Hungry Bone Syndrome

What is hungry bone syndrome?

Hungry bone syndrome (HBS) happens when you have very low calcium levels in your blood (hypocalcemia) as a result of parathyroid surgery.

People with HBS often also have hypomagnesemia and hypophosphatemia. Hungry bone syndrome is treatable.

How common is hungry bone syndrome?

Researchers aren’t sure how often hungry bone syndrome happens. Some studies show that it develops in 4% to 13% of people who’ve had a parathyroidectomy for primary hyperparathyroidism. After parathyroidectomy for secondary and tertiary hyperparathyroidism, it develops in 20% to 70% of cases.

What are the symptoms of hungry bone syndrome?

The symptoms of hungry bone syndrome are similar to those of hypocalcemia. They can range from mild cramping to confusion and seizures. Symptoms can include:

• Muscle cramps or spasms.
• Muscle weakness.
• Bone pain.
• Fatigue.
• Confusion.
• Memory problems.
• Irritability or restlessness.
• Depression.
• Tingling in your lips, tongue, fingers and/or feet.
• Muscle spasms in your throat that make it difficult to breathe (laryngospasm).
• Stiffening and spasms of your muscles (tetany).
• Seizures.

People with HBS may also have hypomagnesemia and hypophosphatemia. The symptoms of these conditions are similar to hypocalcemia. They can also cause muscle issues, seizures and arrhythmia.

Hungry bone syndrome typically develops within 18 hours of parathyroid or thyroid surgery.

What causes hungry bone syndrome?

Hungry bone syndrome can occur:

• After parathyroidectomy for primary or secondary hyperparathyroidism.
• After total thyroidectomy for thyrotoxicosis.
• With prostate cancer that’s metastasized (spread) to your bones.

To understand why hungry bone syndrome happens, it helps to understand how your body manages blood calcium levels.

Parathyroid hormone (PTH) is a hormone that your parathyroid glands release to control the level of calcium in your blood (not your bones). PTH also helps control the levels of phosphorus (a mineral) and vitamin D (a hormone) in your blood and bones.

Your parathyroid gland releases PTH when your body detects low calcium levels in your blood. PTH stimulates the release of small amounts of calcium from your bones into your bloodstream.

After parathyroid surgery for overactive parathyroid, your PTH levels drop suddenly (after previously being high). Thyroid surgery can also cause low PTH levels because the surgeon can accidentally damage your parathyroid glands in the process. (Your parathyroid glands exist behind your thyroid.)

The sudden drop in PTH levels leads to decreased resorption (remodeling) of old bone calcium and increased bone formation. This makes your bones “hungry” for calcium, hence the name, “hungry bone syndrome.”

HBS can also happen in metastatic prostate cancer that’s spread to your bones. It happens because increased osteoblastic activity (bone-building) leads to an increased need for bone calcium.

What are the risk factors for hungry bone syndrome?

Risk factors for HBS include:

• Elevated parathyroid hormone levels.
• Elevated alkaline phosphatase levels.
• Lower blood calcium levels.
• Vitamin D deficiency.
• Simultaneous thyroid and parathyroid surgery.
• Elevated blood urea nitrogen (BUN) levels.
• Obesity.
• Removal of a larger-than-average volume of overactive parathyroid glands.
• Metastatic tumors of the bones.
• The presence of bone diseases, such as brown tumors and osteitis fibrosa cystica.

How is hungry bone syndrome diagnosed?

Healthcare providers use a calcium blood test to diagnose hungry bone syndrome. Most providers consider a blood calcium level of less than 8.4 mg/dL for more than four days to be a risk factor for HBS.

Your provider may also perform the following tests to check if HBS has affected other aspects of your health:

• Other blood tests: Your provider may do more blood tests to check your levels of magnesium, phosphorus, parathyroid hormone (PTH) and/or vitamin D.
• EKG (electrocardiogram): An EKG is a procedure that uses electrodes attached to your chest to measure your heart rhythm. Hypocalcemia and HBS can cause an abnormal heart rhythm.
• Bone imaging tests: Bone imaging tests can check to see if you have bone issues, such as fractures, deformities or tumors.

How do you treat hungry bone syndrome?

The main goal of treatment for hungry bone syndrome is to return to healthy blood calcium levels. You’ll likely receive treatment in a hospital. Treatment includes:

• IV calcium (calcium gluconate).
• Oral calcium supplements (calcium citrate or calcium carbonate).
• Oral vitamin D supplements.
• Magnesium replacement.

Can hungry bone syndrome be prevented?

As HBS can happen after parathyroidectomy or thyroidectomy, healthcare providers take steps to try to prevent it, including:

• Presurgery evaluation: Before the surgery, your provider will check your bone mineral density, blood calcium levels, phosphate levels, PTH levels and vitamin D levels. These tests can help your providers know if you’re at risk of developing HBS.
• Preventive measures: If you’re at high risk of developing HBS, your provider may recommend taking supplements or medication before surgery to make sure your vitamin D and calcium levels are where they should be. This may help reduce your likelihood of developing HBS and/or its severity.
• Post-surgery monitoring: Your healthcare team will closely monitor your levels of calcium, phosphate, magnesium and PTH after surgery. This can allow them to quickly catch HBS if it develops and start treatment right away.

Despite all these measures, it’s still possible to develop HBS. Researchers aren’t sure why this happens.

What is the prognosis for hungry bone syndrome?

The prognosis (outlook) for hungry bone syndrome is excellent. However, even with treatment, the length of time HBS lasts ranges from days to months. Some cases last up to a year.

If left untreated, severe hypocalcemia can cause life-threatening complications such as seizures.

When should I see my healthcare provider?

If you experience symptoms of hypocalcemia, like muscle cramps or spasms and mental changes, see your healthcare provider as soon as possible. Hungry bone syndrome and hypocalcemia can come and go after parathyroid and/or thyroid surgery.

A note from Cleveland Clinic

Hungry bone syndrome can happen after you have parathyroid or thyroid removal surgery. The good news is that it’s treatable. However, it may take time for it to go away. Severe hypocalcemia can be dangerous to your health, so it’s important to see your healthcare provider as soon as you experience symptoms.