists, but was even more pronounced with trainee anesthesiologists. When administering spinal anesthesia, locating body landmarks are important for the clinician in order to avoid complications. In the obese patients, their landmarks are obscured by adipose tissue. Inexperienced anesthesiologists have high failure rates for locating the correct body landmarks in the obese. This may lead to some patients receiving general rather than spinal anesthesia to avoid these risks; however, general anesthesia comes with its own inherent risks, especially in the obese.53

Weight Loss as Treatment And Prevention

Weight loss is an important part of treatment and prevention for many negative comorbidities associated with obesity, including pain. Exercise has additional benefits other than burning calories. Regular exercise reduces inflammatory molecules such as IL-6 and TNF-α, and increases anti-inflammatory markers IL-4 and IL-10.54 Lumbar strengthening and stabilization exercises have been shown to increase low back strength while reducing low back pain.55 Aquatic exercise has been shown to be effective in functional gains in strength and decreasing OA symptoms.56 For those patients with OA, exercise in the water may be a preferable environment to strengthening while reducing axial loads during a workout.

Weight loss is achieved by obtaining a negative balance of calories based on the numbers of calories in versus calories out. It must be stressed that in addition to exercise programs for weight loss, lower calorie diets are important components in the battle against obesity. Some diets appear to be more effective than others. Findings show that lower carbohydrate diets may be more effective. Replacing carbohydrates with protein is an effective strategy for improving outcomes.57 Calorie-restricted high-protein diets coupled with resistance training appears to be the most effective strategy in obese patients. More weight loss and strength gains were shown with this combination of diet and exercise, as compared to other low-calorie diets differing in the carbohydrate-to-protein ratio or those that excluded resistance training.58

Summary

The obese patient continues to be a difficult patient for clinicians in all fields. With the growing trend of obesity, physicians need to stay up to date on the latest treatment options to best deal with obese patients in the short and long term. In the short-term management of pain in the obese, clinicians have to be current on the risks associated with the commonly used modalities. The best long-term strategy for pain management in the obese is weight loss. It is important that patients not only diet with low calorie foods but also undergo strengthening exercises in order to ensure greater weight loss.58 Exercise and dietary weight loss are more effective in combination than when either is done alone.59

As a last resort, bariatric surgery may be beneficial as a weight loss strategy in the morbidly obese. Patients experience relief from pain after significant weight loss (P<0.05) from bariatric surgery. In a study evaluating the effects of bariatric surgery weight loss on knee pain in patients with OA of the knee, patients were evaluated using the Western Ontario and McMaster Universities (WOMAC) Index of Osteoarthritis and the Knee Osteoarthritis Outcome Score (KOOS). The WOMAC targets symptoms of pain, stiffness, and physical function. The KOOS assesses the development or progression of knee osteoarthritis. At 6 and 12 months, all variables from both assessments were significantly improved when compared to baseline (P<0.05).60

The fight against obesity needs to start with education at younger ages. It becomes harder to break habits when neural connections are made as children age and obesity is more likely to follow children into adulthood if they are severely overweight at preteen and teen ages.61,62 Exercise and proper diet need to be taught in all economic levels but especially the lower class as BMI is inversely related to education level and occupational class in industrialized nations.63 Perhaps teaching lower socioeconomic children about healthy living might make it easier for them to avoid the economic hardships that come with obesity. Pain management in the obese can best be achieved in all societal groups with exercise and proper diet as well as properly educating trained clinicians in all fields of medicine.

Last updated on: August 10, 2017
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