LAS VEGAS (FRONTLINE MEDICAL NEWS) – Metabolic syndrome is not causally related to hand osteoarthritis, according to data from the Framingham Offspring Study.

The new Framingham analysis, which features rigorous longitudinal follow-up, puts a serious dent in the popular hypothesis that metabolic syndrome is a risk factor for osteoarthritis through the proposed mechanism of systemic inflammation, Ida K. Haugen, MD, said at the World Congress on Osteoarthritis.

“Previous positive findings by other investigators may have been due to cross-sectional study design,” Dr. Haugen said. “As far as we know, this is the first longitudinal study of metabolic syndrome and hand osteoarthritis. Previous studies have mostly focused on knee osteoarthritis. The strength of the current study is the focus on hand osteoarthritis because any associations are less confounded by biomechanical factors like excess body weight.”

In recent years, the growing obesity epidemic and the related phenomenon of the metabolic syndrome have been posited to be the hub around which a variety of chronic diseases orbit, including type 2 diabetes, cardiovascular disease, some cancers, and osteoarthritis. Hand osteoarthritis is the phenotype of osteoarthritis best suited to investigation of whether metabolic syndrome promotes osteoarthritis by creating a systemic inflammatory state. Unlike knee, hip, or ankle osteoarthritis, the obesity that is a core feature of metabolic syndrome doesn’t cause much extra loading of the finger joints, Dr. Haugen explained at the meeting sponsored by the Osteoarthritis Research Society International.

Dr. Haugen , a rheumatologist at Diakonhjemmet Hospital in Oslo, presented an analysis of 1,089 Framingham Offspring Study participants aged 50-75 years at baseline, all free of rheumatoid arthritis and all with baseline hand radiographs. Of those patients, 41% met American Heart Association criteria for metabolic syndrome. In a cross-sectional analysis at baseline, the prevalence of metabolic syndrome in the subgroup with baseline hand osteoarthritis was no different from that in those without the disease.

The focus of the study involved the 785 patients who had both baseline hand radiographs and repeat hand x-rays at 7 years of follow-up. At baseline, 199 of these patients (25%) already had hand osteoarthritis, as defined by two or more interphalangeal joints with Kellgren-Lawrence grade 2-4 findings, and 49 patients had erosive hand osteoarthritis.

In a cross-sectional analysis at baseline, there was no association between metabolic syndrome and hand osteoarthritis. In contrast to the findings in earlier studies by other investigators, metabolic syndrome was actually associated with a significantly reduced risk of erosive hand osteoarthritis. Indeed, in a logistic regression analysis adjusted for age, sex, and body mass index, having metabolic syndrome was associated with a 58% reduction in the risk of prevalent erosive hand osteoarthritis.

During a mean follow-up of 7 years, 26% of patients who were free of hand osteoarthritis at baseline developed the condition. Of those, 8% developed incident erosive hand osteoarthritis. Metabolic syndrome was unrelated to the risk of these conditions.

Moreover, among patients with baseline hand osteoarthritis, there was no association between having metabolic syndrome and worsening Kellgren-Lawrence scores over time.

“We found no dose-response relationship between the number of metabolic syndrome components and the risk of developing hand osteoarthritis during follow-up,” according to the rheumatologist. “Those with all five components present did not have any higher risk of hand osteoarthritis, compared with those with no components.”

When she and her coinvestigators looked at the impact of the individual components of metabolic syndrome, they found a significant association between hypertension and worsening Kellgren-Lawrence scores over time. In an analysis adjusted for age, sex, and body mass index, having hypertension was associated with a 47% increased likelihood of radiographic worsening in patients with hand osteoarthritis at baseline. However, the association between hypertension and incident hand osteoarthritis was weaker and not statistically significant.

Drilling down further, the investigators found a dose-response relationship between the quartile of diastolic blood pressure and the risk of having hand osteoarthritis at baseline. This was not the case for systolic blood pressure, however. The apparent association between hypertension and hand osteoarthritis is worthy of further exploration, Dr. Haugen said.

None of the other elements of the metabolic syndrome showed any relationship with hand osteoarthritis risk.

The Framingham Offspring Study is supported by the National Heart, Lung, and Blood Institute. Dr. Haugen’s involvement was supported by Extrastiftelsen. She reported having no financial conflicts of interest.