A 26-year-old woman had the right shoulder pain, weakness in her right arm, and noticed coldness in her right arm when it is down. On examination, she had droopy shoulder dominantly in right side, weakness and paresthesia in her right upper limb in the distribution of C8-Th1. The thoracic outlet compression tests were positive in her right side. Angiography of the right subclavian artery and brachial plexography under Allen's position revealed compression at the thoracic outlet. A cervical MRI revealed localized atrophy of the spinal cord (right side dominant) at the level of C5-6 vertebral body. Her spinal cord and dural sac moved anteriorly in cervical flexion. Droopy shoulder may be a risk factor of thoracic outlet syndrome and also flexion myelopathy. Double crush nerve compression of lower motor neuron at anterior horn of the cord and at the thoracic outlet may have accelerated the symptoms.