Comprehensive Approach to Evaluating Patients With Chronic Pain

Introduction

In the United States, chronic pain is one of the most common reasons adults seek medical care. It has been linked to anxiety, depression, poor mobility, dependence on opioids, and poor perceived health and quality of life. Based on epidemiologic data from the 2016 National Health Interview Survey, the Center for Disease Control and Prevention (CDC) estimated that approximately 20% of adults had chronic pain, and 8% had high impact chronic pain (chronic pain that inhibited daily functioning).

Chronic pain patients are disparate, with varying underlying pathophysiology and widely diverse impacts on quality of life, function, and demands on the healthcare provider and society. All chronic pain reflects an amalgam of biologic, psychological, and social factors that is best assessed with a multidimensional perspective to determine further evaluation and treatment options. This evaluation requires a systematic examination of biomedical contributors to pain and the influences of psychosocialfactors, sleep disturbances, physical capability, and medical comorbidities. The physical and psychological evaluation of chronic pain appropriately assesses a range of pathophysiologic and psychosocial processes that may underlie a patient’s presentation. This evaluation can be straightforward in a patient with less complicated circumstances but may require a multi-disciplinary team in more complex situations. The basis for the evaluation is a comprehensive assessment that includes a complete and thorough history, physical examination with particular attention to the musculoskeletal and neurologic examination, and related functional limitations, as well as an assessment of psychosocial and contextual factors, including work and social roles.

In this volume, many specific chronic pain disorders are discussed, including particularly relevant physical examination and diagnostic procedures that are appropriate. In this chapter, we attempt to provide a conceptual approach that may serve to guide the assessment of all chronic pain patients regardless of any underlying pathology or disease. Depending on the specific presenting symptoms, imaging and laboratory testing and the focus of the physical examination will vary. We will focus on low back pain (LBP) as one of the most common chronic pain problems, but the principles apply to most chronic pain conditions.

Pain Definition

The International Association for the Study of Pain has recently updated the original 1979 definition to reflect advances in the understanding of pain and to acknowledge that pain may exist even in the absence of objective physical pathology. The revised definition states that pain is “an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage,” and is expanded upon by the addition of six key notes and the etymology of the word pain for further valuable context:

• Pain is always a personal experience influenced to varying degrees by biologic, psychological, and social factors.

• Pain and nociception are different phenomena. Pain cannot be inferred solely from activity in sensory neurons.

• Through their life experiences, individuals learn the concept of pain.

• A person’s report of an experience as pain should be respected.

• Although pain usually serves an adaptive role, it may have adverse effects on function and social and psychological well-being.

• Verbal description is only one of several behaviors to express pain; inability to communicate does not negate the possibility that a human or a nonhuman animal experiences pain.

Pathophysiology of Chronic Pain

When pain persists beyond the typical time frame for acute pain to resolve, it has transitioned from acute pain to chronic pain, commonly reflecting different underlying mechanisms for the pain resulting in a sustained process. It may no longer be closely linked to actual or threatened tissue damage, even though an insult to the body may have initiated the pain. Processes contributing to the perception of ongoing pain variably include structural and biomedical causes, psychological factors both pre-existing and those arising coincident with the pain, family and social issues, prior pain experiences and trauma, and cognition. The development of chronic pain often involves both central and peripheral sensitization. However, it is often difficult to determine which of these mechanisms is predominant in a clinical context.

A detailed discussion of pain pathophysiology is beyond the scope of this chapter, and further details can be found elsewhere in this text (see Chapters 8 and 9). We will touch on a clinically based way of thinking of pain classification and the implications for treatment. Pain is commonly classified as nociceptive, neuropathic, peripheral, or centralized, which reflect presumed mechanisms and influence treatment choices and responses, therefore making the distinction between these three broad concepts clinically meaningful.

