The Craniocervical Junction and Headache Disorders

 

Headaches disorders are amongst the most common conditions that people seek treatment from a doctor. While most people will experience a headache of some form,  there are those who develop chronic and repetitive bouts with headaches of different types.

Unlike people who may struggle with an occasional stress headache or feel the effects from an alcohol induced hangover, people with these chronic headaches have a neurological disorder. These headache disorders can stem from:

  • Migraines
  • Cluster headache
  • Post-traumatic/Post-concussive headache
  • Chronic pain/Temporomandibular joint disorders
  • Tension headache
  • Chronic daily headache
  • And more

Each headache has unique characteristics that help to make an effective diagnosis for effective treatment. However, when we look at the reality of a daily patient interaction, we see that people with these headache disorders can have traits that overlap. (Remember this point because this is something I’ll come back to later)

That makes these headaches  extremely burdensome on the patient, but it can also be challenging for a doctor or therapist to find effective solutions. This is particularly challenging considering the rise of medication overuse headaches as a clinical entity in 2004.

Medication overuse headaches were once classified as rebound headaches because of the way headaches could come back with a vengeance after the pain-relieving effects of a medication wore off. It became re-classified in part due to the alarming number of patients showing a regression in their headache symptoms after prolonged and frequent use of medication. While the physiology of this disorder is widely unknown, it does show characteristics of physical dependency as seen with drug withdrawals.

As drug therapies become less effective for this subset of headache patients, there has become a growing need to identify non-pharmacologic strategies to help patients with headache disorders. For many of these patients, a possible solution might lie in the neck.

Headaches and the Cervical Spine

The concept of neck problems contributing to headache disorders isn’t new. Cervicogenic headache is a term coined in 1983 to describe patients suffering from simultaneous head and neck pain [1]. The term has grown to have diagnostic criteria that include:

  • Single sided head pain radiating from the top of the neck
  • Aggravation by specific neck positions
  • Reduced upper cervical motion or painful range of motion
  • Presence of muscular trigger points
  • Normal imaging
  • Unresponsiveness to pharmacologics

Cervicogenic headache does have a contentious history as a distinct clinical entity. Critics have argued that the soft nature of the diagnostic criteria. In the past, cervicogenic headaches seemed to be diagnosed by the effectiveness of cervical spine therapies in relieving the headache. You can see how this complicates the study of these headaches as a distinct clinical entity. In recent years, nerve blocks or ablations in targeted areas of the cervical spine have been used to determine if the cervical spine is the cause of the headache, but these also require more invasive procedures to make an assessment [2].

Headaches originating from the neck seems to have the biggest role in chronic headaches that begin after a concussion or whiplash. Headaches that emerge after these injuries are commonly classified as cervicogenic headache.The neurophysiologic effects of a concussion tend to disappear 7-14 days after the trauma but the ligament and muscle injuries from a head injury can persist leading to a default diagnosis of cervicogenic headace. The study of cervicogenic headache has revealed quite a bit about the physiology of how the neck can play a role in head pain, even those associated with migraine headache [3].

One problem with this idea is that fact that a traumatic injury can sometimes lead to patients who have never suffered a migraine before, can display migrainous symptoms after an injury [4]. This is also complicated by the fact that conservative cervical spine interventions like spinal manipulation and manual therapy appear to be effective in cervicogenic headache [5], but not in migraine [6] in clinical trials.

What do these headaches have in common? How are they different? Can we use their similarities to develop effective treatment strategies for headaches that are resistent to medications?

The Physiology of Headache Pain

There’s a common source for pain related to the head and neck. That source is a bundle of neurons located in the brain stem called the trigeminocervical nucleus (TCN). This nucleus is a hub for nociceptors in the brain. Nociceptors are receptors that transmit information about noxious stimuli to the brain, usually in the form of tissue injury.

While the feeling of pain is far more complex than the sheer amount of nociception your brain receives, for the sake of simplicity in this article, we will say that nociceptors are fibers that carry pain signals. Your TCN is a major player in head AND neck pain.

Head and neck pain pathway

This area in the brain stem is like the Grand Central Station for all of the pain sensing fibers in the head and neck. From the trigeminal nerve you have pain sensing fibers from the face, jaw, teeth, arteries, and meninges, while the neck has fibers from the joints, ligaments, muscles, and skin coming from C1, C2, and C3 nerve roots. All of these fibers converge onto TVN which has to decide if it’s worth going up to the big kahuna at the top of the brain called the cerebral cortex.

For neurovascular headaches like migraine and cluster headaches, it’s suspected that the pain carrying fibers from the arteries in the brain or the outer covering of the brain called the meninges getting irritated by pulsing arteries. These fibers are carried to the  TVN by the trigeminal nerve. For cervicogenic headaches, it’s suspected that the pain generators are coming from the muscles, nerves, or joints from the upper neck.

These overlapping structures allow for some of the referred pain patterns seen in migraine patients expressing neck pain, and also for cervicogenic dysfunction to lead to headaches. It also means that if 2 pieces of anatomy share a neurological pathway, then sometimes treating one area can lead to relief in another.

Interventions in the Cervical Spine and Headache Outcomes

So we know that the convergence of these neural fibers allows for some overlap of pain sensation regardless of the type of headache. What does the research say about treating headaches with cervical spine interventions?

The answer seems to match what you think it would be.

