'KUWTK': Kim Kardashian’s Mystery Illness Finally Revealed Following Lupus Scare

The reality star found out the true cause behind the severe pain in her joints.

Last week's Keeping Up With the Kardashians left fans wondering if Kim Kardashian-West did, in fact, have lupus after the reality star tested positive for lupus antibodies.

On Sunday, Kim went in for an ultrasound on her hands -- where she's been experiencing pain the worst -- to see if having lupus antibodies meant she was actually afflicted with the ailment.

Fortunately, the doctor deemed that Kim was not battling lupus. However, her joint pain is very real, and not a result of the carpal tunnel she was diagnosed with last year. Instead, it turns out she's got psoriatic arthritis, resulting from her psoriasis.

"First of all, if you have any evidence for lupus, we would have screened it," Kim's doctor explained in the episode. "You do not have lupus and rheumatoid arthritis. So, you can be reassured. You probably have psoriatic arthritis because psoriasis comes and goes. There’s nothing there right now."

Kim went on to explain that she felt "so relieved" to know that her health issues were not nearly as severe as they could have been.

"The pain is going to come and go sometimes, but I can manage it," Kim explained. "This isn’t going to stop me."

ET spoke with Kim last week, where she revealed that she's "on a medication now, so everything seems to be fine for right now," and she's "just rolling with it day by day."

However, when she first found out she potentially could have lupus, the mother of four admitted she felt scared and depressed at what that would mean for her family.

"When you do have a diagnosis -- or you get tested for something and you get a result that you weren't expecting -- you definitely get in your head and for a second you kinda get this little depression of, like, 'OK, what are all of the possibilities that can happen? What's my life gonna look like? I really wanna be active for my kids.' And so it triggers something," Kardashian shared.

"I really had to get myself together because I do have kids and I do have a family that I just have to be positive and get it together for," she continued. "No matter what's going on in your life, you can take that time to grieve for a second… and then figure out how to be positive about it because it's not going to change. There's no point in being depressed and staying in that head space, but I felt it for a minute."

Check out the video below to hear more.

Keeping Up With the Kardashians airs Sundays at 9 p.m. ET/PT on E!