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Chronic Pain: Evolution of Clinical Definitions and Implications for Practice


Numerous definitions of pain have been proposed over many years with different implications when applied to clinical practice. This paper reviews information regarding the evolution of definitions of pain terminology and pain syndromes as they relate to everyday practice for clinicians and those operating within the medicolegal judicial system, both trainees and seasoned professionals, with a focus on chronic pain. An historical overview of the evolution and chronology of chronic pain labels and definitions is provided with emphasis on those used currently in clinical practice. Subsequently, the paper mainly concentrates on the two more recent revisions of the Diagnostic and Statistical Manual of Mental Disorders (DSM) of the American Psychiatric Association (APA) and the basic principles of International Classification of Diseases (ICD) by the World Health Organization (WHO). It further provides a summary of the newly accepted WHO ICD-11 novel classification of pain disorders, a joint effort of WHO and the International Association for the Study of Pain (IASP). We conclude our review by providing our personal opinions and commentaries on controversies and dilemmas associated with the DSM, and ICD pain definitions and classifications, and offer useful tips for those who perform forensic examinations.

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We thank Dr. F. Lakha for her help with the references of the manuscript.

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Appendix 1 CPP illustrative case reports

CASE REPORT #1: Mr. DP is a 56-year-old male who suffered a traumatic amputation of the right index and middle finger at work in 1981. This led to intense PTSD symptoms, such as nightmares, which though improved, continue to occur at night at times of stress. Bilateral lower leg pains appeared a few months after the amputation and gradually spread throughout his body. Further axial pain and significant driving anxiety developed after a car accident in 2012. After a choking episode in 2013, which generated a near-death experience, he went on to further develop panic attacks and eating-related anxiety. Medications upon presentation in March 2019 included pregabalin 150 mg hs, antacids, and the rare lorazepam for panic attacks. Past medications include a multitude of SSRIs, SNRIs, and nabilone with no therapeutic effect or multiple side effects.

Mr. DP has been married for 16 years and has 2 step children and 4 grandchildren. He lives in a house with his wife. He is independent with ADLs and IADLs. He has taken multiple mental health-related leaves of absence from various jobs. He is currently on short-term disability from his full-time job at the Canadian Mental Health Association as a Housing Project Manager. He also works part-time as a professional musician.

On presentation at the age of 56, he scored 64/70 of pain interference on the Brief Pain Inventory, 23 on the PHQ-9 (severe depression), and 21 on the GAD-7 (severe anxiety). In a body diagram, he shaded his axial spine particularly to the right and legs though at times he reported total body pain. His pains ranged in intensity from 2 to 12/10, averaging 6/10 aggravated by psychological stress, physical activity, sitting and prolonged standing, and relieved by playing guitar, hot showers, topicals and massage.

O/E Mr. DP he was pleasant and devoid of overt pain behaviors. Neck and low back ranges of motion were moderately decreased in all directions due to end-range local pain. Reflexes and motor strength were normal, with minor inconsistent patchy right leg hyper/hypoesthesia. However, on re-evaluation 2 months later, the patchy sensory alterations spread to the entire right hemibody, excluding the face. The physical examination was otherwise completely unremarkable.


DSM-IV: Chronic pain disorder associated with psychological factors (severe); panic disorder; PTSD.

DSM-5: Somatic symptom disorder with predominant pain, chronic, severe; panic disorder; PTSD.

ICD 11: chronic primary pain; MG30.01 CWP or MG30.01 MSK.

CASE REPORT #2: Mr. LP is a 37-year-old male seen for chronic widespread pain on August 2019. In the winter of 2015, he had an episode of flu-like symptoms followed by persistent fatigue and brain fog. When he started biking in the spring, he immediately began to experience muscle spasms and tightness in his legs and arms. Since then, with every activity he does, and within minutes, he begins to experience pain, spasms, and tightness in whatever muscle group is engaged. A rheumatologist ruled out inflammatory arthropathy and tetanus and considered the diagnosis of fibromyalgia.

When seen in our pain centre four years after the onset of his pains, he scored 37/70 on the Brief Pain Inventory (BPI) regarding pain interference, 8 on the PHQ-9, and 5 on GAD-7, indicating mild depression and anxiety, respectively. He was frustrated with his pains and disability and had sought repeatedly other medical opinions. He shaded his back, legs, and arms in a body diagram as sites of pain. He described his pain as intermittent “tightness, pain, and muscle spasm” in his back and limbs, intermittent paraesthesia into his hands and legs, and aggravation of pain within minutes of using his muscles and relieved with rest. He reported as well associated fasciculations (rippling of muscles, which he said he has seen or felt under his fingers occasionally in leg or arm muscles), brain fog, and fatigue, which all were partially relieved with the use of naproxen. He rated his pain as 4/10, ranging from 3 to 7/10. He complained additionally of sleep fragmentation, fatigue, snoring, significant weight gain, despite limited appetite and irritable bowel symptoms.

Past history included psoriasis and asthma. Mr. LP was married, had no children and was self-employed in a start-up game company. He had abandoned cycling and all outdoor activities. He had to take multiple breaks throughout the day, his ability for household chores had diminished over time, and his socialization had much decreased. His only medication was naproxen b.i.d.

O/E Mr. LP was a pleasant, quite obese young man with no pain behaviors. There were bilateral psoriatic patches in his legs. General MSK and neuroexamination were unremarkable, but he complained that repetitive squats and push-ups recreated the “spasms and tightness.” Palpation revealed tenderness over the trapezius muscles bilaterally. No visible fasciculations were observed.

