Endocrinology specialist diagnoses patient with rare bone-weakening disease

UC Davis

Ruth Nambooze Tucker was just 42 years old when she began experiencing pain in the joints of her ankles, knees and lower back. As a respiratory therapist, she figured her 12-hour shifts were beginning to take a toll on her body.

But a year later, Tucker’s joint discomfort was still present, and her back pain had increased significantly. She started to think something might be wrong and scheduled an appointment with her primary care doctor.

Ruth Nambooze Tucker
Ruth Nambooze Tucker was diagnosed with tumor-induced osteomalacia after struggling with joint and back pain for four years

“At my first appointment my doctor told me joint and back pain were normal as we age,” Tucker remembered. “He recommended I take Aleve, gave me stretches to do and scheduled me for physical therapy.”

Unfortunately, the physical therapy appointments made Tucker’s pain much worse. At this time, a co-worker recommended she see a chiropractor. But after 18 sessions with a chiropractor, Tucker’s conditioned remained the same.

“The chiropractor told me he had never seen a patient’s condition remain unchanged after this many appointments,” said Tucker.

After three years of powering through her discomfort and pain, Tucker began having trouble standing. When she walked, she veered to the right and had to compensate to walk straight. Tucker made another appointment with her doctor.

“During this appointment my doctor finally ordered x-rays of my back and said everything looked fine,” said Tucker. “It was at this time I started to doubt the quality of care I was receiving. I felt unheard.”

A few months later, the big toe on Tucker’s left foot began swelling. It was not painful, but it made it even more difficult for her to walk. During a virtual appointment, her doctor said he was not concerned because it was not causing her pain.

By November 2020, Tucker was in extreme discomfort. Her joint pain had spread to her shoulders, elbows and fingers. She could not cough because her ribs were so sore.

Tucker’s doctor ordered an MRI of her lower back, which revealed a pinched nerve and low lumbar fractures of her vertebrae. Despite the results, her doctor suggested rehabilitation to relieve the pain.

“That was when I decided to change my healthcare provider,” said Tucker. “Physically I had changed so much that I couldn’t even interact with my children. I was tired of not being listened to and began losing hope of ever getting better.”

Tucker switched to UC Davis Health, and visited the Pain Management Clinic.

“I still remember the appointment started at two in the afternoon and did not end until 5 p.m.,” she said. “They wanted to hear my whole story and said they aspired to find the source of what was causing my pain.”

I am so thankful to every doctor and department I interacted with at UC Davis Health. You see that they want to help you and involve you at every step of your care. When you are in pain and emotionally drained you want to be treated by someone you trust and who listens to you.” -Ruth Nambooze Tucker

The doctor ordered a full panel of bloodwork and discovered extremely low levels of phosphorus, a mineral that is essential to the formation of bones. Tucker was directed to the Division of Endocrinology, to see a specialist who focused on metabolic bone disorders.

“Seeing that Ms. Tucker had multiple fractures and low phosphorous levels, we knew there was some underlying reason why she was fracturing so easily at such a young age,” said Polly Fu Teng, assistant professor of endocrinology and orthopaedic surgery.

Teng ordered additional blood and urine tests to confirm the initial results.

“We found that her kidneys were not retaining all the phosphorous. Instead she was urinating it out, causing her blood phosphorus level to be low,” explained Teng. “Upon further testing, we found that she had a high FGF23 hormone level (fibroblast growth factor 23), which regulates phosphorus balance in our body. Once we found out that she had a high FGF23 level with her age, my main concern was that she had a tumor-induced osteomalacia.”

Tumor-induced osteomalacia is a bone-weakening disease caused by one or more typically benign, slow-growing tumors. These tumors produce high levels of FGF23, which limits the ability of the kidneys to reabsorb phosphate. The first signs of the disease, also known as oncogenic osteomalacia, include fractures, bone pain and muscle weakness.

“One of the challenges with this disorder is these patients go undiagnosed for years,” Teng said. “These tumors are classically very hard to find and fewer than 1,000 cases have been reported worldwide.”

Teng ordered a dotatate PET scan for Tucker, which is commonly used to find and monitor neuroendocrine tumors. The results showed a large mass on the big toe of Tucker’s left foot, the same toe which had swelled up the previous year.

“It was truly a relief to finally learn what was wrong with my body and to have a plan to fix it,” said Tucker.

In September 2021, over four years after her joint and back pain began, Tucker underwent surgery to have the tumor removed. Her recovery is ongoing, and her phosphorous levels are still low, but they have improved. Tucker is now pain free as she continues to take phosphorus medication and activated vitamin D to keep her levels up.

“I am so thankful to every doctor and department I interacted with at UC Davis Health,” said Tucker. “You see that they want to help you and involve you at every step of your care. When you are in pain and emotionally drained you want to be treated by someone you trust and who listens to you.”

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