Delivering a One-Two Punch for Peripheral Neuropathies

During neurologist Michael Polydefkis’ fellowship at Johns Hopkins in the late 1990s—a natural next step after medical school and residency here—he was working in the lab one day with Justin McArthur and Jack Griffin examining punch skin biopsy samples. The two senior physician-scientists, who eventually rose to current and former chair of Johns Hopkins’ Department of Neurology, had developed the punch skin biopsy technique several years earlier as a way to spot problems in the small caliber nerves that sense touch, pain, and temperature. Absentmindedly, Griffin commented that one day neurologists would carry a reflex hammer for testing reflexes, a tuning fork to test sensation, and a skin punch tool for taking the small, circular samples of skin necessary for their technique.
“That really got me thinking and set me on my course,” Polydefkis
Their biopsy technique offered the first definitive and minimally invasive diagnosis for peripheral neuropathies, damage to nerve cells outside the brain and spinal cord caused by diseases, such as diabetes or HIV, or as a side effect from treatments including cancer chemotherapies. Rather than removing a large nerve from the leg to look for this damage as doctors had done in the past, which involved
significant surgery and often left patients with pain or numbness, punch skin biopsies remove just a tiny piece of skin just millimeters in diameter. Looking under the microscope, any damage to the skin’s small caliber nerves is easily visible, sparing patients the need for larger surgery.
“These nerve fibers in the skin are among the first markers of peripheral neuropathies, the canaries in the coal mines that we use to diagnose patients early,” Polydefkis explains.
But what began as just a diagnostic technique has morphed into much
more. After taking on more and more responsibility at Johns Hopkins’ Cutaneous Nerve Laboratory over the years and becoming its director in 2004, Polydefkis, has led a team of physician-scientists, laboratory coordinators, technicians and students that have expanded the uses for punch skin biopsies and published numerous research papers involving this technique. Now, these biopsies can track nerve
damage from chemotherapies over time, allowing researchers to study how these drugs affect the nervous system during the course of treatment. They can also be used to track nerve regrowth after damage in both humans and animal models such as mice, allowing researchers to determine which factors might slow healing and test whether drugs or other interventions might help speed it up.
“Taking a small piece of skin is pretty innocuous and has helped fill a tremendous void for diagnosis and research,” says Polydefkis, who also sees patients with peripheral neuropathies and other nerve damage in the clinic.
His energies into helping those with disabilities extend beyond the clinic and lab. After sustaining a serious spinal cord injury when he was 12 years old, he has become a role model for students and trainees with disabilities. Polydefkis has an important role as a member of the Johns Hopkins University Diversity Leadership Council, aiding others with disabilities to be as productive as possible during their time at the university.
“He’s been an incredible role model,” says current Department of Neurology director McArthur, “for others in our field and beyond.”