Neurobiological Mechanisms of Whiplash

Neurobiological Mechanisms of Whiplash

Samuel A. McLean

Among individuals involved in one of the fifty million motor vehicle collisions (MVCs) that occur worldwide each year [37], persistent musculoskeletal pain is a common and costly public health problem [7]. The purpose of this chapter is to provide a contemporary understanding of neurobiological mechanisms mediating persistent symptom development after MVC. The past two decades have witnessed the increasing application of molecular techniques to gain insight into the pathogenesis of post-MVC pain. However, the most important advance in understanding neurobiological mechanisms mediating post-MVC pain outcomes has been the evolution to a more accurate and complete characterization of the phenotype. This is of critical importance because if the phenotype is not accurately characterized, then it is unlikely that any amount of application of bioinformatic, statistical, or “omics” techniques will yield valid information. Candidate neurobiological systems responsible for the pathogenesis of post-MVC neuropsychiatric sequelae will then be reviewed, with an emphasis on those domains most fruitful for future study.


From Pain in the Neck Region to Pain Potentially Occurring in Many Body Regions as Part of a Frequently Multidimensional Posttraumatic Neuropsychiatric Disorder

More recently, large-scale studies have shown that pain after MVC may occur in many different body regions (e.g., low back [9]), and/or may be widespread [25, 26, 50, 51]. For example, in one recent study of 948 individuals enrolled in the emergency department (ED) in the immediate aftermath of MVC, pain outside of the neck region at the time of ED evaluation was the norm, and 22% had pain in 7 or more body regions
[33]. At 6 weeks, moderate or severe low back pain was as common as neck pain (with a prevalence of 37% for each) and overlapped with neck pain in only 23% of patients [4]. Further, pain across all body regions accounted for nearly twice as much of the variance in pain interference as neck pain alone (60% vs. 34%). Similarly, in two large cohorts of individuals experiencing MVC who presented to the ED after MVC and were discharged to home after evaluation, 6 weeks after MVC, 528/859 (61.5%) of European Americans reported MVC-related pain outside body areas considered “whiplash-related” (head, neck, shoulders, and upper back), and 562/668 (84.1%) of African Americans reported pain outside such areas (unpublished data). Together, these data demonstrate that pain in body regions other than “whiplash-associated disorders” regions are very common after MVC and contribute substantially to overall pain-related disability. Thus, evaluating neck pain alone poorly characterizes the patient’s pain experience. Along with these increasing data that pain often occurs across many regions after MVC, and is frequently widespread, evidence has also continued to accrue that post-MVC pain often occurs in the context of other symptoms. For example, Dr. Michele Sterling and others have shown that pain after MVC, and PTSD symptoms after MVC are often comorbid [17, 44, 45], and depressive symptoms have also been shown to be frequently comorbid with post-MVC pain [6, 22, 35], along with a wide variety of somatic symptoms [36].

While patients experience coincident pain and somatic and/or psychological symptoms as part of one syndrome, most patients have each symptom type evaluated independently in compartmentalized, siloed clinical settings. An individual with persistent symptoms after MVC might, for example, see a psychiatrist for an evaluation of posttraumatic stress disorder and/or depressive symptoms, a neurologist for somatic symptoms labeled as “postconcussive,” and a physiatrist or anesthesiology pain medicine specialist for posttraumatic musculoskeletal pain. Similarly, research into biological mechanisms has also often been compartmentalized, with outcomes focused on one symptom domain or another. Better aligning neurobiological studies with the patient experience, by evaluating individuals according to multidimensional symptom cluster trajectory rather than symptom component, would
allow us to most accurately assess the neurobiological substrate of different multidimensional post-MVC syndromes.

Apr 4, 2021 | Posted by in PAIN MEDICINE | Comments Off on Neurobiological Mechanisms of Whiplash
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