MINNEAPOLIS — Louisa May Alcott is probably best known for her classic novel, "Little Women."

But it was the rash on her face in a 19th-century portrait that intrigued Dr. Ian Greaves of the University of Minnesota.

Greaves, a professor of environmental health, suspected that it held the key to a medical mystery. Now, he and a colleague think they've finally diagnosed the problem, 119 years after Alcott's death.

In a scientific paper published this spring, Greaves and Dr. Norbert Hirschhorn suggest Alcott had lupus — a chronic debilitating disease — when she wrote most of her books.

The clues, they conclude, all seem to fit, down to the distinctive rash on her cheeks and nose. If true, the diagnosis would have come as a shock to Alcott, who thought that her varied aches and pains were due to mercury poisoning; or, more poetically, that she was simply suffering for her art.

Greaves knows the pitfalls of a 21st-century physician trying to examine a 19th-century patient. But it's not the first time he and Hirschhorn, a former University of Minnesota pediatrician, have tried it.

In 2001, they reported that Abraham Lincoln might have been the unwitting victim of mercury poisoning, thanks to a pill he took for "melancholia." The pill, which was loaded with mercury, could have explained his mood swings, tremors and nerve damage, they concluded.

Not everyone bought their theory.

But ever since, Greaves and Hirschhorn have been intrigued with the idea of digging into the medical past of notable figures.

After their Lincoln report, someone suggested they look into Louisa May Alcott, who was treated with mercury after she contracted typhoid while nursing Union soldiers during the Civil War.

At the time, mercury — a dangerous toxin — was widely used for a host of ailments, Greaves said.

As a historical patient, Alcott made a tempting figure. Her journals and letters were filled with detailed accounts of her suffering: headaches, weariness, nerve pain, digestive problems.

Greaves, who knows a fair amount about mercury poisoning, studied her symptoms. And they didn't add up. She had none of the telltale signals: rage, outbursts or signs of tremor in her handwriting.

To him, it seemed more like an immune-system disorder. Then he saw the 1870 portrait that's kept at the Alcott museum, Orchard House, in Concord, Mass. There was the distinctive "butterfly-rash," a pinkish hue across Alcott's cheeks and nose, that often accompanies lupus.