Must an emg test for periperal neuropathy include both a test of an arm and leg to be valid? i was told i have pn based on legs only.

No: Peripheral neuropathy may only manifest in one limb -- that's the only area that would need to be tested. Tests may be more extensive if the symptoms are also more extensive.

Legs can be enough: While some of the more sensitive measures of neuropathy do require comparing arm and leg responses, if the neuropathy is advanced enough the diagnosis can often be made with the legs alone.

Often when testing: For neuropathy that may be diffuse or peripheral in more than one extremity the nerve study and EMG will include the legs first as. Many types of diffuse peripheral neuropathy show up in the feet before they show up in the hands.