By Gene Emery

BOSTON (Reuters) - Tests of a 500-year-old pinky finger confirm that Holy Roman Emperor Charles V was debilitated by gout and the painful joints it produces, Spanish researchers reported on Wednesday.

Jaume Ordi of the University of Barcelona and colleagues used a microscope to examine the tip of one of Charles' pinkie fingers, which was preserved separately from his body in a small red velvet box.

After rehydrating and slicing the mummified fingertip, the Ordi team found telltale signs of gout, including the buildup of uric acid crystals.

At the height of his 40-year reign from 1516 to 1556, Charles V controlled lands in Europe, Africa and Asia and even conquered parts of the Inca Kingdom of Peru and the Aztec Empire of Mexico.

"Despite this power, Charles V had to live within the limitations of very intense arthritic pain for most of his adult life and needed, for example, a special chair for transportation," the researchers wrote.

"His physical suffering influenced decisions that affected the future of many countries," they added.

"His physicians recommended that he follow a strict diet, but the emperor had a voracious appetite, especially for meat. He also liked to drink large quantities of beer and wine, and he even ordered a specially designed four-handled drinking mug."

The condition became so severe and distracting, it probably prompted him to put off military action against the French city of Metz, which prevented him from conquering it in 1552, according to historians. That failure, and possibly his illness, led him to abdicate to his brother, Ferdinand I, four years later.

"Charles V was only 58 years of age at his death, probably from malaria, in 1558, but he seemed an old and crippled man who could barely walk or use his hands," the researchers wrote.

Historically, gout has been regarded as a disease of the rich because the foods that increase the risk have usually only been available in quantity to the wealthy.

The concept of a Roman Empire was resurrected in the 17th century after the ancient Roman Empire had fallen centuries before.