Nociceptive pain is closely tied to activation by stimuli in the body that cause damage or threaten tissue damage. At least a component of nociceptive pain is associated with a bodily affront (e.g. trauma, surgery, disease progression) and is also associated with a range of chronic musculoskeletal conditions with mechanical, compressive, inflammatory, ischemic, or infectious insults. Medical disorders associated with ongoing nociceptive signaling include degenerative, inflammatory, and neoplastic diseases. Nociceptive pain is typically localized, provoked by use or stimulation of the painful area, and may respond to physical interventions (i.e. rest, heat, ice, bracing, surgical treatment) or traditional analgesics such as anti-inflammatories or opioids. Nociceptive pain often has characteristics familiar to most individuals—aching or sharp with intensity related to stimulation of the area.

Neuropathic pain is caused by a disease or lesion of the somatosensory nervous system that results in pain, often accompanied by increased sensitivity, sensory loss or alteration, and spontaneous or evoked pain. The terms peripheral sensitization (PS) and central sensitization (CS), described in additional detail below, refer to states of abnormally increased responsiveness of the nociceptive system, which can be experienced in multiple painful conditions, including neuropathic pain. Neuropathic pain can be caused by trauma, compression, metabolic disease, toxins or medications, or autoimmune disorders. Neuropathic pain accompanies many conditions. ^, The initial insult can be in the peripheral or central nervous system with various conditions: diabetic neuropathy, surgery or trauma, stroke, or spinal cord injury. Chronic radiculopathy is an example of chronic neuropathic pain where there may be no detectable ongoing pathophysiology. Motor or sensory nerve damage typically leads to loss of function in either motor or sensory function, but in the case of neuropathic pain along with loss of function, there is an alteration in the peripheral and/or nervous system resulting in enhanced pain transmission. Patients often describe burning, tingling, or sensitivity with pain provoked by normal stimuli (allodynia) or increased painful response to a stimulus that normally provokes pain (hyperalgesia). Neuropathic pain rarely responds well to traditional analgesic medications.

Although nociceptive and neuropathic pain are familiar to most clinicians, the concepts of CS and PS may be less so. Changes in the central nervous system (CNS) and or peripheral nervous system (PNS) processing of pain are prominent components of many chronic pain conditions and are observed in the transition of acute pain to chronic pain. Altered pain processing in the spinal cord and brain coupled with a decreased ability of the CNS to diminish response to peripheral stimuli known as impaired pain modulation are the key components of CS. These changes amplify the response to peripheral stimuli, at times leading to allodynia (a typically nonpainful stimulus is perceived as painful) and/or hyperalgesia (a normally painful stimulus that has heightened intensity) in a fashion similar to neuropathic pain but without evidence of specific insult or disease of the somatosensory nervous system.

In the case of PS, an afferent nerve in the periphery that has undergone an insult has increased responsiveness with a reduced threshold to stimulation of receptive fields. These changes may be near the injury site or at the dorsal root ganglia and likely involve multiple mechanisms. This leads to increased pain perception and can be a major factor in hyperalgesia or allodynia.

Altered pain processing was initially recognized in less well understood pain conditions, with fibromyalgia (widespread chronic pain and other associated symptoms) as the prototypical example. However, CS has been identified in many other conditions, including chronic back pain, cervical pain and whiplash, osteoarthritis, pelvic pain, and sickle cell disease.

Clinicians should consider CS when there are multiple sites of pain, pain provoked with a low level of stimulus without obvious structural problem or associated nervous system injury, or pain that does not respond to traditional treatments (analgesics, modulating procedures—such as steroids or nonsteroidal anti-inflammatory drugs). An increasing number of chronic pain conditions have had CS identified in a subset of those with the condition. Therefore it is likely that many chronic pain patients have at least a component of CS. Findings to distinguish patients with CS from other chronic pain patients can be found using experimental diagnostic tools not typically used in clinical practice—functional magnetic resonance imagine (MRI), quantitative sensory testing, and conditioned pain modulation.

