Managing treatment-resistant depression in the setting of chronic pain

Among the many challenges of treating depression are the complications that arise when the depression is concurrent with other medical conditions. Not surprisingly, when a patient has two conditions, insufficient treatment of one condition may worsen the presentation or treatment outcome of the second condition. This is particularly true when dealing with concurrent mood problems and pain problems. Such complications arise from the bidirectional relationship between depression and pain ( ). Individuals with serious acute pain that progresses to chronic pain are at higher risk for developing various psychiatric disorders, particularly depression. Patients with depression experience various physical symptoms, and various attributes of depression, including reduced energy and reduced ability to exercise, may, in turn, predispose to exacerbation of pain conditions. Chronic pain often generates pessimistic thoughts and feelings of frustration and helplessness; in turn, this cognitive frame allows for the evolution of depression as a clinical problem. At an even more fundamental level, the neural pathways for pain and the neural pathways for mood disorders share some common brain regions and certainly share many common neurotransmitters, particularly serotonin as a major signaling molecule ( ; ). As the body tries to compensate for one condition by altering some attribute of the neurotransmitter in the initially affected system, this may in turn cause disruption of pathways that use the same neurotransmitter in the other system. Furthermore, once the individual has progressed to have depression and chronic pain, treatment for each condition independently may either help or hurt the other condition. Finally, when two disorders are present, it is common for both the patient and the clinician to focus treatment efforts on one disorder with the hope that any other sequelae will fade with the treatment of what is perceived to be the primary disorder. Treat the pain, and the depression might disappear, or treat the depression and the pain may lessen—so goes the mantra. Unfortunately, the reality is that by focusing on only one of two concurrent disorders, both conditions ultimately get treated more poorly.

In this chapter on the intersection between refractory depression and chronic pain disorders, we will begin by defining what constitutes chronic pain disorders since the definition of chronic or refractory depression is to be found elsewhere in this volume. We will look at the prevalence of pain disorders and in particular look at a couple of practical strategies to monitor the pain in the same spirit of measurement-based care that we typically apply to the management of mood disorders. Once we have established these common definitions in matrix, we systematically explore several key questions around the interface of depression and pain. From an epidemiologic perspective, we clarify how common pain is in depressed patients and conversely how common depression is in pain patients. Next, we moved to treatment by evaluating whether the presence of depression affects clinical outcomes in chronic pain treatment and the parallel question of whether pain affects depression outcomes. Finally, we look at the various treatments that have been explored for the interface of treating depression in the context of a chronic pain disorder.

Definition and measurement of chronic pain disorders

The International Association for the Study of Pain (IASP) defines chronic pain as pain that lasts beyond the expected time required for normal tissue healing and/or is intractable to treatment. From purely the pain perspective, it is estimated that just over 20% of the US adult population had a chronic pain disorder in 2016, representing approximately 50,000,000 adults. The impact of chronic pain is enormous in terms of suffering for the individual and families but also for society in terms of direct and indirect economic costs, which have been estimated to be over half a trillion dollars in 2010. Proper assessment and management of chronic pain is itself a major medical subspecialty and is certainly beyond the scope of this chapter. However, it is reasonable that the clinician treating depression and particularly refractory depression will need to be able to ask basic questions about the presence or absence of pain disorders and be able to measure whether the pain disorder is getting better or worse while depression is being treated.

For any patient, assessment of the various types of symptoms of pain along with their impact on social and occupational functioning is essential. Measuring that is exactly the same as measuring the social and occupational impact of a mood disorder, so a clinician skilled in treating depression can simply apply the same approach in measuring impairment related to pain. But getting a precise metric for the pain is also necessary. Much like depression, where many clinician and patient-rated scales exist, the pain literature is also full of many patient and clinician measures of pain. We have recently published a practical guide to measurement based care for depression, highlighting how to use commonly available rating scales and how frequently to implement them in daily practice ( ). In a parallel way, two pain questionnaires, namely the McGill Pain Questionnaire (MPQ) and the Brief Pain Inventory (BPI), have been validated and are widely used and quite practical even for the clinician who does not specializes in pain. Both of these scales were originally validated for one type of pain and in the English language; subsequently, both scales have been validated in multiple languages and across diverse types of pain. Both scales are self-administered and take less than 5 min to complete. We review both questionnaires below and suggest that the clinician pick one scale and use this periodically—perhaps monthly in tandem with a mood rating scale—in the assessment of a patient who has a mood disorder and a pain disorder.

The McGill Pain Questionnaire and the Brief Pain Inventory

The McGill Pain Questionnaire ( ) and its more practical short form, the SF-MPQ ( ), evaluate sensory, affective-emotional, evaluative, and temporal aspects of the pain experience of the patient. The SF-MPQ consists of 15 questions which are divided into 11 sensory questions which identified the nature of the pain such as “sharp or shooting, etc.” and for affective verbal descriptions such as “sickening, fearful, etc.” The patient is asked to rate the intensity of each descriptor on a scale from 0 (none) to 3 (severe). Three pain scores are calculated: the sensory, the affective, and the total pain index; these are totaled to get an overall score, much like the PHQ-9. Typically, less than 5 min is needed for the patient to fill out the scale and to calculate a score. It is free to use, and widely available on the internet in multiple languages ( ).

The Brief Pain Inventory is a numeric rating scale from 0 to 10 that assesses the severity of pain and the degree of interference with functioning ( ). It measures both pain intensity and pain interference with different life domains. It includes six questions that ask for the intensity and temporal nature of the pain, including a diagram of the body on which the patient marks where the pain is felt. One question includes seven specific items to rate the impact of the pain, during the past 24 h, on functioning, mood, and enjoyment of life, again scored 0–10. Two other questions summarize pain treatment and asked the patient to rate relief of pain from the treatment. Since these questions cover a range of topics, there is no simple algorithm to generate an overall score; instead, specific answers to each question need to be compared from visit to visit. The scale is under copyright but is free for clinical practice.

Summary of recommendations for assessment practices in comorbid pain and depression scenarios

Measurement-based care is enormously helpful for the successful treatment of most medical conditions, including either depression or pain disorders. Given the additional complexity when there are two disorders, it is even more important to ensure that each condition is properly measured and monitored over time. We, therefore, make the following suggestions:

1.
As part of an assessment for a mood disorder, at a minimum ask the patient to complete the patient self-report form for depression, the Patient Health Questionnaire (PHQ-9), and the patient self-report for General Anxiety Disorder (GAD-7). Ideally, this would be complemented by a clinician-assessed scale; we recommend the Montgomery-Asberg Depression Rating Scale.
2.
As part of an assessment for a mood disorder, ask if there is a significant problem with pain, and document its location and intensity. If the patient indicates that the pain is significantly impairing, ask the patient to complete either the SF-MPQ or the BPI.
3.
In ongoing care, use a mood rating scale at regular intervals, such as once per month during active treatment without remission. During the same appointment, a single question should be asked about any chronic pain problems; if present, again administer the same pain questionnaire previously administered.
4.
In addition to reviewing depression treatment, ask about patient preferences and current practices of pain management. If the patient needs treatment of pain, explore with the patient and consider whether a referral to an outside resource for pain management is necessary.

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