Plagueheart Leggings

Plagueheart Leggings are leg armor for warlocks. They are part of the Plagueheart Raiment armor set.

Source
The leggings are a quest reward from Plagueheart Leggings (quest), crafted by a vendor from the Desecrated Leggings, an item which drops from Loatheb who currently resides in Naxxramas.