Whiplash and the Ascending Reticular Activating System
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Whiplash and the Ascending Reticular Activating System

It’s probably a safe generalization to assert that whiplash injuries caused by rear-end car accidents are typically undervalued. No matter what symptoms the patient presents with the diagnosis is misleadingly termed a “soft tissue” injury that “should resolve completely in six to eight weeks.” A new and growing body of medical literature sheds light on how whiplash injuries can cause injury to the ascending reticular activating system (ARAS).

What is the ascending reticular activing system? “The ascending reticular activating system (ARAS), also known as the extrathalamic control modulatory system or simply the reticular activating system (RAS), is a set of connected nuclei in the brains of vertebrates that is responsible for regulating wakefulness and sleep-wake transitions. The ARAS is a part of the reticular formation and is mostly composed of various nuclei in the thalamus and a number of dopaminergic, noradrenergic, serotonergic, histaminergiccholinergic, and glutamatergic brain nuclei… Direct electrical stimulation of the ARAS produces pain responses in cats and educes verbal reports of pain in humans. Additionally, ascending reticular activation in cats can produce mydriasis, [dilation of the pupil] which can result from prolonged pain. These results suggest some relationship between ARAS circuits and physiological pain pathways…”[1]

Is there medical literature which establishes a link between whiplash injuries and damage to the ARAS? There is: “We report on a patient who developed aggravation of excessive daytime sleepiness (EDS) concurrent with aggravation of an injured ascending reticular activating system (ARAS) following mild traumatic brain injury (TBI), demonstrated by follow-up diffusion tensor tractographies (DTTs)… A 42- year old male patient experienced head trauma resulting from flexion-hyperextension injury after collision with another vehicle from behind while stopped at an intersection. The patient lost consciousness for approximately 10 seconds and experienced no post-traumatic amnesia following the accident. The patient’s Glasgow Coma Scale score was 15. No specific lesion was observed on the conventional brain MRI performed at 10 weeks after onset. The patient complained of EDS after the head trauma and aggravation of EDS with passage of time…These studies suggest that injury of the ARAS could be a probable cause for the hypersomnia in patients with brain injury particularly TBI. In addition, analysis of the ARAS using DTT might contribute to understanding the prognosis of EDS. To the best of our knowledge, this is the first study to demonstrate an association between aggravation of EDS and worsening injury of the lower ARAS in patients with brain injury…In conclusion, aggravation of EDS concurrent with aggravation of an injured ARAS was demonstrated in a patient with mild TBI using DTT. These results suggest that evaluation of the ARAS using follow-up DTTs might be useful for patients who show change of EDS following brain injury particularly TBI.”[2]

“Diffusion-tensor imaging (DTI) is an MRI technique that uses anisotropic diffusion to estimate the axonal (white matter) organization of the brain. Fiber tractography (FT) is a 3D reconstruction technique to access neural tracts using data collected by DTI.”[3]

A forthcoming study draws a similar conclusion: “We found significant injury of the lower ventral ARAS in EDS patients with whiplash injury. These results suggest that diffusion tensor tractography (DTT) could provide useful information for detecting injuries of the ARAS following whiplash injury, in patients with EDS.”[4]

This class of injury should be considered in any serious car crash. Damage to the ascending reticular activating system explains why patients experience seemingly disproportionate symptoms. Diffusion tensor tractography is still not a mainstream diagnostic tool, but as this changes these injuries will be more frequently diagnosed. We’ve all seen instances where patients have not fully recovered––this new body of medical literature helps to explain why.

[1] Reticular Formation Wikipeida/https://en.wikipedia.org/wiki/Reticular_formation

[2] Sung Ho Jang, Hyeok Gyu Kwon, Aggravation of excessive daytime sleepiness concurrent with aggravation of an injured ascending reticular activating system in a patient with mild traumatic brain injury, Medicine (Baltimore) 2017 Jan 96(4): e5958 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5287967/

[3] fazeel, Dr. Ahmed Abdrabou, Diffusion-tensor MRI imaging and fiber tractography, Radiopaedia

[4] Sung Ho Jang, Seong Ho Kim, Young Hyeon Kwon, Excessive daytime sleepiness and injury of the ascending reticular activating system following whiplash injury, Front. Neurosci., doi: 10.3389/fnins.2018.00348 (Abstract)(May 2018)https://www.frontiersin.org/articles/10.3389/fnins.2018.00348/full