Understanding Secondary Hyperparathyroidism

To understand secondary hyperparathyroidism, it helps to know what the parathyroid glands normally do. You have four tiny parathyroid glands in your neck, each about the size of a grain of rice, located behind the thyroid gland. These small but important glands produce parathyroid hormone, or PTH, which helps your body maintain the right levels of calcium and phosphorus in the blood^[1].

In secondary hyperparathyroidism, something outside the parathyroid glands themselves goes wrong. This outside problem causes calcium levels in the blood to drop too low or phosphorus levels to rise too high. In response, the parathyroid glands work harder and harder, making more PTH to try to correct the imbalance. Over time, this constant stimulation causes all four parathyroid glands to grow larger and become overactive^[2].

This condition is different from primary hyperparathyroidism, where a growth or tumor on one parathyroid gland causes it to produce too much hormone on its own. In secondary hyperparathyroidism, the glands are simply responding to signals from the body that something else is not working properly^[3].

Epidemiology: Who Gets Secondary Hyperparathyroidism?

The most common causes of secondary hyperparathyroidism are vitamin D deficiency and chronic kidney disease. About half the world’s population is affected by vitamin D insufficiency, which creates an enormous pool of people potentially at risk^[4].

Chronic kidney disease affects approximately 15% of the population in the United States. Among people with kidney disease, the risk of developing secondary hyperparathyroidism increases dramatically as kidney function declines. There is a strong relationship between how advanced the kidney disease is and how likely someone is to develop elevated PTH levels. As people move through the stages of chronic kidney disease, from early stages to more advanced ones, the prevalence of secondary hyperparathyroidism rises^[4].

People on dialysis are especially likely to experience this condition. Despite improvements in medical treatments, secondary hyperparathyroidism remains a significant challenge for people with kidney failure. The condition can lead to serious complications affecting the heart, blood vessels, and bones, contributing to illness and early death in this population^[4].

Causes: What Triggers This Condition?

Secondary hyperparathyroidism develops when another health problem interferes with the body’s ability to maintain normal calcium and phosphorus balance. The parathyroid glands themselves are healthy, but they receive signals that calcium is too low or phosphorus is too high, prompting them to release more PTH^[5].

The most common cause is chronic kidney disease. When the kidneys fail, they can no longer convert vitamin D into its active form, called 1,25-cholecalciferol. Without enough active vitamin D, the intestines cannot absorb calcium properly from food, leading to low blood calcium levels. At the same time, failing kidneys cannot remove phosphorus effectively, so phosphorus builds up in the blood. Both of these problems send strong signals to the parathyroid glands to make more PTH^[4].

Vitamin D deficiency is another major cause. Even in people with healthy kidneys, not having enough vitamin D means the body cannot absorb calcium from the digestive system efficiently. This leads to low calcium levels, which trigger the parathyroid glands to compensate by releasing more hormone^[5].

Less commonly, secondary hyperparathyroidism can result from conditions affecting the digestive system. Diseases that cause malabsorption, such as chronic pancreatitis or small bowel disease, prevent the body from absorbing fat-soluble vitamins like vitamin D. Some types of weight-loss surgery that alter how the intestines work can also lead to vitamin D deficiency and calcium malabsorption. Additionally, conditions where the body loses too much fat in the stool, called steatorrhea, can interfere with vitamin D absorption^[7].

Risk Factors: Who Is More Vulnerable?

People with chronic kidney disease, especially those in advanced stages or on dialysis, face the highest risk of developing secondary hyperparathyroidism. As kidney function declines through the stages of kidney disease, the risk increases substantially^[4].

Anyone with low vitamin D levels is at increased risk. This can include people who do not get enough sunlight exposure, those with dark skin (which produces less vitamin D from sunlight), older adults whose skin becomes less efficient at making vitamin D, and people who do not consume enough vitamin D in their diet^[4].

