The Arm-Brain Connection

Dancer inspires insight into new ways of approaching brachial plexus

Sydney Sanborn was a 9-pound baby whose shoulder was pinched in the birth canal, leaving her with brachial plexus palsy. The injury damaged her left arm so severely that her mother used to safety pin her sleeve to her chest so her limb wouldn’t get in the way.

As a toddler, Sydney received physical therapy but grew up favoring her right side. By the time she was in fifth grade, she couldn’t put her hair in a ponytail or touch the back of her neck with her left hand because of limited recovery of her shoulder movement.

Her pediatrician in Columbus referred her to the Brachial Plexus Center at Cincinnati Children’s, where orthopaedic surgeon Charles Mehlman, DO, MPH, operated to partially release her subscapularis tendon and muscle to allow her shoulder to rotate.

Sydney’s rehabilitation physician, Linda Michaud, MD, was delighted that Sydney could finally move her left arm without pain, fix her own hair and do things she couldn’t do before.

Doctors thought they had “fixed” her injury, as her ability to move, especially at the shoulder, was significantly improved.

But something Sydney said made them want to investigate further. She said when she danced, she would sometimes “forget to use” her left arm.

Mehlman and Michaud, co-directors of the Brachial Plexus Center, wondered why Sydney’s recovery of function seemed incomplete.

They hypothesized that, even though Sydney’s brachial plexus injury was a peripheral nerve injury and her shoulder had been repaired, perhaps communication between her arm and her brain was not the same on both sides.

They sought the help of Donald Gilbert, MD, MS, director of the Movement Disorder Clinic and a pediatric neurologist at Cincinnati Children’s.

Gilbert used transcranial magnetic stimulation (TMS) to measure how Sydney’s left arm was communicating with her brain.

For more than 100 years, doctors have thought of brachial plexus injuries as peripheral nerve injuries and not appreciated effects at the level of the brain, Michaud says.

But Gilbert’s findings left Michaud rethinking the contribution of cortical (brain) representation of the arm. TMS found that the electrical pathways between Sydney’s arm and brain were not the same on both sides.

“What we found in this girl who forgets to use her arm when she dances,” Gilbert says, “is that the side of the brain that controls the arm with the brachial plexus injury resembles the side of the brain of somebody who can’t use her arm because of a stroke.”

It took much more energy during TMS to get a normal response in Sydney’s once-damaged side, Gilbert says.

“If the same holds true for lots of kids with brachial plexus injuries, then repairing the peripheral nerve or muscle isn’t enough,” Gilbert says. “If you really want to normalize motor outcomes, we need to make sure that they wire their brains in early childhood to use both hands normally.