How can i tell if my l side sciatic px is from piriformis syndrome or herniated disk? the pain intensity varies & at time only in my l low back/buttock. when i have leg pain to my left foot goes cold.

Sometimes : It's very difficult to differentiate between those two. A good physical exam and history necessary. Avoid positions that worse the pain. An MRI sometimes necessary to r/o hnp. Ice, rest and stretching exercises will improved a piriformis syndrome. Also the use of nsaids meds sometimes indicated. Can take long. I went through ps symptoms in the past. Good luck.

EMG: There are two options.First one is to do and emg(electromyogram)this test should tell you if the sciatica is due to a radiculopathy or due to others causes such as the piriform syndrome.Second one is more delicate and involves doing a piriform block(requires using an ultrasound guided inyection.Person doing it have to be expirienced using the ultrasound in that area.

Clinical exam: A good medical doctor will examine you and find out what is going on. Usually, straight leg raise testing will make it clear if this is from the nerve roots or from the nerve being pinched by the muscles (eg piriformis).