People who have undergone certain gastrointestinal surgeries, particularly weight-loss procedures that alter the intestines, are at higher risk because their bodies may have difficulty absorbing vitamin D and calcium. Those with digestive diseases affecting the small intestine, where most nutrient absorption occurs, also face elevated risk^[7].

Not getting enough calcium in the diet can contribute to the condition as well, though this is less common in developed countries where dairy products and fortified foods are widely available^[7].

Symptoms: What Does It Feel Like?

Many people with secondary hyperparathyroidism do not notice any symptoms in the early stages. The condition is often discovered during routine blood tests ordered for other reasons^[6].

When symptoms do appear, bone and joint pain are among the most common complaints. The bones can become weak and painful because PTH signals them to release calcium into the bloodstream continuously. Over time, this makes bones thin and brittle. Some people develop visible limb deformities as the bones weaken^[7].

Muscle weakness and fatigue are frequent symptoms that can affect daily activities. People may feel tired all the time and find it difficult to perform tasks that previously seemed easy. Some experience trouble concentrating or problems with memory^[6].

Emotional symptoms can include depression and mood changes. Loss of appetite is common, along with nausea and vomiting. Constipation may develop. Some people experience increased thirst and find themselves needing to urinate more frequently^[6].

In people with kidney failure and severe secondary hyperparathyroidism, PTH levels can climb into the hundreds or even thousands. Some may develop severe, uncontrollable itching called pruritus. A serious complication called calciphylaxis can occur, where calcium deposits form in the skin and muscles. This causes extremely painful skin lesions that can lead to tissue death and open ulcers^[5].

Prevention: Can It Be Avoided?

Preventing secondary hyperparathyroidism focuses on addressing the underlying causes before the parathyroid glands become overactive. For people with chronic kidney disease, working closely with healthcare providers to slow the progression of kidney disease is important. This includes managing blood pressure, controlling blood sugar if diabetic, and following dietary recommendations^[4].

Maintaining adequate vitamin D levels is crucial. Getting enough sunlight exposure, when possible and appropriate for your skin type, helps the body produce vitamin D naturally. Eating foods rich in vitamin D, such as fatty fish, fortified milk and dairy products, and fortified cereals, supports healthy levels. For people who cannot get enough vitamin D from sun and food, supplements may be necessary^[4].

Ensuring sufficient calcium intake through diet is also important. Dairy products, leafy green vegetables, and fortified foods provide calcium. However, people with kidney disease need to be careful not to consume too much calcium without medical guidance, as this can cause other problems^[7].

Regular monitoring of calcium, phosphorus, and PTH levels through blood tests allows healthcare providers to detect problems early, before the parathyroid glands become significantly enlarged. Early intervention with dietary changes, vitamin D supplementation, or phosphate binders can help prevent the condition from progressing^[4].

Pathophysiology: How the Body Changes

Understanding what happens inside the body during secondary hyperparathyroidism helps explain why symptoms develop and why treatment is necessary. The process begins with either low calcium levels, high phosphorus levels, or insufficient active vitamin D. These changes trigger the parathyroid glands to release more PTH^[4].

In a healthy person, PTH acts on three main targets: the bones, the kidneys, and indirectly on the intestines. PTH signals bone cells called osteoclasts to break down bone tissue, releasing calcium and phosphorus into the bloodstream. In the kidneys, PTH tells the cells to hold onto calcium and pass it back into the blood instead of losing it in urine. At the same time, PTH instructs the kidneys to get rid of more phosphorus in the urine. PTH also stimulates the kidneys to produce active vitamin D, which then tells the intestines to absorb more calcium from food^[4].

In chronic kidney disease, this system breaks down. The damaged kidneys cannot make enough active vitamin D, so the intestines cannot absorb calcium properly. The kidneys also fail to remove phosphorus effectively, causing it to build up. When calcium levels fall or phosphorus levels rise, the parathyroid glands receive constant signals to make more PTH. Over months and years of responding to these signals, the parathyroid glands grow larger, a process called hyperplasia^[4].

