Post Traumatic Headache - Don't Forget The Neck
Introduction
Headaches may have many different sources. They may originate from intracranial (inside the skull) pathology or present as referred pain from injury from other structures outside of the brain, including the neck and spine. This article will focus on headache that is referred from damage to the pain-sensitive structures in the neck, which may be permanent. This entity is known as cervicogenic headache, of which the most common lesion in the cervical spine is damage to the zygapophyseal joints. This entity should not be confused with primary intracranial pathology.
Post-traumatic headache may be part of a greater problem known as the post-traumatic headache syndrome, of which headache is only one symptom amongst many. Post-traumatic headache, however, can also be present without post-traumatic headache syndrome, as in the case of cervicogenic headache. Post-traumatic headache (or more appropriately post-traumatic head pain) is one of the most common complaints of people involved in trauma relating to the head and neck, particularly as a consequence of a whiplash injury. Of all the trauma that takes place, whiplash injury secondary to motor vehicle accidents has the highest incidence of insurance claims occurring in approximately 1:1000 population per year (Barnsley L., Lord S., Bogduk N. 1998). Most patients who are involved in whiplash injuries will resolve their complaints in approximately 12 months. It is estimated that about 80% of patients will be asymptomatic by that time (Radanov, D., Sturzenejgger, M., Di Stefano, G. 1995). It-is estimated, however, that approximately 5% of injured people remain severely affected after this form of injury with ongoing problems related to their injuries. Headache and neck pain are the most common complaint.
It has been suggested and shown in a recent paper that patients who are involved in whiplash injuries report headache as the dominant complaint. This headache has become known as cervicogenic headache. In this study, the source of the headache was traced directly to damage to the neck in approximately 53% of cases (Lord SM, Barnsley L, Wallis DJ, el al, 1994). Since the majority of post whiplash patients who seek legal advice are headache and neck pain sufferers, this review will concentrate mainly on this form of injury as the cause for chronic head pain.
Headache Post-Trauma Etiologies
There are multiple sources of head and neck pain that can occur as a result of trauma both inside and outside of the head. It should be noted that the brain itself is not a source of pain. The major structures inside the skull that produce pain are the dura, which is the thin coating of the brain, the venous sinuses, the blood vessels, and cranial nerves 1, 3, 5, 10 and 11. The major structures that are a source of headache outside the skull are the skin, the muscles, the tendons, the discs, and the joints and their capsules in the! neck region. Other structures which can be a source of pain in the head outside the brain are cervical nerves 1,2 and 3, and the thin layer of pain-sensitive tissues coating the bones in the head and neck (periosteum).
Pathophysiology
The exact mechanism by which pain in the head occurs is not known. Gross and microscopic abnormalities, including brain haemorrhage, occur in animals following carefully controlled head trauma. By approximating these findings with the few hemotoxicity reports that are available, it is clear that a variety of pathophysiological mechanisms may be operational to explain the constellation of symptoms that are seen! Recognition that trauma to the head and neck produces both biochemical, microscopic and gross structural changes offers the opportunity to explain the many symptoms that are seen. Recently, Packard and Ham (July 1997) discussed the similarity between the proposed neurochemical changes in migraine, flexion and extension injury, and those in experimental brain injury. They discussed how similar chemical reactions take place in flexion/extension injury and direct brain injury, that may include variations in extracellular potassium, intracellular sodium, increased calcium
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200
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Fig. 1 Movements of the trunk and head after a rear-end impact. Based on McConnell et al. [51]. The symbols represent reference points for the head (square), upper trunk (open circle), and lower trunk (filled circle). The numbers indicate time elapsed, in milliseconds, after impact. By 100 ms the trunk rises and compresses the neck from below. By 120 ms the head rotates backwards. By 200 ms elevation is complete and head rotation maumal. After 250 ms the head and trunk descend. By 300 ms the head rotates forwards, and reaches a maximum excursion by 400 ms, after which, restitution occurs.
and chloride, and excessive release of excitatory amino acids. They also discussed alterations in serotonin function and alterations in other neurotransmitters and endogenous opioids. They found that calcium magnesium levels and an increase in intracellular calcium, impaired glucose metabolism, abnormality in nitrous oxide formation of function, and alteration in neuropeptides, occurred in both types of head pain. It is clear, therefore, that although the underlying pathophysiology may be the same, the causation may be different depending on the type of trauma.
