3 weeks ago i developed numbness side of thigh from crotch down to knee. has not subsided. will this cause permanent damage? being worked up for ms.

Hard to say: This sounds like a localized problem to the side of the thigh on one leg. If that is the case, one has to consider compression (ie. A herniated disc) or irritation of the nerve root. An MRI scan would help to differentiate. Sounds like you are working with a neurologist who is doing the work-up for ms. This certainly is a consideration. As to whether this is permanent, it depends on the cause.

Suspect benign: This does not at all sound like Multiple Sclerosis, and likely represents a problem with a pelvic issue affected a nerve in the lumbosacral plexus. Imaging of retroperitoneal areas, and an EMG may help pinpoint cause, and also help with prognosis.