Cervical spondylosis is the most common disease causing arm numbness, but the cause of arm numbness is not necessarily cervical spondylosis. There are many causes of arm numbness, such as thoracic outlet syndrome which can compress the brachial plexus nerve and cause arm numbness, and is the most important disease to identify with cervical spondylosis.
Also diabetic peripheral neuropathy, peripheral neuritis, peripheral neuritis, spinal cord cavitation, and menopausal syndrome can likewise cause numbness in the arm.