Obesity and Pain Management
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
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.