Diagnosis at this point in time:

DSM IV: Chronic pain disorder associated with psychological factors (mild) and? a general medical condition (diffuse cramps not yet diagnosed?).

DSM-5: Somatic symptom disorder with predominant pain (chronic, mild).

ICD-11: Chronic primary pain; MG30.01 CWP or MG30.01 MSK.

The pain team did not feel the patient had fibromyalgia or that he had been properly investigated, and we repeated blood work and followed the patient regularly. Extensive blood work was repeatedly normal, including ESR, except an CRP (general index of inflammation). We decided to discontinue his NSAIDS for a week while monitoring his CRP. Discontinuation of his NSAIDs seriously aggravated his “tightness” and led to a remarkable rise in his CRP values. The provisional diagnosis of (seronegative) psoriatic spondyloarthropathy with peripheral manifestations (enthesopathy) was made by the pain team. Referral to another rheumatologist associated with our program confirmed the diagnosis. Currently, the patient is on DMARDs (disease modifiers) with excellent response.

Revised diagnosis:

DSM-IV: None.

DSM-5: None.

ICD-11: Chronic secondary MSK pain MG30.3

Comment: This patient’s undiagnosed medical condition rendered him the label of chronic primary pain/ fibromyalgia (which practically means pain not yet diagnosed or NYD) until a medical diagnosis was established, at which time his diagnosis was moved to ICD-11 secondary MSK pain.

CASE REPORT #3. Ms. EF, a 21-year-old female, presented to our center in January of 2017. She had been hit on her left side by a car in 2015 and developed excruciating pain in the medial aspect of her left calf and foot, for which she received extensive physiotherapy and multiple injections (the latter worsened her pain). She scored 67/70 of pain interference on the BPI (high level) and marked her left shoulder, lower back, glutei, and the left shin and foot as her areas of pain on a body map (the foot, however, was her dominant pain described as constant and sharp with extreme sensitivity to touch, coldness, intermittent swelling, and significant discoloration on dependency). She rated her foot pain as 9–10/10 during the consultation, ranging from 6 to 10/10. Her sleep was severely disrupted due to pain, she had gained > 45 lbs of weight since the injury, she still had nightmares relating to the accident, and she was anxious as a passenger though she had somewhat improved.

Medications included amitriptyline (100 mg) OD and duloxetine (30 mg) OD. She lived with her boyfriend in her mother’s basement. She used to work as a hairstylist but had to stop due to the inability to weight bear on the left leg. She had an open legal case relating to the accident.

O/E Ms. EF was an overweight female ambulating with a single point cane in the right hand favoring the left leg. She had contractures of the left heel cord due to her 1.5 years walking on the left tiptoes. The left leg appeared discolored on dependency with puffiness in the foot dorsum, her calf wasted and was significantly allodynic and hyperalgesic with sensitivity much worse over the medial arch and sole of the left foot. Temperature measured with a sensitive laser probe revealed that the left knee was warmer by 2 °C and the left foot colder by 1.6 °C compared to the right side.

She was diagnosed with “cold” CRPS and met both sets of symptoms and sign categories of the Budapest Clinical Diagnostic Criteria. Pregabalin was initiated and titrated upwards while she was offered a number of interventional procedures. Interdisciplinary management including psychology, manual therapy, mindfulness meditation, and nutrition for better weight management, was offered as well as part of supportive therapy. She opted for a trial of IV ketamine infusions (to no avail), and finally, on October 16, 2017, she had a spinal stimulator implanted via a percutaneous approach after a successive trial. She was reviewed 2 weeks later. Her pain had been reduced from 9 out of 10 to 3–4 out of 10, her allodynia/hyperalgesia was literally gone except a small area in the medial foot, and despite some fluctuating temperature in the left foot, on dependency the temperature equalized quickly with that of the right foot. The patient was followed monthly while she continued with intense physiotherapy. Within 6 months she had remarkable improvement, including loss of 55 lbs of weight, near-complete stretching of the heel cord contractures, reversal of the calf wasting, normalization of gait, and nearly complete pain elimination (though pain would return 20 min after turning the stimulator off). In the fall of 2019, she registered at the University to take a 2-year clinical teacher course and has successfully completed year #1.

Diagnosis (at the time of presentation (January 2017)):

DSM-IV: Chronic pain disorder associated with psychological factors (moderate to severe) and a general medical condition (CRPS); PTSD symptoms (though she did not meet criteria for the full disorder).

DSM-5: Somatic symptom disorder with predominant pain (moderate to severe); PTSD symptoms (did not meet criteria for full disorder).

ICD-11: Chronic primary pain MG30.0 (plus 8D8A.0 CRPS from the ICD-11 chapter on Disorders of the Autonomic Nervous System and cross-linked to CPP).

Revised current diagnosis:

DSM-IV: None.

DSM-5: None.

ICD-11: 8D8A.0 CRPS from the ICD-11 chapter on Disorders of the Autonomic Nervous System.

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Mailis, A., Tepperman, P.S. & Hapidou, E.G. Chronic Pain: Evolution of Clinical Definitions and Implications for Practice. Psychol. Inj. and Law 13, 412–426 (2020).

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  • Chronic pain
  • Musculoskeletal
  • Neuropathic
  • Nociceptive
  • Nociplastic