Chronic pain is frequently described as an intractable pain that does not serve an adaptive purpose (i.e. alerting the organism to danger and/or injury), often lasting longer than six months with no identifiable medical explanation, commonly localized to the lower back, knee joints, head, and neck^1-3.

Traditionally, chronic pain was characterized by the length of time the pain persisted; however, more recent conceptualizations have introduced other concessions. For example, the International Association for the Study of Pain defines chronic pain as being “without biological value … persist[ing] beyond the normal tissue healing time … as determined by common medical experience [and/or] a persistent pain that is not amenable, as a rule, to treatments based upon specific remedies.” ¹

Notwithstanding the foregoing updates in the definition of chronic pain, the manifestation and experience of pain is variable and still does not capture the varieties of chronic pain wherein some forms may display remission and recurrence (e.g., migraine headaches) while others are more likely to be progressive (e.g., rheumatoid arthritis).

Historically, medically unexplained pain was attributed to psychopathology; however, recent evidence suggests that significant alterations to the peripheral and central processing of afferent input, as a consequence of neuroplastic changes resulting from injury or disease processes, contribute to aberrant nociceptive response properties in both the periphery and central nervous system. These subsequently elicit pain in conditions such as fibromyalgia¹.

The subjective experience of pain has been associated with debilitating consequences including cognitive impairment, psychological stress, and social isolation⁴. The prolonged experience of the foregoing constellation of derivative consequences of chronic pain may act as a prodrome to mental illness, notably major depressive disorder.

Interestingly, the determinants of chronic pain largely resemble those associated with major depressive disorder (e.g. age, gender and social economic status)¹. The latter observation is further supported by reports from the World Health Organization indicating that the twelve month prevalence of chronic pain is approximately 37% in developed nations as compared to 41% in developing nations^{1, 5}.

The number of undetected cases of major depressive disorders among individuals presenting with chronic pain as the primary concern is increasingly recognized as a barrier to the appropriate identification, diagnosis, and treatment of this highly prevalent mood disorder⁴. This is particularly worrisome with available evidence suggesting that comorbid pain and depressive symptomatology are associated with a higher rate of antidepressant switching, which is reported to have a negative impact on likelihood of recovery with each subsequent failed treatment ^6-9.

In order to address concerns of the aforementioned barrier to mood disorder diagnosis, a recent review aimed to identify whether any screening tools were available to evaluate both pain and depression and sought to further delineate methods of identifying comorbid depression and pain in a primary care setting.

Results returned a dearth of data on studies using a general screening tool capable of effectively assessing both depressive symptomatology and chronic pain; further research indicated that a validated screening metric investigating both symptoms of depression and pain does not currently exist. An oddity considering the high degree of overlap between chronic pain and mood disorders commonly encountered by physicians.

Consequently, the authors evaluated currently available screening tools for depression and chronic pain independently. They noted that, although a number of screening tools for pain are currently available , the majority are specifically validated to identify certain types of pain (e.g., neuropathic, back pain, knee pain)⁴. 

Taken together, the authors suggested that the most relevant screening tool that could be repurposed to explore the presence of depressive symptoms in individuals with chronic pain was via the National Institute for Health and Care Excellence (NICE) guidelines for identifying chronic physical health problems in primary care. These guidelines recommend that all patients are asked two standard questions about depression, prompting further questioning if either elicit a positive response.

Similar to major depressive disorder, anxiety has also been documented to exhibit high comorbidity with chronic pain and vice versa. For example, data on lifetime prevalence of panic disorder, agoraphobia, social anxiety disorder, generalized anxiety disorder, or post-traumatic stress disorder suggest a 2 to 3-fold increase in individuals who experience chronic pain, especially when localized to the lower back or neck¹⁰.  

It has been hypothesized that the relationship between anxiety and chronic pain are, at least partially subserved by physiological arousal (e.g. increased muscular tension and blood flow, elevated blood pressure and heart rate) wherein prolonged arousal and the activation of inter-related neural and hormonal processes (e.g. cytokine release) contribute to detrimental effects on muscle, bone, and neural tissue over time, due to chronic activation of the stress response.

In keeping with the foregoing observations, and despite significant advances in the understanding of the pathophysiology of persistent pain, its management and treatment – particularly among individuals with mental illness – have not significantly improved.

In an increasingly aging population, the prevalence of chronic pain will continue to increase, resulting in poorer clinical prognosis of both pain and mood/anxiety, increased likelihood of treatment resistance, and additional health service costs^{4, 11}. Taken together, these observations provide the impetus to identify screening tools and potential mechanisms for moderating/mediating chronic pain as a priority research vista.

References 

1. Katz J, Rosenbloom BN, Fashler S. Chronic Pain, Psychopathology, and DSM-5 Somatic Symptom Disorder. Can J Psychiatry 2015;60(4):160-167.

2. Schopflocher D, Taenzer P, Jovey R. The prevalence of chronic pain in Canada. Pain Res Manag 2011;16(6):445-450.

3. Johannes CB, Le TK, Zhou X, Johnston JA, Dworkin RH. The prevalence of chronic pain in United States adults: results of an Internet-based survey. J Pain 2010;11(11):1230-1239.

4. Cocksedge Karen SRSC. Depression and pain: the need for a new screening tool. Progress in Neurology and Psychiatry 2016;26-31.

5. Tsang A, Von KM, Lee S et al. Common chronic pain conditions in developed and developing countries: gender and age differences and comorbidity with depression-anxiety disorders. J Pain 2008;9(10):883-891.

6. McIntyre RS, Filteau MJ, Martin L et al. Treatment-resistant depression: definitions, review of the evidence, and algorithmic approach. J Affect Disord 2014;156:1-7.

7. Kennedy SH, Lam RW, Parikh SV, Patten SB, Ravindran AV. Canadian Network for Mood and Anxiety Treatments (CANMAT) clinical guidelines for the management of major depressive disorder in adults. Introduction. J Affect Disord 2009;117 Suppl 1:S1-S2.

8. McIntyre RS, O’Donovan C. The human cost of not achieving full remission in depression. Can J Psychiatry2004;49(3 Suppl 1):10S-16S.

9. McClintock SM, Husain MM, Wisniewski SR et al. Residual symptoms in depressed outpatients who respond by 50% but do not remit to antidepressant medication. J Clin Psychopharmacol 2011;31(2):180-186.

10. Asmundson GJ, Katz J. Understanding the co-occurrence of anxiety disorders and chronic pain: state-of-the-art.Depress Anxiety 2009;26(10):888-901.

11. Lynch ME. What Is the Latest in Pain Mechanisms and Management? Can J Psychiatry 2015;60(4):157-159.