Comorbidity between pain and mental illness - Evidence of a bidirectional relationship

BackgroundPain from various locations in the body and mental illness are common and the comorbidity between the two is well-known although the temporal relationship remains to be determined. Our aim was to follow patients over time to study if pain (here dorsalgia/abdominal pain) or fibromyalgia lead to an increased risk of developing mental illness (here depression/anxiety) and/or the reverse, that is whether patients with mental illness have an increased risk to develop pain or fibromyalgia, compared to the rest of the population. MethodsThis prospective cohort study used the Skane Healthcare Register, covering all care in the region of Skane, southern Sweden (population 1.3 million). The cohort included healthcare consultations in primary care, outpatient specialized care and inpatient care between 2007 and 2016 for all patients without prior registered diagnosis of mental illness or pain, aged 18 or older (n=504,365). ResultsThe incidence rate ratio (IRR) for developing mental illness after pain was 2.18 (95% CI=2.14-2.22) compared to without pain. IRR for developing pain after mental illness was 2.02 (95% CI=1.98-2.06) compared to without mental illness. Corresponding IRR for developing mental illness after fibromyalgia was 4.05 (95% CI=3.58-4.59) and for developing fibromyalgia after mental illness 5.54 (95% CI=4.99-6.16). ConclusionsThis study shows a bidirectional influence of similar magnitude of pain and mental illness, respectively. In monitoring patients with pain or mental illness, a focus on both conditions is thus important to develop appropriate, targeted interventions and may increase the likelihood of improved outcomes. SignificanceWe followed a population-based cohort over a period of 10years, including incident cases of both exposure and outcome and found a bidirectional relationship between pain and mental illness. Clinicians need to pay attention on both conditions, in patients seeking care due to mental illness or pain.