Not to worry - this can all be very confusing!
First of all, you should read this article:
http://www.medhelp.org/health_pages/Multiple-Sclerosis/Paresthesias---Things-That-Go-BUZZ-in-the-Night/show/378?cid=36
Paresthesias are any abnormal sensations created by damaged nerves. The nerves can be damaged from the affected limb to the brain, essentially, but if you're experiencing symptoms in a particular area (I think they call these focal symptoms), you can guess that it's because of damage to the spine.
They include cold, burning, tingling, buzzing, feelings of pressure or numbness. The pressure thing is a little weird - I get this at the tips of both big toes. It feels like the foot is pressed against something, like the table, but when I look down they're not touching anything.
Twitching is a little different. I've never had a 'twitching' paresthesia. I have had actual twitching in various places. Mostly in areas that have a lot of small muscles, like the face, although my hands and my back also get into it. Twitching indicates nerve damage, but it can also be a sign of extreme anxiety. If you're not sure that it's twitching, put a hand on the area and see if it stops. Or if it continues! My twitches usually stop if I touch the area, but not always.
Anyway, twitching and spasticity are two different things. Spasticity manifests as unusual tightness and soreness of a muscle, but it actually is a resistance of the muscles to stretching.
http://www.medhelp.org/health_pages/Multiple-Sclerosis/Muscle-Tone-And-Spasticity/show/159?cid=36