Causes of nerve pain from the l. thumb-wrist, to the l. arm bicep, with a swollen 1 in. lump around extensor pollicis brevis, with a clear neck mri ?

It could be due to a: several conditions like De Quervain's tenosynovitis which is a painful inflammation of the tendons on the thumb side of the wrist, carpal tunnel syndrome affecting the tendon across the wrist, a radial nerve or other nerve entrapments, or an abnormal fluid collection like a ganglion cyst. See a specialist for electrodiagnostic testing or imaging studies.