The condition would have prevented the great Renaissance master from holding a palette and standing up to paint, says Vezzosi, director of the Leonardo museum in the painter's home town of Vinci. The expert says a previously unseen painting shows da Vinci with his right arm in folds of clothing that 'look like a bandage'.
The painting - showing a seated da Vinci - is attributed to a 16th-century Lombard artist. The artist's face is said to be very similar to an authenticated self-portrait, dated 1512-1517.
Vezzosi says the semi-paralysis of the right side of da Vinci's body would not have affected the left-handed artist's ability to sketch but hampered his mobility. 'It probably prevented him from standing up to paint and from holding a palette - but he would still have had enough strength to sit down and draw,' claims Vezzosi. The condition, he said, could have been caused by a stroke or by Dupuytren's disease, a disorder which leads the ring finger and little finger to stiffen.
Vezzosi said: 'The painting shows us an elderly Leonardo with all the signs of age, with his right hand suspended in a stiff, contracted position, held up by his robe as if it were a bandage.'
Da Vinci began the Mona Lisa in 1503 but never finished it. There are varying theories as to why he kept it for himself for so long - that he loved it too much or that he was not satisfied with it.
Vezzosi says the paralysis would explain da Vinci's inactivity for the last five years of his life - several of his paintings were left in an incomplete state.