Clinical Diagnosis
The pain that persists post-trauma, as discussed earlier, may be due to many causes. The diagnosis of these different types of headaches may be difficult because of the number of different etiologies that may be present. However the most common and frequent cause of headache post-whiplash injury is pathology in the neck. This is due to direct damage to the joints of the neck known as the zygapophyseal joints, which are frequently disrupted in whiplash injuries. Recent studies (Bogduk, N., Yogandan, N. 2001) reveal that in a whiplash injury these zygapophyseal joints are damaged due to compression of the joints, rather than to a sliding injury or a strain (Fig. 1). The posterior compression of the inferior articular process into the upper articular surface is the cause of the pathology. Since these joints are pain-sensitive, when damaged they are a source of pain.
It makes sense to rule out cervicogenic headache prior to performing other investigations that may be unnecessary and of little value. As discussed earlier, cervicogenic headache is the most common cause of headache in this population. Other causes of chronic headache post-trauma include headache associated with minimal brain injury, or a variant of this, pain associated with TMJ pathology, and a brachial plexus like syndrome. These can usually be ruled out by further investigations and the clinical history. It is possible that two types of headache may co-e*xist, and it is postulated that the mechanisms for migraine post-trauma and post-traumatic headache may have similar underlying neurochemical changes although different etiologies.
Cervicogenic Headache
For many years there has been controversy regarding the clinical features of cervicogenic headache -that is, headache arising from traumatised structures in the neck. Cervicogenic headache shares many features with other forms of headache and is the one headache entity that can be diagnosed objectively and treated appropriately. The singular defining criterion for cervicogenic headache is that the pain is perceived in the head, but the source lies in the cervical spine. Diagnosis of cervicogenic headache therefore depends on establishing the source of pain in the neck using reliable and valid diagnostic techniques. Usually the patient experiences a generalized pain, which may be
Fig. 2 Tracings of serial radiographs of an individual undergoing a rear-end impact at 4 kph, with no head rest. Based on Kaoeoka el at. J60,61). At 44 ms after impact the cervical spine straightens and is thrust upwards by the rising trunk. By 110 ms it undergoes buckling into an S-shaped configuration, in which the lower cervical segments are extended and the upper segments are flexed. Al this time the anterior elements of Ihe lower cervical vertebrae arc separated (arrow head), while the articular processes are impacted (arrow). Subsequently, the upper cervical segments extend, and the cervical spine assumes a C-shape.
throbbing in nature, but is usually unaware of the source from which that pain may be originating. The difficulty with localizing head pain and neck pain is that the pain-sensitive structures in the head and neck converge at a single site called a nucleus in the central nervous system, which extends into the second and third cervical segments of the spinal cord (in the upper neck region). Regardless of where the pain is originating, when the nucleus is stimulated the patient will experience a generalized head pain and will be unable to pinpoint the actual source of the pain. The joints in the upper cervical segments at levels C-l, 2 and 3 are supplied by nerves that communicate with this nucleus. If there is trauma to these segments in the cervical spine, the nerves supplying the joints will relay pain to the nucleus and the patient will experience head pain and difficulty localizing the site of the pain. The patient will usually complain of pain relating to movements of the head and of the neck. Because the pain is diffuse and is similar to other types of head pain, the patient will in many instances complain of "migraine-like" symptoms. The problem, of course, is that with these common symptoms the uninitiated will immediately assume that the patient is suffering with "post-traumatic migraine", when in fact the patient may be suffering from a problem related to the cervical spine.
