Henry IV (Part Two, for the Shakespeareans amongst us) suffered from a particularly nasty skin disease that his contemporaries thought was leprosy. According to Peter McNiven in the English Historical Review of October 1985:
The most detailed account [of Henry's "leprosy"] is that of Thomas Gascoigne in his Loci e Libro Veritatum. On 8 June 1405, Henry had ordered the beheading of Archbishop Richard Scrope of York after the latter's unsuccessful rebellion in alliance with the earl of Northumberland. At the moment of the execution, according to Gascoigne, the king was on his way from York to Ripon when he was suddenly stricken with "horrible leprosy of the worst sort." He was compelled to break his journey seven miles from York at the village of Green Hammerson, where he was tormented by a "horrible fear" in the night which made him waken his servants with shouts of "Traitors! Traitors! You have thrown fire over me!" His attendants soothed him with strong wine and on the following day he managed to reach Ripon, where he remained incapacitated for a week. An "eye-witness" told Gascoigne that on the eighth day after Scrope's execution, he saw "great leprous pustules" projecting like teats from the king's face and hands. (pp. 747-8)
Obviously this does not describe Hanson's Disease as we know it, but "leprosy" in the Middle Ages and Renaissance was a rather vague umbrella term for skin afflictions that made people cringe and were otherwise unnamed. Henry's complaint has been variously identified as erysipelas, syphilis, and psoriasis.
He doesn't look too bad in his picture though . . . And according to Alison Weir in Lancaster and York: The Wars of the Roses, when he was exhumed in 1831 his face was well preserved and tended to indicate that the contemporary descriptions were somewhat overwrought (although he could have just gotten over the worst of the effects when he died of a stroke.)