As there are no clinically relevant, commonly used diagnostic tests to determine CS, the diagnosis depends on clinical suspicion, history, and physical examination. Identifying CS is important as it allows for an appropriate treatment focus and can help avoid iatrogenic problems. For example, patients with CS and/or PS may have worsened outcomes after surgery, including more pain, higher complication rates, increased opioid consumption accompanied by increased costs.

Assessing Chronic Pain

There is an understanding that given the range of overlapping etiologic, mediating, and moderating factors associated with a diagnosis of chronic pain and subsequent disability, the assessment appropriately takes a broad look from many perspectives. The key elements of the assessment include:

• history of the pain reports and treatments, along with a review of systems and medical, surgical, and social history to put the current pain in context;

• impacts of the pain of function, mood, sleep, social roles, and interactions with others;

• understanding the patient’s perspective on the cause of pain, its impact, and expectations;

• physical examination including musculoskeletal and neurologic examinations plus careful observation of pain related behaviors; and

• diagnostic testing.

These assessments are affected by many factors that variably and uniquely interact and include:

• genetics,

• structural or physical changes and pathology,

• CNS and PNS processing such as sensitization and inhibition,

• prior experiences with pain and the medical system,

• psychological factors ranging from psychopathology to coping style,

• belief systems, and

• environmental influences (work, disability, family, societal, financial).

A comprehensive evaluation examines each factor listed above and weighs its importance in the patient experience. The role of genetics in pain assessment and treatment has not yet been clearly defined. Therefore we will focus on a strategy for assessing the other factors that contribute to chronic pain in this chapter.

What Is the History of the Pain?

The first component of assessing patients reporting pain is centered on classic history taking:

• Onset—when did the pain start?

• Location—where does it hurt (all locations)?

• Duration—how long have they had pain; how long does it last when they experience pain?

• Character/description—what does the pain feel like?

• Intensity—how severe is the pain?

• Alleviating factors—what makes the pain better?

• Aggravating factors—what makes the pain worse?

• Radiation—does the pain spread?

• Temporal pattern—does the pain vary throughout the day, has it evolved over time?

• Associated symptoms—how does the pain impact the patient (function, mood, sleep, work, relationships)?

It is important to explore when the patient believes the pain began, whether its onset was insidious vs. attributable to a particular event, trauma, or underlying medical condition, and what the patient believes is the cause(s) of their ongoing pain. Patients’ interpretation of their pain provocation and relief is very important to understand the illness narrative whether or not the provider feels it is “logical” or not. Investigating a patients’ interpretation of cause, severity, variability over time, exacerbating and relieving factors, and any effects of prior treatment help frame the current situation and future treatment options.

A patient’s illness narrative may not align with a providers’ biologic model of pain but is critical to understanding the entirety of the patient’s experience, which is needed to understand and treat the patient effectively. It is worth noting that in evaluating a patient with chronic pain, the healthcare provider should pay careful attention to certain historical items that are considered only cursorily in other clinical settings. In particular, the healthcare provider should be careful to assess the patient’s history for early childhood physical and emotional trauma, early onset of painful conditions, chemical dependency, sleep disturbance and potential for obstructive sleep apnea, apparent severity of incapacitation, and his or her status with respect to litigation and compensation.

Using a body map/pain drawing where patients indicate the location(s) of their pain may be useful. Patients are asked to shade in on the drawing everywhere they experience pain, not just the present reason for evaluation. The assessment can be on paper or in a computerized form. The latter allows for the analysis of the data to make it more quantifiable. This visual display of pain allows for quick recognition of patterns: diffusely filled in diagrams consistent with fibromyalgia, shaded areas that extend from the neck or back to the hand or foot typical of radicular pain, localized and unilateral drawing consistent with sacroiliac joint pain. More widespread pain filled in on a body diagram is associated with both increased disability and poor outcomes after a surgical intervention such as total knee arthroplasty. ^,

Assessment of Physical and Medical Factors

A thorough physical evaluation is a basic element in the evaluation of a patient with chronic pain, and while it serves many functions, examination findings are always placed in context with a thorough history. The examination serves many purposes, including:

• assessing function (e.g. gait, strength, range of motion, balance, speed, fluidity) and the patient’s awareness of their functional status,

• making diagnoses and collaborating findings with history, imaging, and other diagnostic testing,

• determining if the pain problem is localized (one body region or system) or more generalized,

• determining treatment options and goals (palliation, correction of pathology, functional restoration), and

• determining if referral to a specialist is warranted.

