Boston Medical Center

Pain Sensitization Declines After Bariatric Tx in Obese Patients

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Decreased knee pain linked with central sensitization

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Weight loss following bariatric surgery was associated with improvements in pain sensitization among obese patients with chronic knee pain, a year-long study found.

One year after bariatric surgery, the pressure pain threshold increased by 38.5% at the patella and by 30.9% at the wrist among patients who had undergone either laparoscopic roux-en-y gastric bypass or sleeve gastrectomy, whereas no changes in the pressure pain threshold were observed among patients who had medical/lifestyle management, according to Joshua J. Stafanik, PhD, MSPT, of Northeastern University in Boston, and colleagues.

 “Improvement in pressure point threshold at the wrist suggests that the pain improvement in the surgical subjects was at least in part mediated through central sensitization,” the researchers wrote online in Arthritis Care & Research.

Obese individuals typically report more musculoskeletal pain than do those of normal weight, particularly at the knees, which has been attributed to mechanical stresses from excess loading at the weight-bearing joints and also to the release of adipokines from adipose tissue and the resulting low-grade joint inflammation.

But it has not been established whether additional pain relief at sites beyond the knee is provided by changes in central and peripheral pain sensitization, defined as “increased responsiveness of the peripheral and central nervous systems to nociceptive input,” according to the authors. So they sought to examine this possibility among individuals seen at the Nutrition and Weight Management Center at Boston Medical Center.

They recruited 87 participants who met the eligibility criteria for bariatric surgery, which were a BMI of 35 plus a weight-associated comorbidity, or a BMI >40. They all had knee pain on most days of the previous month.

Those receiving medical management were prescribed a low-fat diet of 1,200 to 1,800 calories per day plus medications such as phentermine, lorcaserin, and bupropion/naltrexone. Exercise, including walking 30 minutes daily, also was encouraged.

Knee pain was evaluated according to the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and pressure pain thresholds were assessed with a hand-held algometer applied at a rate of 0.5 kg/sec to the radioulnar joint and index patella.

The radioulnar joint of the right wrist was considered a control site, as it is not usually affected by osteoarthritis. The researchers also recorded the number of joints other than the knees with frequent pain in the past month.

A lower pressure pain threshold reflects higher sensitivity to pain.

A total of 45 patients in the surgery group and 22 in the medical group completed the 1-year follow-up.

Among the surgery group, mean age was 43.8, 97.8% were women, and baseline BMI was 42.1. Their WOMAC pain score was 9.5 out of 20, and the average number of painful joints was 7.1. The pressure pain thresholds were 346.5 kilopascals at the patella and 335.6 at the wrist.

 In the medical management group, mean age was 48.1, 86.4% were women, and BMI was 40.7. WOMAC pain score was 11.5, mean number of painful joints was 6.3, and pressure pain thresholds were 450.7 and 387.7 at the patella and wrist, respectively.

At 1 year, the mean weight loss in the surgery group was 32.7 kg (about 72 lbs) compared with 4.6 kg in the medical management group.

Mean change in WOMAC pain score from baseline in the surgery group was -4.9, which was statistically significant (P<0.0001), while the -1.5 change in the medical management group was not significant. The change from baseline in number of painful joints was -2.3 in the surgery group (P=0.002), but +0.9 in the medical management group.

At 1 year, the change in pressure point threshold was +133.3 at the patella and +103.8 at the wrist, compared with changes of -56.4 and +44.4 in the medical group.

Changes in weight correlated with differences in WOMAC pain (r=0.50, P<0.0001) and in pressure point threshold at the patella (r=-0.33, P=0.006), although not with changes in pressure point threshold at the wrist (r=-0.04, P=0.77). There also was a moderate inverse correlation between WOMAC pain changes and changes in pressure point thresholds at both patella (r=-0.4, P=0.007) and wrist (r=-0.4, P=0.002).

 The improved pressure point thresholds at the wrist and decrease in number of painful joints support the possibility that central pain sensitization is a mediator of pain reduction in the patients who had bariatric surgery, the authors noted.

“In the presence of sensitization, nociceptors respond to stimuli that they would normally not respond to. However, due to neuroplasticity, removal of the stimuli that contribute to sensitization may normalize nociceptor functioning,” they explained.

They also pointed out that other factors also may contribute to changes in pain after weight loss surgery, such as increased physical activity and improvements in mood and quality of sleep. In addition, further research will be needed to account for the potential influence of inflammatory markers such as C-reactive protein and metabolic factors on pain following bariatric surgery.

C difficile: Obesity Linked to Community-Onset Infections.

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Obesity may be a risk factor for Clostridium difficile infection (CDI), according to results from a retrospective cohort study of 132 cases seen at a tertiary care medical center.

After potential confounders were taken into account, patients with simple community-onset infections were more than 4 times as likely to be obese as patients who had community-onset infections that came shortly after an exposure to a healthcare facility, according to data reported in an article published in the November issue ofEmerging Infectious Diseases.

“Obesity may be associated with CDI, independent of antibacterial drug or health care exposures,” write the researchers, led by Jason Leung, MD, from the University of Michigan Hospital in Ann Arbor. Such an association could help explain the uptick of community-onset cases in individuals having low levels of traditional risk factors.

