It ranks as one of the most iconic paintings in modern American history: Andrew Wyeth's 1948 "Christina's World" depicting a woman crawling across a bleak, rural landscape with her sights focused on a distant, gray farmhouse. The portrait is imbued with an ambiguous sense of determination and hopelessness.

Wyeth's inspiration for the painting was his real-life friend and neighbor, Anna Christina Olson, a lifelong resident of the Cushing, Maine, farm on which she's pictured. Olson had a muscular disorder, long assumed to be polio, and regularly crawled across the farm, eschewing a wheelchair.

Now, after being challenged to diagnose Olson's condition, neurologist Dr. Marc Patterson of the Mayo Clinic in Rochester, Minnesota, said it was very unlikely that Olson had polio. In reviewing details of Olson's life, Patterson said the woman most likely had a form of Charcot-Marie-Tooth disease. This group of inherited disorders affects the peripheral nerves and can lead to significant problems with movement. [7 Devastating Infectious Diseases]

Patterson delivered his diagnosis today (May 6) at the Historical Clinicopathological Conference, held at the University of Maryland School of Medicine in Baltimore. The annual conference is devoted to the diagnosis of disorders that afflicted historical figures; in the past, experts have focused on the diseases of luminaries such as Vladimir Lenin, Charles Darwin and Abraham Lincoln.

Patterson said there are numerous reasons the polio diagnosis doesn't fit. First, polio is spread by a virus. If that virus invades the central nervous system, as happens in a small percentage of cases, it can cause neural damage and lead to partial paralysis, commonly in one or more limbs or in the chest. The damage comes about quite quickly, within months, but doesn't worsen after that.

However, Olson's weakness developed slowly and spread through her body over the course of her life, Patterson said. Her disease affected her feet first. At age 3, she walked on the outer edges of her soles. This implies that the muscles on one side of each foot and leg were weaker than on the other side, and this type of asymmetric symptom is not seen in polio, Patterson said. [n Images: How the Polio Vaccine Made History]

Olson could walk unassisted until she was in her 20s, although she stumbled frequently. It was around this time that her hands showed signs of muscular weakness, too, Patterson learned. In her 50s, Olson was burned while sleeping near a stove. That she could sleep through this burn implies she had difficulties with pain sensation, Patterson said.

"All of these things to me speak against polio, because polio has an acute onset, the deficit is maximum at onset, and then you get varying degrees of recovery afterwards," Patterson told Live Science.

Also, Olson was born in 1893, several years before the major polio outbreaks, further countering the polio diagnosis, Patterson said.

Adding up all the known characteristics of Olson's disease progression, Patterson speculated that the woman had Charcot-Marie-Tooth (CMT) disease. The condition was once classified as a subtype of muscular dystrophy because of the similarities of the symptoms for the two disorders. However, the progressive weakening that comes with muscular dystrophy is due to problems with the muscles themselves, whereas CMT is a disorder of the nerves that enervate those muscles.

CMT is an incurable, inherited disorder that affects approximately one in 2,500 people, according to a review published in the journal Clinical Genetics. Classic symptoms include gradual, progressive loss of muscle tissue and touch sensation across the body.

Olson's combination of motor and sensory problems makes muscular dystrophy an unlikely diagnosis, too, Patterson said.

"As a neurologist, it is always fascinating to me that there seems to be a limited number of alternatives that people think of when patients have neurologic symptoms, and I guess that's because we haven't done a good enough job at educating the public about these things," Patterson said. "Neurology is complicated."

Dr. Thomas Cole, associate editor for the Journal of the American Medical Association and an expert on art devoted to medical topics, called Patterson's diagnosis of Anna Christina Olson "an amazing piece of medical detective work."

"It brings home the fact that medicine has learned enormous amounts in the past few decades," Cole said.

Patterson was presented with Olson's case history as a clinical challenge by Dr. Philip Mackowiak, a professor emeritus at the University of Maryland School of Medicine, who organizes the Historical Clinicopathological Conference.

Olson died in 1968 at age 74. Wyeth died in 2009 at age 91. He is buried near Olson and her brother Alvaro in Maine. The change in Olson's diagnosis from polio to Charcot-Marie-Tooth disease takes nothing away of Wyeth's painting, Patterson said.

"Andrew Wyeth is really an extraordinary painter," Patterson said. "I have used [Christina's World] myself in illustrating talks in the past."

Follow Christopher Wanjek @wanjek for daily tweets on health and science with a humorous edge. Wanjek is the author of "Food at Work" and "Bad Medicine." His column, Bad Medicine, appears regularly on Live Science.