Patients may focus on only their most recent or current pain, or a provider may only investigate the “chief complaint” and not put the pain in the appropriate context if a patient has more diffuse pain. Given the widespread nature of many chronic pain patients’ conditions and the possibility of multiple pain sites or recurrent pain, all patients should have a thorough physical examination at their initial visit with an emphasis on musculoskeletal and neurologic examinations well as on their primary area where symptoms are reported. If pain is indeed focal, examining the normal areas confirms that the pain is localized, and the examination can be quickly and efficiently accomplished. Also, evaluating a pain patient depends on the chronicity of the patient’s symptoms and the evaluations and diagnostic testing that the patient has already undergone.

To be reasonably specific, the discussion here focuses on evaluating a patient with a chief symptom of back pain. LBP is the most common chronic pain condition with a point prevalence of 13% in the United States and is a leading reason for seeking health care and cause of disability worldwide. LBP is the most common reason for long term opioid use in the United States. Patients with chronic LBP tend to be socioeconomically disadvantaged, visit healthcare providers frequently, and have a high burden of comorbidities. The differential diagnosis of chronic LBP ranges from “non-specific” to serious, potentially life-altering illness. Many structures in the back can cause pain, including muscles, facet and sacroiliac joints, nerve roots, disc, ligaments, or adjacent structures. Thus the differential diagnosis list is long. Psychological and social factors have long been recognized as important and must be appropriately assessed and addressed. ^, We will discuss how the differential diagnoses can be further narrowed and a management plan developed through each assessment element.

Physical Examination

The details of physical examination are covered separately in Chapter 18 on specific disorders in this volume; however, we want to re-emphasize the importance of conducting a thorough physical examination of all patients. Decisions about imaging and diagnostic studies should be made when correlation and confirmation is needed between a physical finding, history, and possible pathology.

Red Flag Symptoms Associated With Back Pain

In any initial evaluation of a patient reporting persistent pain, the first concern is always to evaluate for any “red flag” symptoms indicative of a serious underlying medical condition that warrant additional evaluation and possible treatment. Examples of a serious medical condition would include malignancy, infection, significant trauma with damage to spinal elements, or neurologic injury. Symptoms, history, or findings that might represent a red flag include weight loss, profound fatigue, progressive motor or sensory deficits, constant new onset of severe pain, change in bowel or bladder control, fever, history of cancer or infection, advanced age, prolonged use of steroids, or immune compromised. The presence of multiple red flag symptoms increases the probability of serious underlying pathology. ^,

Neurologic Injury

Healthcare providers should be alert for clinical evidence of either radiculopathy, neuropathy, or myelopathy and should recall that a peripheral nerve injury can at times mimic a spinal problem. Radiculopathy is a condition that affects the function of a nerve root, often accompanied by pain and changes in sensation, strength, and reflexes in a specific dermatomal distribution. Myelopathy refers to a neurologic deficit from injury or disease of the spinal cord. On pain history, patients often report a burning or intermittent stinging pain that radiates to various locations throughout their bodies. Patients may identify an inciting event in the lumbosacral region when radiculopathy is because of a disc herniation. Patients may report pain or numbness specifically in a known dermatomal distribution, but at times the complaint is vague, such as “my whole leg is numb,” which requires investigation to determine if the complaint represents myelopathy or a more benign vague non-specific sensory change. At other times, patients may complain of numb feet, but on further investigation, it becomes apparent that they have a separate peripheral neuropathy. Similarly, patients may report weakness or loss of fatigue that may represent myelopathy, radiculopathy, another medical condition, or simply deconditioning. Clinicians need to obtain the history in a manner that helps distinguish patterns and narrow the differential diagnosis. Additionally, if a patient has a history of significant trauma associated with the onset of pain or malignancy, urgent attention should be paid to evaluating instability of the spine, compression of neural elements, or metastasis.

