A thyroid nodule is a lump in the neck formed by a growth of cells within the thyroid gland, which produces hormones regulating metabolism. While the thyroid does produce a hormone that affects calcium, a direct link between a nodule and high calcium levels (hypercalcemia) is rare. The most frequent connection between a neck lump and hypercalcemia is often indirect, involving a separate set of glands located nearby. Determining the true source of the calcium imbalance requires precise investigation.
Defining Thyroid Nodules and Hypercalcemia
A thyroid nodule is a lump or growth that develops within the thyroid gland. These growths are common, with most people developing at least one small nodule by middle age. Nodules may be solid tissue, fluid-filled cysts, or a combination of both, and the vast majority are benign.
Hypercalcemia is the medical term for an abnormally high concentration of calcium in the bloodstream. Maintaining calcium within a narrow range is important for nerve and muscle function, and chronic hypercalcemia can weaken bones and affect kidney function.
Direct Causation: When the Nodule Itself Raises Calcium
Instances where a thyroid nodule directly causes hypercalcemia are rare. The most direct link involves Medullary Thyroid Carcinoma (MTC), a specific type of thyroid malignancy. This cancer arises from the parafollicular C cells, which produce the hormone calcitonin.
Calcitonin generally acts to lower blood calcium levels. However, in MTC, the cancerous nodule secretes excessive amounts of calcitonin, leading to hypercalcitoninemia. While this massive overproduction of calcitonin does not typically lead to low calcium levels, the nodule itself is the source of the hormonal imbalance.
Rarely, other hyperfunctioning nodules that produce excessive thyroid hormone may contribute to hypercalcemia by increasing bone turnover, which releases calcium into the blood. In these cases, the elevated calcium is secondary to the hyperthyroidism caused by the nodule.
Indirect Causation: The Role of the Parathyroid Glands
The most frequent reason a person with a neck lump has high calcium involves the parathyroid glands. These four pea-sized glands are located immediately behind the thyroid gland and are functionally distinct, regulating the body’s calcium levels. They achieve this by producing Parathyroid Hormone (PTH), which acts on the bones, kidneys, and intestines to increase calcium in the blood.
If one or more parathyroid glands become overactive, often due to a benign growth called an adenoma, it results in Primary Hyperparathyroidism (PHPT). PHPT is the leading cause of hypercalcemia in the general population. An enlarged parathyroid gland or adenoma can be located directly adjacent to the thyroid, which is often the source of confusion with a thyroid nodule on imaging like ultrasound.
PHPT is diagnosed based on elevated calcium levels alongside elevated or inappropriately normal PTH levels, confirming the parathyroid gland as the source.
Diagnostic Steps to Pinpoint the Source
When a patient presents with both a neck lump and hypercalcemia, the diagnostic process must precisely determine the origin of the problem. Initial blood work is essential, starting with a measurement of the serum calcium level, often repeated to confirm the persistent elevation, followed by checking the level of Parathyroid Hormone (PTH). An elevated PTH level alongside high calcium strongly suggests PHPT, indicating the parathyroid glands are the source.
If PTH levels are suppressed, less common causes, including direct thyroid issues, are considered. In this case, a calcitonin blood test screens for Medullary Thyroid Carcinoma, as a significantly elevated level marks this malignancy. Specialized imaging then locates the physical source.
A neck ultrasound visualizes the thyroid, nodules, and surrounding parathyroid glands. If PHPT is confirmed biochemically, a Sestamibi scan may be used. This nuclear medicine test helps locate overactive parathyroid tissue, as the tracer persists longer in an abnormal gland than in normal thyroid tissue.