Hypertension associated with fewer musculoskeletal complaints

Patients with high blood pressure (BP) have fewer chronic musculoskeletal complaints (MSCs) than those with normal blood pressure, a large-scale population study has found. One explanation for the finding is the phenomenon of hypertension-related hyperalgesia, due to an interaction between the cardiovascular and pain regulatory systems, say the researchers.

The findings, reported in the April 25, 2005 Archives of Internal Medicine, are “remarkably consistent,” say the authors, Dr Knut Hagen and colleagues (Norwegian University of Science and Technology, Trondheim). High systolic (SBP) or diastolic blood pressure (DBP) was associated with a 10% to 60% lower prevalence of musculoskeletal complaints, and there was a strong linear trend (p<0.001) of decreasing prevalence with increasing BP values. The inverse relationship held across all age groups, both sexes, and all 10 anatomical sites at which patients reported feeling pain continuously for at least 3 months in the past year. Asked to comment on this study, Dr Louis Bridges (University of Alabama, Birmingham), who acts as an editorial consultant for jointandbone.org, said: "This is an interesting finding. I had not previously been aware of the reports of inverse association between musculoskeletal complaints and hypertension. The data look solid, but the explanation is unknown. Because there is no obvious pathogenetic link between blood pressure and chronic musculoskeletal pain, I worry that there are unknown confounding factors that may make this finding difficult to replicate in future studies. On the other hand, if a pathogenetic link between BP and musculoskeletal pain were subsequently found, it would lead to a significant paradigm shift. " "At the present time, I do not think that this will change a rheumatologist's approach to treating patients with musculoskeletal complaints," Bridges tells rheumawire.First large-scale population study Hagen et al comment that, to their knowledge, this is the first large-scale population-based study to investigate the relationship between BP and chronic MSCs at various anatomical sites. They analyzed data from 2 consecutive public-health studies, running from 1984 to 1986 (Nord-Trondelag Health Study, HUNT-1) and from 1995 to 1997 (HUNT-2). A total of 46 901 adults participated in both studies.Both studies measured BP, but only HUNT-2 included questions about MSCs. Just over half of the participants (51.4%, n=24 127) reported that they had experienced pain and/or stiffness in muscle and joints continuously for at least 3 months in the past year. These individuals were categorized as having chronic MSCs and were asked to mark the location of the pain on a diagram (eg, neck, shoulders, lower back, ankle/foot, etc). The prevalence of chronic MSCs was estimated using multiple logistic regression. A high systolic BP (SBP >150 mm Hg) measured in the HUNT-1 study was associated with a lower prevalence of chronic MSCs in the HUNT-2 study in all age groups and for each sex. The prevalence of chronic MSCs was 20% to 60% lower at all 10 anatomical locations. The inverse relationship was most marked for pain in the trunk (back, chest, abdomen) but was not significantly different from pain elsewhere, the group reports.The decrease in prevalence of chronic MSCs with increasing systolic BP was almost linear, the researchers comment, and the inverse relationship was seen both in individuals who were taking antihypertensive medication as well as those who were not. However, the highest prevalence of chronic MSCs was found among individuals with a low systolic BP and current use of antihypertensives, and this tendency was present even after adjusting for a significant age difference. The researchers comment that their results suggest that the use of antihypertensives may modify the relationship between hypertension and chronic MSCs, so that those with treated hypertension experience more pain that those in whom it remains untreated. For example, in women with high SBP in HUNT-2, the prevalence of chronic MSCs was higher among those taking antihypertensive agents than among those who were not taking these drugs (prevalence odds ratio 0.82 vs 0.67). They note that a previous study has reported that patients with hypertension report an increase in pain sensitivity during treatment with antihypertensive medication.The findings for diastolic blood pressure showed parallel trends. The prevalence of chronic MSCs tended to be highest among individuals with a low DBP and current use of antihypertensive agents, but no significant interaction was found between the use of these drugs and DBP in relationship to chronic MSCs.Less pain because visiting doctors more often? One simple explanation for the findings could be that the patients with hypertension visited doctors more often and so had all their symptoms better treated than the normotensive individuals. However, this is unlikely, say Hagen et al, because a consistent dose-response relationship was clearly demonstrated among those without the use of antihypertensive medication.The fact that pain was lower at all 10 anatomical sites, where different local mechanisms are involved, suggests a fundamental relationship between BP and pain perception in the central nervous system, the researchers write. Of particular relevance is the finding that the inverse relationship between the 2 extends even into the normotensive range, they add: this suggests that it may reflect some common central mechanism underlying antinociception and cardiovascular regulation rather than a specific effect of hypertension itself. The findings may have important consequences, Hagen et al the researchers comment. As BP had a relatively strong association with chronic MSCs, it could be an important confounding factor in clinical trials and so should be adjusted for. And as antihypertensive medications are so widely used, there should be further study of how they influence pain sensitivity, and individuals in pain should be monitored when they start such therapy. (Source: Arch Intern Med 2005; 165:916-922, J Hypertens 2002; 20:485-491: Joint and Bone: April 2005.)