Ancient Eygptians had arthritis.
Seriously! Think about it. Look at any ancient Eygptian picture of people: They're very stiff looking. Even their statues were very stiff and rigid. They loved the heat, Wore linen pyjamas all day, and knew more about medicine than many cultures at the time, using myrtle leaves as a basic form of aspirin and lime stone as antacid.
Need more proof? We even have a dance move like how they're pictured: The poor things! We've been picking on them this whole time not even realising it.
Well, maybe not all of them had it, but someone had to. :)