A 24-year-old woman experienced a burning sensation in her legs that worsened over two days, spreading from her toes to her thighs.

Her feet discolored, became cold, and she struggled to walk. Doctors found no pulse in the arteries supplying her lower legs and diagnosed her with a rare condition known as “holy fire” disease, or gangrenous ergotism.

Common in the Middle Ages, holy fire was caused by ingesting rye contaminated with a fungus called Claviceps purpurea. It led to burning pain, numbness, muscle spasms, and gangrene due to restricted blood flow.

In this case, the woman had taken ergotamine for migraines—normally safe—but also took ritonavir for HIV, which blocked the enzyme CYP3A4. This caused dangerous levels of ergotamine to accumulate in her blood.

After stopping ergotamine, her condition improved within two weeks. However, doctors had to amputate one toe due to gangrene-related tissue death.