. >> reporter: sally massagee had all but given up. take a look at her back. it was as if muscle mass was consuming her body. sally was transforming into the incredible hulk. so this is sally's mri of the brain. that's incredible. >> even the muscles that govern the movements of the eye, which are really small muscles, are huge. the knew row radiologist saw this and sort of went wild over this. look at the size of those. they're three to four times bigger. >> they probably really had never seen anything quite like this. >> right. because there's no way to make those muscles big by moving your eyes a lot. it's not like lifting weights, so why would they be that big? >> reporter: it was a mystery. no doctors, no specialists, no one could diagnose what was happening to sally. which is why she was selected to come here. it's called the udp. the undiagnosed diseases program. it's a medical mystery ward. kylie mcpeak is 6. she was also selected to come to the udp. >> she knows she's different, but it doesn't seem to faze her. she kind of seems like she's just like a

time was running out. >> reporter: at 53 years old, sally massagee was physically ripped. >> everybodyssumed that i spent a whole lot of time in the gym. >> reporter: but sally didn't lift weights. whatever was causing her body to bulk up uncontrollably was taking away her ability to live her life. >> it was very frustrating. i was losing the ability to do the things i loved to do. it became increasingly difficult just to walk. at some point i knew if it continued it would kill me. >> reporter: she'd seen countless medical specialists. inform one had an explanation. and that's why dr. william gall and his team of world class specialists at the undiagnosed diseases program was trying to solve the mystery. >> this is super impressive. i mean, you literally see a cleavage right in the middle of her back because those muscles are so big. dr. william gall, the program investigator. >> bottom line, it's not acromegaly, just confined to the muscle, what in the world could this be? >> at the undiagnosed diseases program, sally went through a gruelling week of exams and tests, including a muscl

. >>> tonight we continue our doctor detectives series with a remarkable update on sally massagee. u may remember we introduced you to sally last week. sanjay gupta followed her story for more than a year. she searched for years for a diagnosis but no one could tell her why her muscles were growing out of control. sanjay met her at the national institutes of health. time was running out. >> reporter: at 53 years old, sally massagee was physically ripped. >> everybody assumed that i spent a whole lot of time in the gym. >> reporter: but sally didn't lift weights. whatever was causing her body to bulk up uncontrollably was taking away her ability to live her life. >> it was very frustrating. i was losing the ability to do the things i loved to do. it became increasingly difficult just to walk. at some point i knew if it continued it would kill me. >> reporter: she'd seen countless medical specialists. inform one had an explanation. and that's why dr. william gall and his team of world class specialists at the undiagnosed diseases program was trying to solve the mystery. >> this is sup