paresthesias, headache, ? CNS infection

My son, a 26-year-old male, 8 weeks ago developed tingling/numbness up back of left leg after a 3-mile run. Over next few days, numbness went down leg to toes and up the left side of body including arm and left side of face up to temple.  No other positive neurological signs.  CT scan of head normal; MRI brain normal;  MRI neck showed syrinx at C6-7, now felt by neurologist and neurosurgeon to be an asymptomatic incidental persistent central canal; Lyme negative.  After two weeks, developed low backache, neckache, mild knee ache--all of which come and go. Now, after 8 weeks, developed severe hat-band like and base of skull headache/pressure, and the paresthesia spread though his entire head, right side of face and down right side of body--so total body tingling now, along with pounding headache.   Visual evoked potential testing negative; EMG being done tomorrow.  Neurologist suspects MS or complicated migraine??  Now beginning to look and feel "sick!"   Can they be missing something more ominous--? some kind of CNS infection?  Should he be having more invasive testing?  Thank you so much for your time and help.