The authors propose that obesity may perturb the intestinal microbiome in ways similar to those seen with inflammatory bowel disease and use of antibiotics, both of which are known risk factors for CDI.

“Translational research could help elaborate the dimensions of the interaction of the intestinal microbiota with C. difficile in obese patients,” the researchers maintain. They also suggest that an investigation of a dose–response relationship between body mass index and infection risk might be informative.

“[I]t is critical to establish whether obesity is a risk factor for high rates of C. difficile colonization, as is [inflammatory bowel disease]; if that risk factor is established, prospective observations would improve understanding of whether obesity plays a role in the acquisition of CDI, or alters severity of disease and risk for recurrence,” they write.

As for the patients with community-onset infections after healthcare exposure, the study’s findings highlight “the importance of increased infection control at ancillary health care facilities and surveillance for targeting high-risk patients who were recently hospitalized.”

In the study, the researchers reviewed the microbiology results and medical records of all patients who had laboratory-proven, nonrecurrent CDI at Boston Medical Center in Massachusetts during a 6-month period.

When the patients were classified according to the setting of disease onset, 43% had infections that began in the community without recent exposure to a healthcare facility, 30% had infections that began in a healthcare facility, and 23% had infections that began in the community within 30 days of exposure to a healthcare facility (most often a hospital or long-term care facility).

The prevalence of obesity, defined as a body mass index exceeding 30 kg/m2, was 34% in the group with community-onset infections compared with 23% in the general population (odds ratio, 1.7; 95% confidence interval [CI], 1.02 – 2.99). The value stood at 13% in the group with community-onset healthcare-associated infections and 32% in the group with healthcare-onset infections.

In multivariate analyses, patients with simple community-onset infections were significantly less likely to be older than 65 years (odds ratio, 0.35; 95% CI, 0.13 – 0.92; P < .05) and more likely to be obese (odds ratio, 4.06; 95% CI, 1.15 – 14.36; P < .05) than patients with community-onset healthcare-associated infections.

In addition, patients with simple community-onset infections were significantly less likely to have prior antibiotic exposure (odds ratio, 0.29; 95% CI, 0.11 – 0.76; P < .05) than patients with healthcare-onset infections. There was also a trend whereby they were much more likely to have inflammatory bowel disease (odds ratio, 6.40; 95% CI, 0.73 – 56.17; P < .10).

Finally, patients with community-onset healthcare-associated infections were dramatically less likely to have had prior antibiotic exposure than patients with healthcare-onset infections (odds ratio, 0.08; 95% CI, 0.02 – 0.28; P < .05).

Thyroid Screening Neglected in Hypercholesterolemia.

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Just half of primary-care patients with hypercholesterolemia received recommended thyroid-function screening, a new retrospective study has found.

The findings were presented here at the American Association of Clinical Endocrinologists (AACE) 2013 Scientific & Clinical Congress by Devina Willard, MD, an internal-medicine resident at Boston Medical Center, Massachusetts.

Hypothyroidism is an important secondary cause of elevated total cholesterol and LDL cholesterol. In overt hypothyroidism cases, thyroid hormone replacement treatment often normalizes the cholesterol levels. For that reason, guidelines from the AACE, American Thyroid Association, and National Cholesterol Education Program (NCEP) recommend testing for hypothyroidism.

Dr. Willard‘s study was designed to determine the rate of adherence to the guidelines by primary-care physicians. “The 50% rate of screening is a bit surprising. Although guidelines from the NCEP and [American College of Physicians] ACP state that thyroid dysfunction is [included in the] differential [diagnosis] for new-onset dyslipidemia, the practice of screening in standard clinical practice seems to often be overlooked,” she told Medscape Medical News.

Important to Treat Underlying Cause of Hyperlipidemia

Dr. Willard and colleagues reviewed charts from patients aged 18 years and older with total-cholesterol levels of 200 mg/dL and/or LDL-cholesterol levels of 160 mg/dL or above, who were seen at Boston Medical Center’s internal-medicine and family-medicine clinics for routine care during 2003 – 2011. Patients who had previously taken lipid or thyroid medications were excluded.

Of the 8795 patients newly diagnosed with hypercholesterolemia, thyroid-stimulating hormone (TSH) levels had been checked within 6 months of the diagnosis for 49%. Peripheral thyroid-function tests were also done for 18.4% of the patients.

Of the total 4349 patients who had TSH levels screened, 151 had TSH levels greater than 5 mIU/L and 74 had TSH levels over 10 mIU/L. Of these 225 patients (with TSH levels >5), 50.7% received levothyroxine treatment, Dr. Willard reported.

Of those 114 patients treated with levothyroxine, 75.4% did not receive a lipid-lowering agent within 1 year, possibly because correction of their hypothyroidism resulted in improvement of their lipid panel and correction of the dyslipidemia, she said.

The clinical implications of the findings are identifying a treatable cause of dyslipidemia and saving on the potential costs of long-term management of cholesterol-lowering therapy in many individuals, as well as reducing risk for cardiovascular events, Dr. Willard told Medscape Medical News.

She added, “We agree with the guidelines… It is important to treat the underlying and potentially reversible cause of dyslipidemia. However, we would conclude that more research is needed to better assess the cost/benefit effectiveness of having these guidelines be universally adopted.”

Source: medscape.com