The FDA has a program called the Humanitarian Device Exemption (HDE) Program which allows for medical devices intended to benefit patients in treatment or diagnosis of a disease or condition that affects fewer than 8,000 individuals per year. Since conditions like this are hard to gather enough clinical evidence to meet FDA standards, this regulatory pathway creates an alternative route where the device is exempt from the effectiveness requirements of the FD&C Act. There are some additional restrictions including certain prohibitions on profit and a cap on annual distribution number.

Source: https://www.fda.gov/medicaldevices/deviceregulationandguidance/howtomarketyourdevice/premarketsubmissions/humanitariandeviceexemption/default.htm