'Teen Mom 2': Leah Messer Gets Surprising News About Ali's Diagnosis in Exclusive Sneak Peek

Leah Messer is in for a surprise when it comes to the latest update on daughter Aliannah's health. The 11-year-old was diagnosed six years ago with Titin Myopathy Muscular Dystrophy, a rare form of the progressive disease, and both Messer and Ali's father, Corey Simms, didn't expect to get such a positive update from her neuromuscular specialist, Dr. Tsao, during a recent telehealth appointment.

In a PopCulture exclusive sneak peek of Tuesday's episode of the MTV show, Leah gets her daughter excited to meet with her doctor and tell him just how well her new power wheelchair is working. "Ali's been in and out of doctor's visits her whole life," Leah tells the camera. "But we finally got a diagnosis six years ago. Since then, Dr. Tsao has been monitoring her progress."

Conferencing in Simms, Tsao seems happy that Ali now can use her power wheelchair to "conserve energy," which will be "very good for her" and prevent her disease from progressing as quickly as if she were to exhaust her muscles moving around too much. Tsao then advises Messer and Simms that while there were fewer than 20 Titin Myopathy Muscular Dystrophy cases documented worldwide when Ali first was diagnosed, that pool has been expanded to several hundred people.

"And they've found that many patients like Aliannah's situation — with no heart or lung involvement — can live into their 70s at least," Tsao tells the trio. Messer is clearly excited at the news but admits the topic of life expectancy isn't one she and Simms have brought up extensively when helping Ali understand her diagnosis. "I think Ali understands her disease a lot better than she used to, and Ali's life expectancy is something I don't want her to ever worry about," Messer shares with the camera. "But deep down it was something that was a weight for me and her dad."

"We didn't know how progressive the disease would be and how quickly it would happen, but with discovering more cases, it gives me hope for my little girl," she says, emotion evident in her voice. "I feel like we can look further into her future — it does bring us hope." Teen Mom 2 airs Tuesdays at 8 p.m. ET on MTV. Catch up on previous episodes on Paramount+, which can be subscribed to with a free trial here. Disclosure: PopCulture is owned by ViacomCBS Streaming, a division of ViacomCBS.