Idiopathic intracranial hypertension (IIH) is a disorder of pressure inside the head.
Obstructive sleep apnea (OSA) is a sleep breathing disorder.
Many of my patients are surprised to learn that these two issues are connected. (I was surprised to learn this myself years ago as a trainee.)
Let's start with breathing. The basics of respiration are that we breathe in oxygen and we breathe out carbon dioxide.
Sleep apnea is a breathing problem. Usually patients snore and occasionally the snoring turns into a pause of the breathing.
Everyone intuitively understands that this causes a drop in the blood oxygen level. What we tend to ignore is that this causes a brief rise in the blood carbon dioxide level, too.
The carbon dioxide is the main problem here. Carbon dioxide will cause a shift in the pH of your blood, and the brain particularly does not want any shift in the pH. So, the brain has a mechanism to dilate blood vessels to increase blood flow and flush out that extra carbon dioxide.
The skull is a rigid, fixed space. If you increase the volume of blood then some basic physics tell us that the pressure is going to go up.
It works both ways actually. When I do lumbar punctures, I have to be careful to make sure the patient doesn't hyperventilate or hold their breath because it will affect the pressure measurement. Oftentimes, once the pressure has been measured, I will ask the patient to take a few deep breaths and amaze the medical students with how much a few breaths will reduce the pressure.
So, what does this mean for IIH patients?
I think it is worth asking every IIH patient about OSA symptoms. A simple 10 question survey, the Berlin Questionnaire is a great screening tool.
If patients have symptoms suggestive of sleep apnea, then I'd recommend a sleep evaluation. If they do have confirmed sleep apnea then treatment would be helpful. Treatment options include a CPAP mask which blows the air in and keeps patients breathing, or dental appliance that holds the jaw open enough to keep breathing.
In some patients the sleep apnea seems to be the main issue, and once that is taken care of, they may not need any further treatments.
So, in conclusion, sleep apnea causes carbon dioxide levels to go up and that causes pressure in the head to go up. IIH patients should be evaluated for OSA when appropriate and treated. Sometimes it is the main treatment that they need.