resulting in demyelination, a process where the outer protective layer of the nerve (myelin) is damaged, and damage to the axon (the part of the nerve cell that transmits electrical nerve impulses). Demyelination and axonal damage can result in symptoms including pain, abnormal sensations, such as tingling and “pins-and-needles”, and muscle weakness. The most common manifestations of this non-compressive nerve damage include loss of the ability to extend the wrist (wrist drop) or move the toes or ankle upward (foot drop), as in the motion used for walking
Nerve compression (also called entrapment) can occur early in the course of RA, as changes take place in joints, resulting in direct pressure on nerves located in proximity to joint structures. The most common example of this is carpal tunnel syndrome, a condition that affects as many as two-thirds of RA patients. In carpal tunnel syndrome, inflammation affects the tendons and ligaments that surround the median nerve, which runs through the carpal tunnel in the wrist into the thumb side of the hand. Inflamed tendons and ligaments compress the nerve producing stinging pain, numbness, and tingling, affecting the first three fingers and the thumb side of the hand. Pain and abnormal sensations are made worse by repetitive movements and nerve symptoms may even involve the forearm and upper arm