Anterior displacement of the spinal cord on flexion views in a patient with unilateral arm weakness

A 21-year-old man presented with a 1 year history of progressive right arm weakness and muscle wasting. The weakness was gradual in onset, initially beginning distally with weakness of wrist flexion; however it spread to involve the whole of the right arm. There was no weakness in the left arm or lower limbs and no other neurological symptoms. He took no regular medications, and did not have any significant past history. He worked in the freezer section of an abattoir. On examination, there was atrophy of the right pectoralis major, triceps, flexor and extensor muscle groups in the forearm, abductor pollicis brevis and all interossei muscles. There were fasciculations of the right triceps but also fasciculations evident in the left triceps muscle. There was moderate weakness across all muscle groups in the right arm, however the weakness and wasting was more marked in the hand and forearm muscles. Froment’s sign was positive in the right hand. Reflexes were normal and symmetrical. Sensation, proprioception and coordination were normal. Full blood count, electrolytes, serum protein electrophoresis and cerebrospinal fluid analysis were unremarkable. Nerve conduction and electromyography showed chronic partial denervation in the right C5 to T1 innervated muscles maximal in the lower myotomes, with minimal active denervation. These findings were consistent with chronic neurogenic changes in spinal roots or anterior segments. He underwent an MRI of his cervical spine in neutral and flexed positions (Fig. 1).