As neurologists, headache is one of the pain disorders we see most often, especially Dr. Mueller who is a headache specialist. Most patients with headache have episodic symptoms and go back to feeling normal between attacks. But some suffer from headaches almost every day, and even when they don’t have pain, they still don’t feel normal. There’s fatigue, brain fog, dizziness and other symptoms that their doctors don’t seem to understand.
Pain is a stressful experience, and the autonomic nervous system (ANS) orchestrates the stress response, including changes in blood pressure, heart rate, and alertness. But like any good conductor, a properly functioning ANS knows when to decrescendo. Perhaps as headaches become more frequent, and the ANS is repeatedly called to action, it begins to have trouble returning to a resting state. Could changes in the ANS cause the other non-painful but debilitating symptoms that can accompany chronic headache?
With Dr. Mueller in the lead, we studied 34 people with headache who had undergone autonomic testing in our lab, comparing those with chronic headache to those with episodic headache. The testing performed at the Mount Sinai autonomic lab has several parts as described by PAIRED Project alum, Alyha Benitez, in this video. We can use the results of our autonomic testing to describe autonomic function and dysfunction in different ways. One way is to calculate a summary score, called the Composite Autonomic Severity Score (CASS), which takes into account all the test results. We can also calculate other scores that look at individual parts of the ANS, for example BRS-V (which stands for vagal baroreflex sensitivity). BRS-V measures changes in heart rate in response to stress which is controlled by the very important autonomic nerve known as the vagus.
What did we find? Well, not surprisingly, people with chronic headache were far more likely to experience symptoms of fatigue, cognitive impairment and POTS. But let’s look at the results of the autonomic tests, which are summarized in the figure below.
The dark striped bars represent the number of people with reduced BRS-V. Among people with episodic headache (on the left), the dark striped bar is very low indicating that very few have abnormal BRS-V. But in people with chronic headache (on the right), the dark striped bar is much higher, indicating that more of them have abnormal BRS-V. We saw a similar pattern when we looked at the CASS score.
The presence of non-painful symptoms such as fatigue and cognitive impairment were also associated with autonomic dysfunction. The full results were published in Frontiers in Human Neuroscience in March. For more about headache and autonomic dysfunction also check out our review article in the journal Headache which has a cool figure describing overlapping mechanisms in POTS and migraine.