Rheumatoid arthritis commonly involves the neck (cervical spine). Studies have shown it to occur in 83% of patients  within 2 years of disease onset. 
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Neck pain in a patient with rheumatoid arthritis can be a warning of serious neck problems. Potentially life threatening myelopathy (spinal cord compression) can result from instability in the cervical spine.
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Signs and symptoms of myelopathy can include numbness, weakness and clumsiness in the hands and/or feet, unsteady walking, poor balance, muscle spasm, and loss of control of the bladder and/or bowel.
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Instability  is most commonly seen between the first cervical vertebra (atlas) and the second cervical vertebra (axis) and is called atlanto-axial instability.
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Instability can also occur between the skull and the first cervical vertebra (cranial settling) or below the second cervical vertebra (subaxial instability).
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The formation of a dense fibrous tissue unique to rheumatoid arthritis known as pannus can also cause myelopathy.
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The goal of treatment is  to remove pressure on the spinal cord and obtain stability. This can only be done surgically. Suuccessful surgery will prevent progression of the signs and symptoms of myelopathy which often resolve completely. 
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Click here for an example of atlanto-axial instability.