Diagnosis
There are very few areas in medicine where pain can be evaluated objectively. It is true that we use the visual analogue scales which have been shown to be effective and robust; however, it is invariably a subjective analysis and usually only part of an overall assessment of a patient with chronic pain. Physical examination and history are important in this type of injury, and usually patients will complain of some neck pain post-trauma. They will invariably complain of some
stiffness in the neck and may complain of pain in the suboccipital region, which is pain under the back of the head at the junction of the neck and the skull. Patients may also complain of spasm in their muscles, and the most common complaint is headache pain on movement of the neck. On physical examination the patient, when examined properly, will have tenderness in the neck region, which may be due to spasm, and on deep palpation may have tenderness around the zygapophyseal joints at the levels of C-2 and C-3. Palpation may reproduce pain in referred patterns (Fig.2). There may also be tenderness noted in lower segments of the cervical spine which will refer pain into the shoulder region but occasionally also into the head. The physical examination and history will point towards a differential diagnosis of cervicogenic headache. The radiological testing of the cervical region in patients who suffer with cervicogenic headache is usually normal. X-rays, CT scans and MR]'s cannot detect cervicogenic headache, as they are not sensitive enough to detect changes in the joints. The only reliable method for confirming cervicogenic headache is the use of diagnostic blocks. A diagnostic block is a procedure in which needles are used to deliver local anaesthetic under x-ray control to a joint suspected of being the source of pain. The idea behind a diagnostic block -is that if the joint is a source of head pain, then by anaesthetizing the nerve supply to that joint the pain should stop and the headache should go away. By testing the upper cervical joints in this way, a physician should be able to analyse the pain and decide whether the pain is coming from any of the joints involved. These diagnostic blocks are extremely helpful in the diagnosis of cervicogenic headache. They are positive as noted earlier in over 50% of patients who suffer with headache post-trauma, and the testing is important not only from a medical perspective, but also in the context of a medical-legal dispute to objectify the pathology. Because the patient has a number of nerve blocks, using both long-acting and short-acting anaesthetic, as well as a placebo, the accuracy of the test is extremely high. A positive result confirms that this is the source of the pain. It is unfortunate, however, that this test is expensive and it is difficult to undertake this test as frequently as it should be done due to lack of resources. There is a long waiting list for the procedure in the Province of Ontario, and similar delays are found across the country.
Fig. 3 A composite map depicting the characteristic distribution of pain emanating from the C2-3 to C6-7 zygapophyseal joints. (Modified from Dwycr A, April! C, Bogduk N: Cervical zygapophysea! joint pain patterns. 1. A study in normal volunteers. Spine 15:453-457. 1990.)'
There are no distinguishing features between the head pain of cervicogenic headache and other types of headaches, and the neck pain and the history of a flexion/extension injury may be the only clues that this is the entity that is implicated. The importance of a diagnostic block is that in many cases it establishes the legitimacy of the headache, and can also direct further management.
Treatment V
The diagnostic block, if positive, can dictate the type of treatment that may be helpful. For many cases there is a relatively safe surgical procedure which may assist to alleviate the ongoing chronic pain, and also the neck pain. The procedure, known as a rhizolysis, has been shown to be effective in helping the pain for a period of 12-18 months. A problem, though, is that the procedure needs to be repeated after 18 months. It should be noted however that the "turning off of the "barrage" of impulses from the damaged structures prevents long-term changes known as sensitization in the central nervous system, and may prevent the development of chronic, non-malignant head pain.
Other interventions may be helpful in controlling the pain. They include short term relief with physiotherapy, and the judicious use of pharmacological interventions. The group of drugs known as the triptans may be helpful for the acute exacerbations of this headache (Gawel, M., Rothbart, P., Jacobs, H., Headache 1993).
Conclusions
Until the work of Bogduk and his associates, cervical zygapophyseal joint pain as a source of headache was ignored by physicians, especially neurologists and orthopaedic surgeons. Because they were unaware of this connection, they were not prepared to accept the entity. Unfortunately, this ignorance persists despite irrefutable evidence to support this diagnosis. Using comparative local anaesthetic blocks, Bogduk showed that the prevalence of cervical zygapophyseal joint pain has been found in 54% of patients with chronic neck pain after whiplash injury, and that this presence has been confirmed using placebo-controlled triple blocks (Lord, S.M.. Barnsley, L., Wallis, D.J., Bogduk, N. 1996). Moreover, headache after whiplash was also found in the majority of patients to be traced to a painful C-2, C-3 zygapophyseal joint (Lord, S.M., Barnsley, L., Wallis, D.J., Bogduk, N. 1996). The seminal work by Bogduk and associates mapped out the referral patterns of pain (Fig.3) including headache, when these joints at the levels of C-l, 2 and 3 were stimulated and reproduced headaches (Dwyer,A., April, C., Bogduk, N. 1990). Other researchers in the field also reproduced similar patterns. It is accepted without a doubt in the pain field that the cervical spine can be a source of headache and is the most common cause of headache following flexion/extension injuries. (Sukui, S., Ohseto, K., Shiotani, M., et al 1996)
Unfortunately, many physicians are not aware of this entity and completely ignore the cervical spine as a source of head pain. The significance of ignoring this entity is that treatment towards the underlying pathology is also ignored and the patient continues to suffer as a result of the misdiagnosis. It is imperative to be aware of this entity in a patient presenting with headache following extension/flexion injury because of the possibility of objectively making a diagnosis.
