A parathyroid adenoma is a small, benign tumor on one of your four parathyroid glands that causes it to produce too much parathyroid hormone (PTH). This excess hormone pulls calcium from your bones into your bloodstream, leading to a condition called primary hyperparathyroidism. About 85% of all primary hyperparathyroidism cases are caused by a single parathyroid adenoma, and less than 1% turn out to be cancerous.
What the Parathyroid Glands Normally Do
Your four parathyroid glands sit behind your thyroid in your neck, each roughly the size of a grain of rice. Their job is straightforward: monitor calcium levels in your blood and release PTH when calcium drops too low. PTH then signals your bones to release stored calcium, your kidneys to hold onto calcium instead of flushing it out, and your gut to absorb more calcium from food. When blood calcium rises back to normal, the glands sense this and dial PTH production back down.
An adenoma breaks this feedback loop. The tumor cells keep producing PTH even when blood calcium is already high. Over time, this drives calcium levels up and weakens bones as they continuously lose their mineral stores.
Who Gets Parathyroid Adenomas
Primary hyperparathyroidism is the third most common endocrine disorder, with an incidence ranging from 0.4 to 82 cases per 100,000 people per year depending on the population studied. It overwhelmingly affects women, particularly around and after menopause. In Scandinavian women of perimenopausal and postmenopausal age, prevalence reaches 2 to 5%, compared to about 0.73% in elderly men.
Symptoms and What High Calcium Feels Like
Nearly half of people with a parathyroid adenoma have no obvious symptoms at the time of diagnosis. Many are discovered incidentally during routine blood work or while being evaluated for an unrelated thyroid problem. When symptoms do appear, they tend to creep in gradually and affect several body systems at once.
The kidneys are often hit first. Excess calcium in the blood gets filtered into urine, where it can crystallize into kidney stones. In one clinical series, about 13% of patients presented with kidney stones alone, and another 16% had both kidney and bone problems simultaneously. Bone pain, weakened bones, and even fractures can develop as PTH continuously drains calcium from the skeleton. A meta-analysis found that people with primary hyperparathyroidism have a 2.6 times higher risk of vertebral fractures and a 1.7 times higher risk of fractures overall compared to people with normal parathyroid function.
Beyond the kidneys and bones, high calcium can cause nausea, vomiting, and chronic pancreatitis. Many people notice subtler problems: fatigue, muscle weakness, difficulty concentrating, or mood changes often described as “mental fog.” These neuropsychiatric symptoms are easy to dismiss as stress or aging, which is one reason parathyroid adenomas often go undiagnosed for years.
How It’s Diagnosed
The hallmark finding is high blood calcium paired with a PTH level that is either elevated or “inappropriately normal.” Normally, when calcium is high, PTH should drop to near zero. If your calcium is above the normal range and your PTH hasn’t suppressed, the parathyroid glands are the likely culprit. In some cases, calcium levels exceed 14 mg/dL and PTH rises to many times its normal value, though most adenomas produce milder elevations.
Once blood tests confirm the diagnosis, imaging helps pinpoint which gland is affected before surgery. The two most common techniques are a sestamibi scan (a nuclear medicine study where a small amount of radioactive tracer is injected and taken up preferentially by overactive parathyroid tissue) and a specialized CT scan called 4D-CT. Both perform similarly well: sestamibi scans have a sensitivity of about 85% and specificity of 95%, while 4D-CT shows a sensitivity of 81% and specificity of 94%. When both are used together, the chance of correctly identifying the adenoma’s location improves further.
Surgery: The Primary Treatment
Removing the adenoma is the only cure. Modern parathyroid surgery has shifted heavily toward minimally invasive approaches, which use a small incision in the neck rather than the traditional open exploration of all four glands. Cure rates for these procedures are consistently high. In published series ranging from 107 to 394 cases, success rates fall between 98.1% and 98.5%, with “cure” defined as a return to normal calcium levels that holds over follow-up.
Complications are uncommon. In one large series of 350 minimally invasive cases, transient low calcium after surgery occurred in 2.7% of patients. Permanent vocal cord nerve injury, which can cause hoarseness, occurred in 0.8% of cases. Postoperative bleeding was rare at 0.3%. Most people go home the same day or the next morning.
Hungry Bone Syndrome
After the adenoma is removed and PTH drops suddenly, bones that have been starved of calcium can rapidly pull it back from the bloodstream. This rebound drop in blood calcium is called hungry bone syndrome. It causes tingling in the fingers and around the mouth, muscle cramps, and in severe cases, spasms. The risk is highest in people who had very elevated PTH levels or significant bone disease before surgery. Calcium and vitamin D supplements are given after the procedure to cushion this transition, and bone density at the spine and hip improves measurably in the months and years following a successful operation.
When Surgery Isn’t an Option
For people who can’t undergo surgery due to other health conditions or high surgical risk, medication can help manage calcium levels without removing the adenoma. Cinacalcet is the primary drug used in this situation. It works by making the parathyroid glands more sensitive to calcium, tricking them into producing less PTH. It does not shrink the adenoma or cure the underlying condition, but it can bring calcium levels down to a safer range. People who go this route need ongoing blood monitoring because the adenoma remains in place and can slowly grow.
Adenoma vs. Carcinoma
The vast majority of parathyroid tumors are benign adenomas. Parathyroid carcinoma accounts for less than 1% of primary hyperparathyroidism cases. Carcinomas tend to produce dramatically higher calcium and PTH levels than adenomas, and the tumors are often larger and may feel firm or be attached to surrounding tissue. In a study of parathyroid masses weighing more than 3.5 grams, only 2 out of 21 turned out to be cancer. A small percentage of large tumors show atypical features under the microscope that aren’t clearly benign or malignant, but even among tumors weighing 2 grams or more, atypical adenomas are far more common than true carcinomas (17.5% vs. 1.3%).
Long-Term Outlook
After successful surgery, most people see their calcium and PTH levels normalize within hours to days. Bone density improves over the following one to two years, particularly at the spine and hip. Kidney stone risk drops significantly once calcium levels return to normal. For the roughly half of patients who were asymptomatic before surgery, many report improvements in energy, mood, and concentration they didn’t realize they were missing, a pattern so common that surgeons sometimes describe it as patients not knowing how poorly they felt until after recovery.
Recurrence after removal of a single adenoma is uncommon but possible, occurring in roughly 1 to 2% of cases. Periodic calcium checks in the years after surgery help catch any recurrence early.