The medico-legal pertinence of musculoskeletal nociplastic pain

Abstract

Pain conditions can be challenging; nociplastic pain, defined as pain that cannot be sufficiently explained by structural/anatomical changes, is newly categorised as the third pain mechanism. Nociplastic pain complaints are subjective, often accompanied by symptoms of fatigue, sleep and mood disturbance and cognitive difficulties with no diagnostic biomarker or reliable measurement of severity. Medico-legal challenges include attribution of causation after an alleged triggering event, assessment of severity, and reported functional impairment. This review considers nociplastic pain in regard to the musculoskeletal system with focus on causation and temporality of the pain condition and impairment. We hope that this overview will provide a better understanding of these challenging pain conditions.

Why should the medico-legal world understand the concept of nociplastic pain?

Chronic pain that occurs without objective tissue abnormality or clinical biomarker is challenging in both the clinical and medico-legal setting. ¹ This “unseen pain” is now identified as nociplastic pain and is accepted as the third mechanism of pain. ² Although nociplastic mechanisms have been extensively studied in a research setting with objective changes in the immune system and dysregulation of nervous system function, there is currently no consistent objective biomarker to confirm this diagnosis in a clinical setting. Clinical evaluation depends entirely on the subjective symptoms reported by an individual. This review aims to clarify many issues surrounding nociplastic pain that are relevant to medico-legal evaluation, causation, severity and functional status or impairment.

An overview of nociplastic pain

The enigma of nociplastic pain is that there is nothing to see, nothing to measure, mostly no physical finding on examination, poor response to most treatments, yet a cause of considerable unseen suffering affecting physical, emotional, occupational and social functioning. ³ Two specific nociplastic pain conditions that involve the musculoskeletal system are fibromyalgia (chronic widespread pain) and chronic primary musculoskeletal pain (chronic regional pain identified as “nonspecific” musculoskeletal pain). ⁴

Nociplastic pain occurs in the absence of tissue damage. A simplistic understanding is that the nervous system is fired up and set into perpetual motion with amplification of pain processing and diminished inhibition at multiple levels. ⁵ Although central sensitisation is commonly associated with nociplastic pain, the terminology is not synonymous. ⁶ Pain is often associated with physical and/or mental fatigue, sleep disturbance, cognitive impairment, hypersensitivity to external stimuli, and mood disturbances that occur with variable frequency in individual patients. ⁷ The psychosocial context in the expression and perpetuation of nociplastic pain is important. The composite of many biological and psychosocial variables, such as cultural, socioeconomic, underlying physical and mental health and lifetime adverse events all contribute to the final expression of illness. ⁸ In total, it is the multiplicity of these factors that contribute to the global suffering. The physical examination may be completely within normal limits for a person’s age, although some may demonstrate tissue allodynia. There is no clinical biomarker, including laboratory or imaging studies, that can confirm a diagnosis or assess severity of nociplastic pain.

Current treatments are generally not entirely satisfactory, with no “gold standard” recommendations. Management strategies aim to attenuate symptoms and improve quality of life rather than a cure. The cornerstone of care is a non-pharmacological approach that includes patient education, promotion of good lifetime habits and various psychological interventions. ⁹ Traditional analgesic treatments such as simple analgesics, muscle relaxants, nonsteroid anti-inflammatory drugs, and opioids are less effective for nociplastic pain, although commonly used. ¹⁰ Opioids are strongly discouraged. Specific anti-depressant and anti-epileptic drugs identified, as adjuvant drugs, have regulatory approval in many jurisdictions, but with generally only modest effect. Most patients with nociplastic pain experience symptoms over their lifetime and the condition generally persists.

Why does nociplastic pain occur? Genetic predisposition may occur in about one third of patients based on family studies, but with no specific genetic profile identifiable. ¹¹ Although pain may occur spontaneously for the majority, about one third of patients report its onset following a specific trigger, e.g. an illness, with recent reports following SARS-CoV-2 (Covid-19) infection, or a traumatic physical or psychological event. ¹² An event that potentially leads to nociplastic pain is often central to a medico-legal adjudication. Further, there is no “gold standard” for a timeline from an initiating event to evolution of nociplastic pain. A localised pain may spread and increase over a period of months to years, with studies extending from 12 months to five years aiming to explain this “bottom-up” concept.

