system
Given the following post, respond as if you're commenting on Reddit:
human
Why is forward, but not lateral, neck immobility a sign for meningitis?

When considering meningitis, doctors check if a patient can tilt his head forward. Why is the forward movement (chin to chest) an indicator for meningitis but other neck stiffness (inability to turn or tilt head to the sides) is not?

Disclaimer: of course the question arose from personal interest, but I have already been diagnosed by a professional as not having meningitis, so I'm not asking for medical advice. Just wondering what the physiology is.
gpt
Meningitis is an irritation of the coverings of the brain, called the meninges. Forward neck movement will cause the meninges to stretch and because they're irritated, it will cause pain. Lateral head movement doesn't cause a significant stretch on the meninges and won't cause the same neck pain. 

Think of it like this. The brain and spinal cord all share one continuous covering. When you lean forward you're effectively making that covering longer, which will stretch it. When it's irritated, that stretch causes pain.

Hope that answers your question!