Abby Lee Miller's Doctor on the 'Serious' Condition That 'Almost Undid' Her Gastric Sleeve Surgery (Exclusive)

The former 'Dance Moms' star was hospitalized on Tuesday.

Abby Lee Miller's doctor is opening up about her recent hospitalization. 

Weight loss surgeon Dr. Michael Russo, who performed the Dance Moms star's gastric sleeve surgery last year, exclusively tells ET about the underlying cause of her pain, and why her condition has become so serious. Miller consented for Dr. Russo to share her current medical condition with ET after their meeting on Wednesday. 

According to Dr. Russo, Miller's current situation "is not a good one," after a source told ET that Miller was taken to the hospital on Tuesday for a lingering back injury. 

Russo tells ET that Miller's pain stems from severe hypothyroidism, which occurred after she stopped taking one of her thyroid medications. 

"Her hypothyroidism got so severe she had an assortment of symptoms. Most dramatic is severe muscle and bone pain in her back, shoulders, arms and legs," Dr. Russo reveals. "When Abby first went to the ER, she was almost unable to move [her] arms and legs and was having trouble getting out of bed. She had numbing and tingling in her hands and feet. She couldn't even hold a spoon in her hand."

"Hypothyroidism can give you severe muscle cramping, weakness and pain. You can have severe difficulty moving your arms and legs. If left untreated it's been reported people can become comatose," he explains. "This is a serious medical concern." 

Dr. Russo says that Miller was "instructed to stop" taking her thyroid medication by another doctor at the end of January, but that hypothyroidism has led her to the emergency room twice. 

"The good news is we got it addressed quickly. She's already feeling better because we are supplementing her medications back in and she is on the road to recovery, but a lot of damage was done," he notes. "An additional consequence of being off the medication is that hypothyroidism can cause weight gain. This almost undid part of her gastric sleeve surgery and caused her to gain a bit of weight back. But she is back on track and getting back to where she was in January." 

ET learned that Miller returned to her halfway house on Tuesday night, where she's been serving the remainder of her prison sentence. The reality star star was released from the Federal Correctional Complex in Victorville, California, last month, after spending eight and a half months behind bars for bankruptcy fraud, and is scheduled to be released from the halfway house on May 25.

Now, Dr. Russo says his primary focus is to get Miller "back to where she was at the end of January, when she was down a whole bunch of weight and excited to get back to her life." He says Miller had lost almost 100 pounds since undergoing gastric sleeve surgery last year, and after meeting with him on Wednesday, she's in "better spirits." 

"She's in a much better place," he shares. "This is a regaining of her life." 

See more on Miller in the video below. 

Reporting by Rande Iaboni.