A 26-year-old infantryman developed right hand and arm weakness while deployed to Iraq. Extension of the right second digit worsened over 2 weeks, followed by difficulty extending digits 3–5 over the following weeks. He reported muscle twitching in the right upper extremity over the same period, and that his thumb would lock or cramp in an opposed position during use. He denied pain, motor, or sensory symptoms in other extremities. Nine months prior, he sustained an injury while parachuting during airborne school, resulting in a concussion, headache, and neck and back pain, but no weakness.