30 year old female with no significant past medical or family history presented with 2 month history of weakness , numbness and tingling in bilateral  hands and arms. She began to notice symptoms when she began a heavy exercise program as part of new employment in the police department. She stopped heavy exertion and started physical therapy with mild improvement. No symptoms were reported in the lower limbs.  Exam showed normal mental status and cranial nerves, 4/5 weakness of  in almost all right upper limb muscles, including a R.scapular winging, normal strength in the L.hand muscles except for 4/5 weakness in the L.interossei. Sensation to pinprick was impaired in the R.hand and forearm, and in the distribution of the L.ulnar nerve. Reflexes were absent in R.biceps and triceps, trace in L.biceps and triceps and normal in the ankles and knees. What is the localization? Differential diagnosis? (click here).