Since it is not uncommon for patients to have complex multifactorial pain presentations, it is important to perform a careful sensory, strength, and reflex examination to determine differential diagnosis, need for further diagnostic testing, and treatment options. If needed, electrodiagnostic studies provide more objective evidence for radiculopathy and help distinguish it from peripheral nerve injury. MRI scan may also help provide evidence of an anatomic abnormality of nerve roots or anywhere along the spinal cord. It is important to remember that there are high rates of incidental findings in asymptomatic patients, so imaging should be used to confirm clinical examination findings that are consistent with positive physical pathology. If the patient is asymptomatic for a given finding on examination but has incidental findings on imaging, they are unlikely to be meaningful.

Spinal Stenosis

Lumbar spinal stenosis is a common condition (11%-39% of the population) with variable clinical presentation, multiple treatment options, and increased prevalence with age. Lumbar spinal stenosis refers to narrowing of one of three anatomic areas, most commonly of the central canal, but also the lateral recess or neural foramen. The narrowing can be congenital, but more commonly, changes in the structure (disc protrusion, disc height loss, facet arthropathy, osteophytes, ligamentum flavum hypertrophy, spondylolisthesis, fibrosis) result in narrowing that compromises the neural elements. Typically, pain in the back or legs (neurogenic claudication) is brought on by activity such as walking or prolonged standing and relieved with rest or forward flexion. The physical examination findings for lumbar spinal stenosis are often non-specific.

Musculoskeletal Sources of Pain

The differential diagnosis of LBP is complex. Aside from neurologic injury or compression and spinal stenosis, many musculoskeletal structures in the back can be a source of pain: facet joints (paired joints at each level), sacroiliac joints (at the junction of the sacrum and pelvis), ligaments (multiple areas), muscles (back and gluteal), bone (compression fracture), and intervertebral disc (with degeneration). LBP that stays confined to the low back and does not radiate beyond the knee is also known as axial LBP. Commonly musculoskeletal pain can be because of an acute insult, degenerative processes, or chronic deconditioning and poor posture. During history gathering, patients may endorse insidious onset and difficulty with their overall range of motion. On physical examination, pain may be provoked with specific movements or palpation that may help focus the differential diagnosis. It is important to recall that multiple sources of pain can co-exist. In our clinical experience, muscle pain commonly co-occurs with all of the other sources of LBP.

Risk Factors for Poorer Outcome Or Delayed Recovery

Some patients do not respond as well to treatments as the “typical” patient, with persistent pain, dysfunction, and sufferingdespite treatment that appears to be “appropriate”. It is difficult for a clinician to predict who is at risk for minimal benefit from treatment or who will experience slower recovery; the literature does not provide a clear guide. This list of possible risk factors for ongoing, poorly controlled pain includes medical and psychosocial factors. The more of these risk factors a patient has, the more likely they are to have pain that is difficult to treat.

• Identifiable progressive medical condition with known impact on the musculoskeletal or nervous system (e.g. rheumatologic diseases, multiple sclerosis, poorly controlled diabetes)

• More severe structural burden (e.g. failed fusion, uncorrected scoliosis, poly-trauma)

• High pain intensity, particularly pain that does not vary in intensity

• Repeated surgical or other procedures intended to relieve the same pain condition

• Widespread pain, other symptoms, or signs of CS

• Long term opioid use

• Substance abuse (opioid, alcohol, stimulants, tobacco, sedatives)

• Severely compromised function

• Preexisting mental health issues including post-traumatic stress disorder, poorly controlled anxiety, and depression

• Sleep disturbances both sleep apnea and difficulty initiating or maintaining sleep

• Social factors: unstable housing, poverty, low literacy, limited access to medical care, lack of support, physically demanding work conditions

• Medical illness that compromises function or limits treatment option ^,