Final Report: Investigating the effect of high frequency stimulation over the greater occipital nerve onto trigeminal pain perception (Project 1)

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Subgrouping migraine patients by manual examination – a potential marker to predict treatment outcomes after greater occipital nerve block? (Project 2)

Project 1

Summary

The relationship between the neck and migraine is an enigma and has been neglected by many migraine researchers. Patients however report neck pain prior to or during a migraine attack. Since a block to the greater occipital nerve (GON-block) is effective for some primary headache patients, a functional connection between the occipital system (the neck) and the trigeminal system (the head) is likely. Blocking one system seems to block the other system. The question is whether stimulating one system stimulates the other system too. We followed the protocol in an experiment from a well-known neurophysiological institute in Mannheim and stimulated the first trigeminal branch (forehead) and the occipital system (GON) using electrical stimuli. We found that all participants showed a significant, gradual increase in pain perception over the stimulation site (sensitization of the trigeminal system). However, contrary to our hypothesis, there was no significant sensitization in the occipital system. After conducting many studies to investigate why we encountered difficulties with the study set-up, we concluded that this protocol is probably not suited for the trigeminal system.

Hypothesis vs. Findings 

We hypothesized that by sensitizing one system by stimulating it, the other non-stimulated system would also be sensitized. However, contrary to our hypothesis, there was no significant sensitization in the occipital system

Unanswered Questions 

We still believe that our original hypothesis is valid. Although most pain syndromes including headache share common features in neurological mechanisms, trigeminal pain has a strikingly prominent position which sets it apart from other pain syndromes. The first division of the trigeminal nerve seems to be set apart from the rest of the trigeminal system, leading to important pathophysiological and treatment considerations. The ophthalmic division of the trigeminal nerve may have an exclusive role in the trigemino-vascular system, and it is this physiological role that may render this system prone to respond to signals from the brain, and more specifically the limbic system.

Project 2

Summary

Since a block to the greater occipital nerve (GON-block) is more effective for some primary headache patients than for others, and since the GON-block is an invasive treatment, it would be useful to know in advance whether a patient is likely to benefit from this approach. Because the GON arises from C2, symptoms in the neck could be a predictive factor. We therefore grouped patients who were already scheduled to receive a GON-block according to their response from a manual assessment of the upper cervical spine into the three groups: no pain, local pain, and referred pain to the head. Overall, patients experienced a reduction of 1.9 headache days per month following the block. However, the groups differed significantly in the percentage change of headache frequency, with the no pain group showing the largest reduction. This data suggests that patients who are less sensitized will benefit more from the GON-block.

Hypothesis vs. Findings 

This observational study hypothesized that the response to manual joint palpation of the upper cervical spine in migraine patients will predict the efficacy of the GON-block. However, we found that patients with pain during manual palpation of the upper cervical spine did not benefit more from the GON-block. On the contrary, it was the group of patients who had no pain and were the least sensitive in the neck who had the best outcome.

Unanswered Questions 

The questions of the relevance of neck pain in migraine patients and the response to manual palpation of the upper cervical spine remain. In this study, we also assessed other predictive factors and additionally found that no headache on the day of the intervention and high pressure pain thresholds in the neck were predictive of better outcomes. However, this model only partially predicted outcome. Future research is required to find more predictive factors.

What this Research Means to You 

This research, which was possible thanks to the support of the Migraine Research Foundation, added another piece to the puzzle whether the neck has an influence on migraine symptoms, although it also raised additional questions. It is important to understand the relevance of neck pain so that patients can find the most effective treatment that is the least invasive and has the least side effects.