Nociplastic pain and the medico-legal arena

Questions that commonly arise in the adjudication dealing with chronic pain include uncertainty about the specific diagnosis, severity of condition, causation and degree of impairment. The gap that exists between the research world and clinical practice is even wider when applied to the medico-legal field. The American Medical Association (AMA) has acknowledged that there is no objective measure to quantify pain and accepts that pain can have variable effects on the individual. ¹³ The subjective pain experience is further affected by factors described above that influence severity and its impact on function. Causation is often a contentious and central issue, and disability related to pain remains controversial with no consensus either in the literature or among experts.

The medico-legal evaluation of a person with nociplastic pain

There are three steps needed to evaluate a claimant with nociplastic pain.

The first is to read all the medical records and make an accurate synopsis of their content which should include notes written by all treating health care professionals. Particular attention should be given to the patient's health status prior to the onset of the condition under consideration. This should provide a broad understanding of the health status of a claimant and enable the evaluator to formulate a preliminary opinion of the situation.

Step two: The claimant should be interviewed to provide a complete and detailed narrative history of the clinical condition. This is assisted by the evaluator asking pertinent questions that guide the claimant to provide relevant information. Their past medical and mental health history, including any substance use or abuse, as well as family history should be noted along with previous pain experience(s) and any physical or psychological adverse events. How and when did the pain begin? Details of its onset and evolution, any precipitating event, quality of pain, fluctuation in location or intensity, and alleviating or aggravating factors should be sought out. Symptoms such as sleep disturbance, fatigue, poor cognition, hypervigilance and mood disorders should be explored, as well as their impact on normal daily activities, with comparison to activities undertaken prior to illness. All treatments should be noted, with particular attention to excessive prescribing of medications that could contribute to symptoms.

The third component of the evaluation is a physical examination. This may be entirely within normal limits. Muscle strength and joint range of motion should be normal or consistent with the patient age. Allodynia may be present. Dynamic mechanical allodynia is examined by gently stroking the skin with a cotton pad or soft brush; static mechanical allodynia by digital palpation with a weight equivalent of 4 kg, cold or heat allodynia with a metal object (20°C) or cup of water (40°C). Persistence of sensation after the stimulus has ended is indicative of “after sensation”. ¹⁴ Notable is that pain sensitivity does not follow traditional dermatomal distributions.

Function in persons with nociplastic pain

Function in persons with nociplastic pain can vary from day to day due to symptom fluctuation. The assessment is entirely dependent upon subjective report of the individual’s perception of their abilities, as well as report of increased symptoms related to physical activity or after maintaining a prolonged static position. There are also currently no standards or recommendations for functional restrictions for those with nociplastic pain. ¹⁵ As fatigue (physical and mental) is an important component of nociplastic pain, a shortened work week can offer an advantage for recovery of energy, but is not an established criterion in the medical literature. ¹⁶ It is generally recommended that patients should remain in the workplace with reasonable adjustments. Prolonged absence is detrimental to mental, physical and social well-being. Performance-based functional assessments have mostly focused on the physical factors rather than a more comprehensive and integrative social, mental and biological perspective. ¹⁷

Specific medico-legal challenges

Over the past three decades chronic pain has presented many challenges in medico-legal adjudication. Contrary to most health conditions where healthcare professionals are confident in diagnosis and management, chronic pain, particularly nociplastic pain, is elusive in its absence of traditional objective physical or biomarker abnormalities. Determining whether an event caused the condition, or aggravated a pre-existing condition, is likely to be the most contentious issue. Another consideration is the risk of over-diagnosis of a condition whose existence cannot be objectified or satisfactorily proved. Unfortunately many clinicians and more specifically medico-legal evaluators lack sufficient knowledge and understanding of chronic pain conditions. Ideally, a person with chronic pain in a medico-legal setting should be evaluated by a clinician with expertise in all aspects of diagnosis and management of painful conditions and with competence to provide a comprehensive multi-dimensional assessment.

Conclusions

Nociplastic pain offers validation for challenging pain conditions that cannot be objectively proved. Although grounded in solid science, the clinical evaluation of nociplastic pain relies on subjective reporting and with so many uncertainties nociplastic pain remains a challenge in the medico-legal setting. Furthermore, although clinicians working in pain medicine more easily accept the evolving nature of pain conditions, this is less common in other medical disciplines and to lawyers. Until standard texts such as the AMA guides are updated to acknowledge and include nociplastic pain, challenges in the adjudication of an individual claiming it will persist and will be influenced by the competence of the experts providing evidence.