Sometimes people are diagnosed without an LP. But, I should think the majority do have one.
The point is that 95% of people with MS have what’s called ‘oligoclonal bands’ in their cerebrospinal fluid. So it helps a neurologist make a diagnosis.
An LP doesn’t usually hurt. They numb the area where the needle goes in. I remember it feeling very strange and kind of upsetting for some bizarre reason.
The general advice if you do have to have one is to drink lots of full strength Coke (bendy straw helps), because the sugar and the caffeine help, and to lay down afterwards for at least a couple of hours. These are to avoid a killer headache. not that I did either as I hadn’t been given any advice and didn’t get any side effects like a headache.
Another test that’s quite often used for MS diagnosis is Visual Evoked Potentials, where they map what is going on in your brain whilst you’re watching some weird images on a screen. That is non invasive so involves no pain or side effects.