An overactive brainstem fed by the upper cervical nerves is the key problem. Changes in hormone levels act to trigger an episode but as world authority, Dr Elizabeth Loader explains: “Patients with menstrual migraine do not generally have hormonal abnormalities.”
At first this might seem a ridiculous statement. Dr Loder is referring to the fact that menstrual migraine, hormonal headache and menstrual related migraine have the same underlying problem that other chronic forms of head pain have, and that is an overactive brainstem (an area called the Trigemino-cervical nucleus or TCN).........NOT a hormonal problem.
While clearly hormone changes trigger episodes in many cases, the hypersensitivity of the trigeminal nerves is the underlying cause. An easy way to think of the interaction is that activity in the brainstem is like water in a cup. Most people at rest in a headache free state have a near empty cup. Menstrual migraine sufferers (along with all other chronic and recurrent headache sufferers) have a cup that is near full all the time. Typically a 'trigger' will then overfill the cup. These triggers can enter the trigeminal system in a number of ways via the lining of the mouth, nasal passage, small changes in blood vessels.
Oestrogen helps the body produce and absorb serotonin. Serotonin is what sets the height of the cup - its the barrier that this activity has to breach in order to give you a headache or migraine. So with your cup that is already near full, the rim shrinks down to a half cup, and now you are overflowing the cup and have a migraine.
The question is what is causing this overactivity, and this brings the top of the neck right into the middle of the frame. The nerves from the upper cervical spine are the only other ones joining the trigeminal nerves in this part of the brainstem and are the most common cause of this overactivity.
We know the brainstem is overactive because of two key pieces of information.
Firstly we see a marked change in a reflex that relates to this part of the central nervous system. Reflex activity, whether they are dulled, normal or excited inform doctors and researchers about how active the central nervous system is. In 2009 Varlibas and Erdemoglu studied a reflex that goes through the TCN. They found that menstrual migraine sufferers had “excited reflexes” compared to non-migraine controls, whilst not having a migraine. This supports the findings of other research in classic migraine, tension type headache, cervicogenic headache and cluster headache, indicating the TCN is always over active, and not just during headache episodes.
The second piece of evidence pointing to an overactive brainstem as the problem is that according to Mannix and Files (2005) the triptans have demonstrated some effectiveness as a pharmaceutical treatment. Triptans are a drug that help the brainstem absorb serotonin which raise the height of the cup or “turn down” the activity of the area in the brainstem responsible for referring pain to the head - the trigemino-cervical nucleus or TCN, and by doing so turn down or switch off headaches and migraines by stopping the referral process. For these to be effective in menstrual migraine there must be over activity in the TCN.
These studies confirm that the underlying process in menstrual migraine IS an overactive TCN. So where is this overactivity coming from? In a vast majority (over 80%) of cases it is a problem in the upper cervical spine that is causing constant input into the TCN and making it overactive. Using dedicated “headache specific” techniques this problem is assessable, treatable and self manageable in most people.