The answer is "nothing"

The only common factor between these patients is Dr. Marrero. It is notable that he is not the only physician who works in that clinic, but is the only one diagnosing this condition. The most likely cause is weak diagnostic skills for challenging patients.

Unfortunately, a majority of these patients likely have Functional Neurologic Disorder https://www.mayoclinic.org/diseases-conditions/conversion-di... , which is a horrible condition that accounts for a plurality of cases seen by most neurologists. This phantom diagnosis will probably make recovery almost impossible for those people. Acceptance of that diagnosis is the number 1 positive indicator for recovery.

Source: I live in the canadian maritimes, and know many neurologists.