Chronic musculoskeletal complaints and chronic daily headache share a bidirectional causal relationship in which patients with either condition are predisposed over time to develop the other one.

This key finding from a large, longitudinal, population-based Norwegian study has importance both for front-line clinicians as well as academic researchers, Dr. Lars J. Stovner observed at the European Headache and Migraine Trust International Congress.

“From a practical point of view, one can say that if one has a patient with one of these common complaints, one should try hard to treat it effectively not only to bring relief to the patient but to prevent the development of the other condition,” said Dr. Stovner of the Norwegian University of Science and Technology, Trondheim.

The new observation of a bidirectional relationship between chronic musculoskeletal pain and chronic daily headache – that is, headache on an average of 15 or more days per month – may also have import in terms of understanding the relevant pathophysiology. It suggests the disorders may share a common underlying cause.

“It says that chronic pain in the body is probably very much related to chronic headache. As we’ve heard elsewhere at this conference, they are both basically brain disorders,” he continued.

Dr. Stovner presented data from two consecutive surveys conducted 11 years apart as part of the Nord-Trondelag Health Study (HUNT). HUNT 2 included 51,383 adults queried in 1995-1997, of whom 26,197 completed the HUNT 3 questions regarding headache and chronic musculoskeletal pain at follow-up in 2006-2008.

Participants with chronic musculoskeletal complaints at baseline in HUNT 2 proved to have a 1.8-fold increased risk of developing chronic daily headache 11 years later in HUNT 3, compared with subjects without baseline chronic musculoskeletal pain in a multivariate analysis adjusted for the known potential confounders of age, gender, anxiety, depression, and socioeconomic status.

Moreover, subjects with chronic daily headache but not chronic musculoskeletal pain in HUNT 2 had an identical adjusted 1.8-fold increased risk of developing chronic musculoskeletal pain in HUNT 3. The risk climbed even higher, to 2.7-fold, when the analysis was restricted to individuals with widespread chronic musculoskeletal complaints in HUNT 3.

“This is a huge population-based prospective study running for longer than 10 years,” commented session cochair Dr. Zaza Katsarava of Evangelist Hospital in Unna, Germany. “The results clearly show there are no separate physiologic baskets for migraine and back pain. They are both part of an entire pain matrix that is impaired.”

Another HUNT analysis Dr. Stovner presented separately at the congress focused on the distinction between medication overuse headache and chronic daily headache without medication overuse. The study population consisted of 25,598 adults with no chronic daily headache in 1995-1997 at HUNT 2. Eleven years later, at the HUNT 3 follow-up, 201 subjects had developed medication overuse headache, for an incidence rate of 0.72 cases per 1,000 person-years.

“I think that’s perhaps a bit lower than would be expected from some of the retrospective studies done before in other countries, which suggest an incidence of medication overuse headache of 1%-1.5% per year,” he noted.

Another 246 subjects developed chronic daily headache without medication overuse.

The key finding in this analysis was that several of the risk factors for development of medication overuse headache were not risk factors for chronic daily headache without medication overuse, indicating that these two disorders are pathogenetically distinct conditions, according to Dr. Stovner.

Shared risk factors for development of the two forms of chronic headache were female gender, having little education, chronic musculoskeletal complaints, insomnia, and headache at baseline.

In contrast, risk factors unique to the development of medication overuse headache included regular use of tranquilizers at baseline, which was associated with a 5.2-fold increased risk; a combination of gastrointestinal complaints, chronic musculoskeletal complaints, and anxiety and/or depression as defined by a Hospital Anxiety and Depression Scale score in excess of 11, which carried a 5-fold risk; smoking, which doubled the risk of subsequent medication overuse headache; and physical inactivity, which also was linked to a 2-fold elevated risk.

The implication of these findings is that the prevention and treatment of medication overuse headache should focus on the treatment of medical and psychiatric comorbid conditions, the use of tranquilizers, and lifestyle changes directed at smoking cessation and increased physical activity, Dr. Stovner concluded.

HUNT is supported by Norwegian governmental research funds. Dr. Stovner reported having no financial conflicts.