In part 1 we explained the underlying cause of menstrual migraine, as it is with other chronic headache and migraine types, is an overactive part of the brainstem called the trigemino-cervical nucleus or TCN. At the heart of this over activity is the interconnection in the TCN between the nerves from the upper part of the neck, and the nerves thatsupply the head and face. Hormones simply make it easier for this overactive brainstem to cause migraines. Let me explain further.
Oestrogen plays a critical role in the production of serotonin and also helps the brainstem to absorb serotonin. When oestrogen levels drop around day 1 of the menstrual cycle the levels of serotonin drop as well.
Changes in the level of serotonin have a significant impact on headache and migraine. In fact the medications from the triptan family (e.g. Imigran, Naramig, Maxalt, Relpax, Sandomigran) are effective because they make the brainstem absorb more serotonin.
So what does serotonin do?
Increasing the levels of serotonin decreases activity in the brainstem, and stops activity “spreading” to the extent where it “switches on” the nerves of the head and face causing pain – a headache or migraine. It’s not just having more serotonin though. Too much as well as not enough will cause problems because serotonin also impacts on the blood vessels on the lining of the brain.
A decrease in Serotonin will cause these blood vessels to dilate, contributing further “information” to an already overactive brainstem. Added to the loss of control of this over activity and it is not hard to see why the nerves in the head are “lit up” causing a migraine.
Around mid cycle when oestrogen levels rise, serotonin levels rise causing blood vessels to constrict. This mechanical input from constricting vessels is enough in some people to trigger another headache, similar to the day 1 migraine, but commonly far less intense and often not migrainous in nature.
The fluctuation in oestrogen and hence, serotonin is no different in menstrual migraine sufferers and non-sufferers. This has prompted leading expert in menstrual migraine Elizabeth Loder to say:
“We must look at other factors (other than hormones)…………. Abnormal central nervous system response to normal fluctuations in hormones is the likely underlying cause of menstrual migraine”. (2001)
Menstrual migraine is treatable, not by trying to treat hormones, but trying to treat the underlying activity in the brainstem. The upper cervical spine has the most significant input into the brainstem and in 80% of cases the usual pain of migraine and headache is able to be “switched on” by selective and specific pressure applied to the upper part of the neck. If this reproduced pain eases as we sustain the pressure, then treatment will be successful in 90% of cases.
Roger O'Toole is the Director and Senior Clinician of the Melbourne Headache Clinic and has over 10 years experience as a physiotherapist.