What is Hungry Bone Syndrome?

Hungry bone syndrome (HBS) is a rare disorder characterized by prolonged and marked hypocalcemia (low calcium), hypophosphatemia (increased levels of phosphorus), and hypomagnesemia (low magnesium).

This is a serious complication after parathyroidectomy (surgery to remove the parathyroid gland or parathyroid tumor) or thyroidectomy (surgery to remove part or all of the thyroid gland). Surgery is not the only risk factor, and if left untreated, HBS can be very serious.

This article will discuss hungry bone syndrome, its symptoms, causes, diagnosis, and treatment, and more.

Hungry Bone Syndrome Symptoms

In addition to low calcium levels, people with HBS can develop hypophosphatemia and hypomagnesemia. They may also experience muscle weakness, fatigue, and vitamin D deficiency.

Other symptoms of HBS are associated with severe hypocalcemia, including:

  • confusion or memory loss
  • muscle spasms and cramps
  • Numbness and tingling in the hands, feet, and face
  • frustrated
  • brittle and brittle nails
  • easy to fracture
  • bone pain

Symptoms of hypophosphatemia include:

  • muscle weakness
  • weak or soft bones
  • muscle wasting
  • mental state changes
  • Seizures
  • numbness
  • Rhabdomyolysis: The breakdown of muscle tissue results in the release of muscle fibers into the bloodstream, which are bad for the kidneys

If left untreated, severe hypophosphatemia can lead to coma or death.

Symptoms of hypomagnesemia include:

  • Nystagmus (abnormal eye movement)
  • tics (uncontrollable muscle contractions)
  • fatigue
  • muscle cramps or spasms
  • muscle weakness
  • numbness


About 13 percent of people who have parathyroidectomy for primary hyperparathyroidism (overactive parathyroid glands) develop HBS. Although doctors consider it a complication of thyroid surgery, research on this condition is very limited.

It is common for hyperparathyroidism to have a drop in blood calcium levels after parathyroidectomy, but this usually goes away within a few days. Serum calcium levels that fall severely over four days become HBS.

READ ALSO:  when you don't have a thyroid

HBS has been reported in 25%–90% of people with radiographic (X-ray) evidence of hyperparathyroidism bone disease (also called osteitis fibrosa) and up to 6% of people without bone involvement .

Hyperparathyroidism occurs when one of the parathyroid glands is overactive (hyperparathyroidism) and there is too much parathyroid hormone (PTH), which causes the bones to release too much calcium into the blood. This causes bones to lose density and stiffness.

Various risk factors are thought to contribute to the development of HBS. These may include:

  • older
  • Weight and volume of excised parathyroid glands
  • Radiographic evidence of bone disease caused by osteitis fibrosus
  • vitamin D deficiency
  • primary hyperparathyroidism
  • Secondary hyperparathyroidism: This type of hyperparathyroidism occurs when another condition causes calcium levels in the body to decrease, and over time, PTH levels increase.
  • Thyrotoxicosis: This is an excess of thyroid hormones in the body. People with this disorder also have lower levels of thyroid-stimulating hormone (TSH) in their blood.
  • Osteoblastic Bone Metastasis: Hungry bone syndrome is also associated with the spread of this type of cancer to the bone. It is sometimes seen in lung, kidney, breast and prostate cancer. In these cases, it is the result of excessive new bone formation.
  • Parathyroid cancer: This is an extremely rare but aggressive and life-threatening form of hyperparathyroidism.


HBS is often undiagnosed after parathyroidectomy in patients with primary or secondary hyperparathyroidism. You should contact your doctor if you develop symptoms of hypocalcemia, especially after parathyroid or thyroid surgery.

READ ALSO:  Overview of Hypoparathyroidism

People with HBS experience signs and symptoms of hypocalcemia. Physical examination may reveal fractures (fractures), skeletal deformities, recent surgical scars from parathyroid or thyroid removal, and persistent muscle fiber activity with spasticity and muscle relaxation.

Your doctor will check your blood calcium levels. Severe and persistent low calcium levels (less than 8.4 milligrams per deciliter (mg/dL)) and hypophosphatemia for more than 4 days after surgery are usually sufficient to diagnose HBS.

Low calcium levels are thought to follow a sudden drop in high PTH levels. This causes calcium to flow into “calcium-deficient” bones.

HBS is frequently reported after parathyroidectomy or thyroidectomy due to primary or secondary hyperparathyroidism. The longer PTH levels remained elevated, the greater the severity of post-operative hypocalcemia.


If left untreated, HBS can lead to complications related to hypocalcemia. Complications may include seizures, arrhythmias (irregular heartbeats), severe muscle spasms and spasms, and impaired brain and motor function.

The main goal of HBS treatment is calcium supplementation. This is usually done with calcium supplementation and high doses of vitamin D and electrolytes.

Recommended HBS treatment begins with 6 to 12 grams of elemental calcium per day. Calcium is given intravenously (IV, intravenous) and then switched to oral supplements.

Treat hypomagnesemia as needed. Doctors often delay treatment for low magnesium levels because supplemental magnesium may slow the effects of calcium replacement.

For similar reasons, treatment of hypophosphatemia is often delayed until calcium levels improve. Once calcium levels are up, both magnesium and phosphorus levels can be restored.

READ ALSO:  Protecting Your Family After Radioactive Iodine Treatment

Studies have shown that correcting vitamin D levels can significantly reduce the effects of HBS. Vitamin D deficiency is often associated with hungry bone syndrome and hyperparathyroidism, and restoring vitamin D to normal levels helps balance calcium.


For most people with HBS, the prognosis is likely to be good. However, there are some differences in the time it takes for the condition to improve. In some cases, calcium and vitamin D replacements are required for up to a year after surgery.

For some people, starving bone syndrome may last up to nine months before calcium levels return to normal. It may take longer if HBS is caused by parathyroid cancer.


Hungry bone syndrome is a rare disorder that causes significant long-term reductions in calcium levels. It may also lead to higher phosphorus levels and lower magnesium levels. Risk factors for this condition are parathyroidectomy and thyroidectomy.

HBS is usually treated by restoring calcium levels and balancing vitamin D. The prognosis for most HBS patients is good, especially when calcium levels are supplemented.

VigorTip words

If you have had a parathyroidectomy or thyroidectomy, you may have postoperative hypocalcemia or hungry bone syndrome. Your medical team will work diligently to monitor your calcium, parathyroid hormone, phosphorus, and magnesium levels after surgery.

If you have other risk factors, such as hyperparathyroidism bone disease, you should discuss your risk for HBS with your doctor. This is the best way to deal with severe low calcium problems and complications.