While PGS is extremely rare, it can cause lingering pain, amputations, even death. PGS was first reported in 1980, when patients receiving the drug by IV noticed their hands swelling, becoming painful and turning a deep shade of violet. The FDA notes that only 43 cases have been documented and that it is very likely under-reported.
The precise cause of PGS is not known, but it is known to result from a toxic drug being injected directly into a vein that also seeps into underlying tissue. The damage is frequently permanent. According to report on msnbc.com, studies suggest that severe cases of PGS occur in six percent of patients who receive IV phenytoin, with less serious adverse events seen in as many as 25 percent of patients.