For cervicogenic headaches, recent studies seem to support the idea that addressing the neck with spinal manipulation can be helpful and even provide some relatively long term impact. A 2016 paper showed that upper cervical and thoracic manipulation helped cervicogenic headache patients at 3 months compared to exercise and mobilization [7]. A review paper of several studies on cervicogenic headache and manipulation seems well in favor of treating the neck compared to controls [8].

For migraines, the evidence isn’t so favorable for manual intervetions. There aren’t that many clinical trials to look at, and the ones that are available appear to show no effect [9]. From a pathophysiological standpoint it makes sense because they seem to be clinically distinct entities. However, the clinical experience of people like myself who practice in an upper cervical model of chiropractic have had a much different experience.

There is some evidence that suggests that cervical spine problems may be present as a sub-type of migraine patients [10]. There is also evidence that greater occipital nerve blocks [11] and non-invasive vagal nerve stimulation in the neck [12] can decrease the frequency of headache days and may effectively abort a migraine attack.

A 2016 study by Woodfield studied 11 patients with chronic migraines showing improvements in migraine frequency while receiving a vectored correction to the atlas vertebra [13]. The study also showed some significant effects in intracranial compliance in patients with cerebrovenous drainage abnormalities.

Case Study on NUCCA atlas procedure on venous drainage routes in a migraine patient.

While the concept of cerebrospinal venous abnormalities have been a controversial topic in multiple sclerosis, it may provide insight into some patients with chronic migraine. Multiple studies have documented venous drainage abnormalities in migraine patients and even mTBI, but the significance behind these observations are unknown [13] [14] [15].

Where To Go From Here?

There’s still a lot to learn about the anatomy and physiology of headache disorders. When you consider that migraine headaches are the most common neurological disease in the world.

Predicted research dollars compared to diseae burden

Lots of work needs to be done to understand what treatments will work for which patients, but there’s still some hope that treating the neck may be a key strategy to help people with chronic headache disorders.

 

 

 

Rectus Capitis Posterior Minor in Headache Disorders

Neck muscles have been a source of suffering for patients for a long time. In recent years, one neck muscle in particular is getting a lot of attention in the world of head injury.

Meet the rectus capitis posterior minor (RCPMi)

Image Credit: Duke Univeristy Learning labhttps://web.duke.edu/anatomy/Lab01/Lab2_new2014.html

Yep. It’s that tiny little muscle deep in the middle of your neck. It connects from the top bone in your neck called the atlas, and it connects into the head via connective tissue called the myodural bridge. But more on that later.

All in all, the the RCPMi is not much bigger than the end of your pinky finger, but it’s capable of wreaking havoc on people with neck problems including concussion.

Headaches, Trauma and the Rectus Capitis Posterior Minor

The RCPMi has been considered a muscle of importance in chiropractic literature for a long time. It’s only been a recent phenomenon where more mainstream medical science has started to look at its role in headaches and trauma. Two such studies examined the RCPMi in 2016.

The first study was published in the American Journal of Neuroradiology. They saw that patients with atrophy in the RCPMi had more severe concussion symptoms and a worse prognosis. You can check out the abstract here:

Effect of the suboccipital musculature on symptom severity and recovery after mild traumatic brain injury

The second study was published in the presigious headache journal, Cephalgia. The authors found that patients with chronic headache tended to have more hypertrophy in the RCPMi than controls. You can check out that abstract here:

Correlation between chronic headaches and the rectus capitis posterior minor muscle

In case you weren’t paying attention, you should probably find those 2 outcomes to be a little strange.

On one hand, having smaller RCPMi had worse outcomes with concussion symptoms. On the other hand, having larger RCPMi was more likely to be associated with chronic headaches.

Granted we are dealing with 2 different conditions, but one of the biggest problems with chronic concussive symptoms is chronic headache. It would seem like there should be some overlap. What gives?

How Can That Small Muscle Cause So Many Problems?

There’s a few unique things about these muscles.

  1. The RCPMi does not connect into bone like most muscles do. It connects into a piece of tissue called the myodural bridge. That means it has a direct link into the outer covering of the brain which is known to be very sensitive to pain.
  2. The RCPMi is too small to provide much in the way of meaningful movement of the head and neck. Inside the belly of this small muscle are abnormally large amounts of prorioceptors called muscle spindles. Proprioceptors help provide feedback to the brain about joint position and movement.
  3. Changes in the RCPMi can deform the myodural bridge which changes movement in cerebral spinal fluid. Abnormal movement of this fluid is associated with headache.

So as you can see, even though the RCPMi is small it carries a large baggage of neurology with it.

What’s Happening in Headaches and Concussions?

This is where things get a little interesting, because we don’t really know how this muscle is causing problems. More evidence is showing that there is a correlation between this muscle and headaches, but we don’t really know anything about causation yet.

With that being said, this is mostly just speculation on my part, so here it goes.

In my office we are always striving to create symmetry in the structural positioning of the head and neck.

When the head and neck shift, it creates asymmetrical force production in the suboccipital muscles. Image Credit: Daniel O. Clark uppercervicalillustrations.com

When there is an injury like a trauma or whiplash, you create injury in some of these small muscles of the neck. When these muscles are injured, the brain loses some critical feedback mechanisms that helped to maintain proper positioning of the head and neck.

The injury also creates asymmetrical tension on the myodural bridge. This abnormal tension on the dura stimulates the sensitive pain receptors in this tissue leading to head and neck pain. There have even been cases where cutting this muscle can relieve a patient of chronic headache.

That same tension on the dura may also be creating abnormal flow of cerebral spinal fluid which may lead to chronic effects of brain physiology.