Veteranclaims’s Blog

October 9, 2011

Time Window For Motor Nerve Repair

Filed under: Uncategorized — veteranclaims @ 7:51 pm

Full article at: In Reversing Motor Nerve Damage, Time Is of the Essence: ‘Wait and See’ in Injuries Like Carpal Tunnel Syndrome May Miss a Window for Recovery

ScienceDaily (Oct. 3, 2011) — When a motor nerve is severely damaged, people rarely recover full muscle strength and function. Neuroscientists from Children’s Hospital Boston, combining patient data with observations in a mouse model, now show why. It’s not that motor nerve fibers don’t regrow — they can — but they don’t grow fast enough. By the time they get to the muscle fibers, they can no longer communicate with them.

The study, published in the November issue of the Journal of Clinical Investigation (online Oct. 3) has immediate implications for patients with motor nerve injuries, including carpal tunnel syndrome, cubital tunnel syndrome, nerve damage caused by surgery and brachial avulsion injuries: Time is of the essence in repairing nerve damage.

“There’s a clock ticking, and if you’re too late, the muscle cannot be functionally reactivated,” says Clifford Woolf, Ph.D, senior investigator and director of the Program in Neurobiology and F.M. Kirby Neurobiology Center at Children’s Hospital Boston. “If there’s muscle weakness, waiting six months to see if it gets better or worse before intervening may not be the best idea.”

Studying mice with sciatic nerve injury, Woolf and colleagues found that there’s a limited time window in which nerve fibers, or axons, must regenerate and extend toward the muscle, re-forming the junction known as a synapse. If this window is missed, and the muscle fibers have gone too long without stimulation, the axon is actually inhibited from going the final distance to form a synapse with them.

In mice, the window for recovering nerve function was about 5 weeks. When the nerve was simply crushed, the mice were able to stay within this window and recover motor function, because the axons grew quickly. But when the nerve was completely severed, axons were slower to begin growing, so missed the window, the team found.

The precise window for motor recovery in humans still isn’t known, but a review of data from 136 patients with carpal tunnel syndrome and 20 with cubital tunnel syndrome (a compression injury of the ulnar nerve in the elbow) showed that the shorter the period from onset of symptoms to surgery, the greater the degree of motor recovery. In the patients with cubital tunnel syndrome, muscle tests yielded an average functional score of 4 (on a scale of 0 to 5) among those who had decompression surgery within 10 months of injury, versus just 0.5 among those having surgery more than 10 months after injury, a highly statistically significant difference.”

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