Muscle twitching is a response when the electrolytes aren't doing their job. The 4 electrolytes are magnesium, potassium, sodium, and calcium. Generally, twitching is caused by a lack of magnesium....but with CF, low sodium levels can cause it too. I supplement with magnesium and I always have high sodium meals. I never get twitching anymore, though if I miss a couple days, I'll get them back.
When my twitching comes back, it always shows up first as an annoying eye twitch. UHG!