I get similar but totally in top of legs to my knees.
My cause is intolerance to anything with aspartame and artificial sweeteners. Also certain hard tablets... depending what the bulking agent is or the coating on the tablet..
Ie over christmas I decided to try drambuiee and diet coke just to test out. Aspartame intolerance had been missed off my records , for 8 years I wasnt told. My legs went totally off the scale with feelings like constant muscle cramps/pulling and absolute chronic twitching.
I have also now decided yo stop taking my final cancer drug option as they affected my legs (and a lot more). I decided. Quality of life now comes before quantity of life.
Could be neuropathy etc but I would really consider hat foods you eat and drink, are you getting sufficient vitamins, and whether you intaking aspartame or any recent tablet / meds changes