Twin study lends new insights into link between back pain and depression

Genetic factors help to explain the commonly found association between low back pain and depression, suggests a large study of twins in the March issue of PAIN®, the official publication of the International Association for the Study of Pain. The journal is published by Wolters Kluwer.

Genetic factors affecting both conditions may be involved in the association between back pain and depression, according to the report by Marina B. Pinheiro, MSc, and colleagues of The University of Sydney, Australia, and Murcia Twin Registry, Spain.

Twin Data Used to Explore Link between Back Pain and Depression

The researchers analyzed data from an established database (Murcia Twin Registry) of nearly 2,150 Spanish twins. Twin studies provide a unique opportunity to elucidate the association between health conditions, by eliminating the genetic and environmental factors contributing to them.

Questionnaire responses were analyzed to determine whether participants with symptoms of depression had higher prevalence of back pain. A series of statistical analyses were then performed to clarify the contributions of genetic factors and early shared environment to the depression-back pain link.

The results showed a significant association between symptoms of depression and low back pain. On initial analysis considering the participants as individuals, rather than twins - and therefore not accounting for genetic and familial factors - the odds of having back pain were about 1.6 higher for those with symptoms of depression and anxiety.

It is not uncommon for those who suffer from chronic pain to feel stressed and depressed at times. This is no surprise, given the fact that "chronic pain" usually means pain that lasts more than three to six months. Prolonged pain appears to set up a pathway in the nervous system that sends pain signals to the brain, even in the absence of an underlying anatomical problem.

Some chronic pain may be due to a diagnosable anatomical problem, such as degenerative disc disease or spinal stenosis, that can cause continual pain until successfully treated. More often, the chronic pain has no clear anatomical cause, as in failed back surgery syndrome or chronic back pain without an identified pain generator. In such cases, the pain is itself the disease.

For some people, the stress and depression resulting from chronic pain can become consuming, and can even worsen and prolong the pain. Increased pain can, in turn, lead to increased stress and depression, creating a cycle of depression and pain that can be difficult to break.

On analysis of twin pairs - which controls for genetic and familial factors that could influence the relationship between depression and back pain - the relationship remained significant, with a 1.7 increase in odds. The association was even stronger - more than a 2.3 increase in odds of low back pain associated with depression and anxiety - on analysis of dizygotic (non-identical) twins, who share half their genes.