C2-3
Post-traumatic headache should not be confused with post-traumatic headache syndrome. Post-traumatic headache is a distinct entity that occurs due to either intracranial or extracranial pathology. The final common pathway is the same, however, but the etiologies may be different. The most common cause of ongoing, chronic, non-malignant head pain post- trauma is cervicogenic headache, and this entity should be ruled out as part of a work-up of a patient suffering with chronic, non-malignant post-traumatic head pain. While these patients usually do not have life-threatening problems, their problems have a severe morbidity and disability in the long run. Misdiagnosis, accusations of malingering, and accusations of psychological problems causing the pain, are unethical and scientifically unfounded in the present time given the state of knowledge we have regarding the pathophysiology of head pain. In a study done by Wallis el al., it was shown that the psychological effects of chronic headache and neck pain were reversed when the pain was treated (Wallis, B.J., Lord, S.M., Bogduk, N. 1997). It behooves the medical profession to investigate patients who suffer with chronic, non-malignant head pain post-trauma, in an ordered fashion. Patients who are seen in the acute phase should have all the most likely diagnoses of head pain that are life threatening, ruled out. Most of the headache pains that are seen by the medical-legal profession are persons suffering with long-lasting chronic headaches and neck pain. It is a sad reflection on the medical profession that, despite our present state of knowledge, the myth of headache as being a psychological problem post-trauma, continues to be perpetuated in the profession. It is at this time unethical -not to investigate a patient thoroughly for the most likely cause of headache post-trauma, allowing the patient to suffer in chronic pain and to not be treated appropriately. It is timely that the legal and medical professions understand the pathophysiology and significance of chronic head pain post-trauma, and appreciate that this is a real medical problem with real pathophysiology that cannot go away untreated and undetected. It is hoped that we will move forward in the future, such that patients suffering with this entity will be allowed to be investigated further and not given the stigma of a psychological disorder.
References
Barnsley, L., Lord, S., Bogduk, N., The Pathophysiology of Whiplash, in Malanga, G., ed. Cervical Flexion and Extension/ Whiplash Injuries. Spine: State of the Art Reviews Volume 12 Philadelphia, PA: Hamley and Belfast 1998:209-242.
Bogduk, N., Yoganandan, N., Clinical Biomechanics 16(2001)267-275.
Dwyer, A., April, C., Bogduk, N., Cervical Zygapophyseal Joint Pain Patterns One: A Study in Normal \blunteers. Spine 1990 15:453-457.
Gawel, M., Rothbart, P., Jacobs, H., Headache 1993; 33:96-97.
Lord, S.M., Bamsley, L., Wallis, D.J., et al., Third Occipital Headache Prevalence Study Journal Neural Neurosurg Psychiatry 1994; 57:1187-1190.
Lord, S.M., Barnsley, L, Wallis, D.J., Bogduk, N., Chronic Zygapophyseal Joint Pain after Whiplash: A Placebo Control Prevalence Study. Spine 1996; 21:1737-1745.
Lord, S.M., Bamsley, L, Wallis, D.J.,
Bogduk, N., A Randomized Double Blind Control Trial of Percutaneous Radiofrequency Neurotomy for the Treatment of Cervical Zygapophyseal Joint Pain, . in abstracts Eighth World Congress of Pain, August 17-22 1996, Vancouver, British Columbia, Canada. Seattle: ISP Press 19963AV2
Packard, R.C., Ham, L.P., Headache 1997;37:142-152.
Radanov, D., Sturzenegger, M., Di Stefano, G., Long Term Outcome after Whiplash Injury: A two-year follow-up considering features of injury mechanism and somatic radiologic and psychosocial findings. Medicine 1995; 74:281-297.
Sukui, S., Ohseto, K., Shiotani, M., et al., Referred Pain Distribution of the Cervical Zygapophyseal Joints and Cervical Dorsal Rami. Pain 1996,68:79-83.
Wallis, B.J., Lord, S.M., Bogduk, N., Resolution of Psychological Distress of Whiplash Patients following Treatment by Radiofrequency Neurotomy: A Randomized, Double Blind, and Placebo-Controlled Trial. Paw 73 (1997) 15-22.
Howard Jacobs, M.D., L.R.C.P. & S.J., D.A.A.P.M., is a Board Certified Pain Medicine Physician and Medical Director of The Pain Institute in Toronto.