The increased PTH pulls more and more calcium from the bones, weakening them and leading to a condition called renal osteodystrophy, where bones become deformed and prone to fractures. The excess PTH also contributes to calcium deposits forming in blood vessels, the heart, and other soft tissues throughout the body. These calcium deposits in blood vessels can lead to cardiovascular problems, which are a major cause of illness and death in people with advanced kidney disease^[4].

When vitamin D deficiency is the cause, the mechanism is similar but without the kidney failure component. Without adequate vitamin D, calcium absorption from the intestines drops. Low blood calcium triggers the parathyroid glands to release more PTH. If the vitamin D deficiency is not corrected, the parathyroid glands continue working overtime and eventually enlarge^[5].

Diagnosis and Monitoring

Diagnosing secondary hyperparathyroidism typically begins with blood tests. A healthcare provider will measure calcium, phosphorus, and PTH levels in the blood. In secondary hyperparathyroidism, PTH levels are elevated while calcium levels are usually low or normal. Phosphorus levels are often high, especially in people with kidney disease^[4].

Vitamin D levels are also measured to determine if vitamin D deficiency is contributing to the problem. Kidney function tests help assess whether chronic kidney disease is the underlying cause^[4].

Additional tests may include bone density scans to check for bone weakening and damage. Imaging tests can look for calcium deposits in blood vessels or soft tissues^[10].

Treatment Approaches

The best treatment for secondary hyperparathyroidism aims to fix the underlying cause. For people with vitamin D deficiency, raising vitamin D levels to the normal range through supplements or increased sun exposure often resolves the condition. The parathyroid glands can return to normal size and function once vitamin D and calcium levels stabilize^[5].

For people with chronic kidney disease, treatment is more complex because the kidney damage usually cannot be reversed. A kidney transplant is the only treatment that truly fixes the underlying problem. After a successful transplant, many people see improvement in their secondary hyperparathyroidism, though some degree of overactive parathyroid function may persist^[5].

When the underlying cause cannot be fixed, medical therapy becomes the main approach. For people with kidney disease, treatment includes several components. Phosphate binders are medications taken with meals that bind to phosphorus in food, preventing the body from absorbing it. This helps lower blood phosphorus levels. These binders can be calcium-based or non-calcium based^[7].

Active vitamin D supplements, such as calcitriol, doxercalciferol, or paricalcitol, help the intestines absorb calcium and also signal the parathyroid glands to reduce PTH production. A newer medication called extended-release calcifediol was recently approved for treating secondary hyperparathyroidism in people with early-stage chronic kidney disease who have low vitamin D levels^[7].

Calcimimetics are drugs that trick the parathyroid glands into thinking calcium levels are higher than they actually are, causing them to produce less PTH. One such medication, Sensipar, can lower PTH levels by about 50% on average. However, these medications can cause side effects including nausea and vomiting^[5].

Dietary changes play an important role. People with kidney disease often need to limit phosphorus intake by avoiding high-phosphorus foods such as dairy products, nuts, beans, and processed foods with phosphate additives^[7].

Surgery may be necessary when medical therapy does not work adequately. Up to 25% of people with kidney failure do not respond well enough to medications. Surgery is considered when bone density continues to worsen, when severe itching cannot be controlled, when calciphylaxis develops, when PTH levels remain consistently above 800 pg/ml despite treatment, or when calcium and phosphorus levels cannot be controlled even with dialysis^[5].

Three main types of surgery are used. Subtotal parathyroidectomy involves removing three and a half of the four parathyroid glands. Total parathyroidectomy with autotransplantation means removing all four glands and placing a small piece of one parathyroid in the forearm, where it can continue to produce some PTH. PTH-guided parathyroidectomy involves removing enough parathyroid tissue to bring PTH levels down to between 200 and 300 during the operation. Each approach has advantages and disadvantages, and the choice depends on individual circumstances^[5].

It’s important to understand that surgery does not fix the underlying kidney disease or vitamin D problems. Because the root cause remains, there is a high risk that secondary hyperparathyroidism will return after surgery^[5].