Famed artist and inventor Leonardo da Vinci suffered from a crippled right hand late in life, usually attributed to a stroke. In a new paper in the Journal of the Royal Society of Medicine, two Italian researchers argue that Leonardo more likely suffered from a condition colloquially known as "claw hand." They base their argument on analysis of a 16th-century portrait of an elderly Leonardo.

The quintessential Renaissance man was the illegitimate son of a Florentine notary named Piero Fruosino di Antonio da Vinci. (His mother, Caterina, was a peasant.) Much of what we know about Leonardo's life comes from the writing of the 16th-century painter and historian Giorgio Vasari, in Lives of the Most Excellent Painters, Sculptors, and Architects.

Historians have also studied Leonardo's drawings and his use of "mirror writing" in his journals, concluding he was almost certainly predominantly left-handed, although he was ambidextrous to some extent. For instance, he wrote and drew with his left hand but never painted with it. Vasari noted that Leonardo in his prime "was physically so strong that... with his right hand he could bend the ring of an iron door knocker or a horseshoe as if they were lead."

“One cannot indeed expect any more good work from him, as a certain paralysis has crippled his right hand.”

But when Antonio de Beatis, personal assistant to Cardinal Luigi d'Aragona, visited Leonardo's workshop in 1517, he noted in his diary, "One cannot indeed expect any more good work from him, as a certain paralysis has crippled his right hand." This would explain why Leonardo produced far fewer paintings in his last years, although he continued to teach and make many sketches and drawings. His right hand had been damaged, and he could no longer use it to hold palettes and brushes, although he could still write and draw with his dominant left hand.

There was strong consensus among historians that Leonardo likely suffered a stroke (possibly due to a vegetarian diet high in dairy) in his final years that left his right hand gnarled and unusable. Alternatively, he may have suffered from Dupuytren's disease, a rare condition that severely contracts and cripples the hand.

The Italian researchers, Davide Lazzeri and Carlo Rossi, argue that both these diagnoses are wrong. Instead, they advocate that a fainting episode damaged the ulnar nerve in his right hand, leading to ulnar palsy (aka claw hand) and making fine motor movement nearly impossible.

As evidence, they point to a portrait of the elderly Leonardo attributed to Giovanni Ambrogio Figino. (The red-chalk portrait is in the so-called sanguine technique because it has the same reddish-brown color as dried blood.) It shows the polymath's right arm resting in folds of clothing, stiffly suspended in a contracted position. If that stiffness were due to a stroke, the hand would most likely be gnarled and clenched. Also, no account describes Leonardo suffering any other common ill effects of stroke, such as cognitive impairment or facial paralysis. The researchers rule out Dupuytren's disease because it comes on slowly, and a 1505 portrait by Marcantonio Raimondi shows Leonardo in his 50s playing a stringed instrument similar to a fiddle with a fully functioning right hand.

"Rather than depicting the typical clenched hand seen in post-stroke muscular spasticity, the picture suggests an alternative diagnosis such as ulnar palsy, commonly known as claw hand," said Lazzeri, a specialist in plastic reconstructive and aesthetic surgery at the Villa Salaria Clinic in Rome. "This may explain why he left numerous paintings incomplete, including the Mona Lisa, during the last five years of his career as a painter while he continued teaching and drawing."

DOI: Journal of the Royal Society of Medicine, 2019. 10.1177/0141076819848115 (About DOIs).