Does pain lead to mental illness or is it the other way around?

It’s common knowledge that pain problems and mental illness will affect many of us over the course of our lives [1-4]. Comorbidity between pain and mental illness is often seen in clinical practice and is well established in the literature [5]. But what actually comes first, is it the pain or is it the mental illness? And could it even be that one disease causes the other? It seems reasonable that pain affects the way we feel, for example influences our mood or makes us anxious. Many patients do state that their pain problem made them depressed. But what about the other way around, e.g. could depression lead to pain problems?

In our recent article in European Journal of Pain we tried to shed some light on the questions above by using a large population-based healthcare register [6]. In Sweden we have a unique opportunity to follow patients over time thanks to our personal identity number (PIN). By law, all provided health care has to be registered using the patient’s PIN. Therefore, we were able to follow a large cohort of patients for up to ten years (2007-2016) to investigate the risk of developing mental illness after a first episode of pain, compared to the risk of developing mental illness without a pain history. We also explored the opposite; the risk of developing pain after a first episode of mental illness and we looked into the same relationships between mental illness and fibromyalgia.

We specifically chose to study patients with diagnoses that are common in primary care; back and abdominal pain and depression/anxiety. In addition, we also looked at fibromyalgia, a condition in which the diagnosis often follows several years of pain. We followed roughly 500 000 adult patients visiting either a physician or a physiotherapist (in Sweden, physiotherapy is a first line treatment for patients with back pain) through all levels of care; primary care, specialized care and inpatient care.

To ensure that we studied incident cases (first onset of diagnosis) we excluded all patients with diagnoses in the ICD-10 chapters F (Mental, Behavioral and Neurodevelopmental disorders) and M (Diseases of the musculoskeletal system and connective tissue) three years preceding the study start. This means that patients entering the study had not received any diagnosis of a musculoskeletal- or mental disorder in the years 2004-2006.

So what did we find? As expected, there was an increased risk of developing mental illness after pain compared to patients without pain, but also the opposite was true; there was an increased risk of equal magnitude to develop pain after mental illness compared to those without mental illness.

The incidence rate ratio for developing mental illness after back/abdominal pain was 2.18 (95% CI=2.14-2-22), for developing abdominal/back pain after mental illness it was 2.02 (95% CI=1.98-2.06), for developing mental illness after fibromyalgia it was 4.05 (95% CI=3.58-4.59) and for developing fibromyalgia after mental illness it was 5.54 (95% CI=4.99-6.16) compared to the unexposed population.

It was not in the scope of this study to investigate the mechanisms behind disease development nor can we conclude that these relationships are causal, even though we did adjust the analysis for sex, age and socioeconomic status. Nevertheless, the results make us speculate whether the studied conditions somehow are two sides of the same coin?

Our findings could have clinical implications. When clinicians meet patients seeking medical attention for either pain or mental illness, it is probably a good idea to assess both factors. Early identification of patients at risk for developing, or already having, comorbid mental illness and pain might help to tailor interventions accordingly and hopefully this would have a better treatment effect than if only one condition were targeted.

About Elisabeth Bondesson

Elisabeth is a Physiotherapist who graduated in 1986. Since then, she has been working in inpatient care, primary care and for the last 15 years in pain rehabilitation clinics. Today, she spends her working hours in two ways:  being a national coordinator for the Swedish quality register for pain rehabilitation in primary care and studying for a PhD. Her PhD research looks at comorbidity between pain and mental illness as well as incidence and prevalence of pain among children and adolescents, using register data.

References

[1] Breivik H, Collett B, Ventafridda V, Cohen R, Gallacher D. Survey of chronic pain in Europe: prevalence, impact on daily life, and treatment. European journal of pain (London, England). 2006;10(4):287-333.

[2] Demyttenaere K, Bonnewyn A, Bruffaerts R, Brugha T, De Graaf R, Alonso J. Comorbid painful physical symptoms and depression: prevalence, work loss, and help seeking. Journal of affective disorders. 2006;92(2-3):185-93.

[3] Jordan KP, Kadam UT, Hayward R, Porcheret M, Young C, Croft P. Annual consultation prevalence of regional musculoskeletal problems in primary care: an observational study. BMC musculoskeletal disorders. 2010;11:144.

[4] Stefansson CG. Chapter 5.5: major public health problems – mental ill-health. Scandinavian journal of public health Supplement. 2006;67:87-103.

[5] Bair MJ, Robinson RL, Katon W, Kroenke K. Depression and pain comorbidity: a literature review. Archives of internal medicine. 2003;163(20):2433-45.

[6] Bondesson E, Larrosa Pardo F, Stigmar K, Ringqvist A, Petersson IF, Joud A, et al. Comorbidity between pain and mental illness – Evidence of a bidirectional relationship. European journal of pain (London, England). 2018;22(7):1304-11.