[Flexion myelopathy due to tic of neck]

A 22-year-old male developed a tic of neck-flexion at the age of 14. The tic occurred 40 to 50 times per minute on its peak at age 16. Since then he noticed the atrophy and weakness of his both upper limbs. His right leg became weak at age 22. On admission, neurological examination revealed tic of lip and neck, severe muscle atrophy and weakness of bilateral upper limbs, mild muscle weakness and spasticity of right lower limb and hyperreflexia in four limbs. Needle EMG studies revealed fibrillation, positive sharp wave and giant MUP in the biceps, triceps and first interossei muscles. There were no abnormal findings suggesting cervical spondylosis or disc herniation on neck roentgenogram and neck MRI in neutral position. Neck MRI in the ventro-flexed position showed a flattening of the lower cervical cord and a band-like isointensity lesion in the posterior epidural space at C4-6. This isointensity lesion was considered to represent a congestion of the internal vertebral venous plexus. These findings suggest that frequent neck flexion by itself causes the injury of the lower cervical cord through (1) over-stretching of the cord, (2) compression of the cord by dural sac, (3) arterior ischemia, and/or (4) stagnant hypoxia due to venous congestion. Flexion myelopathy may represent one of the most important mechanisms of cervical cord injury accompanied with involuntary movement of neck.