Hypercalcaemia


Hypercalcemia, also spelled hypercalcaemia, is a high calcium level in the blood serum. The normal range for total calcium is 2.1–2.6 mmol/L, with levels greater than 2.6 mmol/L defined as hypercalcemia. Those with a mild increase that has developed slowly typically have no symptoms. In those with greater levels or rapid onset, symptoms may include abdominal pain, bone pain, confusion, depression, weakness, kidney stones or an abnormal heart rhythm including cardiac arrest.
Most outpatient cases are due to primary hyperparathyroidism and inpatient cases due to cancer. Other causes of hypercalcemia include sarcoidosis, tuberculosis, Paget disease, multiple endocrine neoplasia, vitamin D toxicity, familial hypocalciuric hypercalcaemia and certain medications such as lithium and hydrochlorothiazide. Diagnosis should generally include either a corrected calcium or ionized calcium level and be confirmed after a week. Specific changes, such as a shortened QT interval and prolonged PR interval, may be seen on an electrocardiogram.
Treatment may include intravenous fluids, furosemide, calcitonin, intravenous bisphosphonate, in addition to treating the underlying cause. The evidence for furosemide use, however, is poor. In those with very high levels, hospitalization may be required. Haemodialysis may be used in those who do not respond to other treatments. In those with vitamin D toxicity, steroids may be useful. Hypercalcemia is relatively common. Primary hyperparathyroidism occurs in 1–7 per 1,000 people, and hypercalcaemia occurs in about 2.7% of those with cancer.

Signs and symptoms

The neuromuscular symptoms of hypercalcaemia are caused by a negative bathmotropic effect due to the increased interaction of calcium with sodium channels. Since calcium blocks sodium channels and inhibits depolarization of nerve and muscle fibers, increased calcium raises the threshold for depolarization. This results in decreased deep tendon reflexes, and skeletal muscle weakness.
Other symptoms include cardiac arrhythmias, fatigue, nausea, vomiting, loss of appetite, abdominal pain, & paralytic ileus. If kidney impairment occurs as a result, manifestations can include increased urination, urination at night, and increased thirst. Psychiatric manifestation can include emotional instability, confusion, delirium, psychosis, and stupor. Calcium deposits known as limbus sign may be visible in the eyes.
Symptoms are more common at high calcium blood values. Severe hypercalcaemia is considered a medical emergency: at these levels, coma and cardiac arrest can result. The high levels of calcium ions decrease the neuron membrane permeability to sodium ions, thus decreasing excitability, which leads to hypotonicity of smooth and striated muscle. This explains the fatigue, muscle weakness, low tone and sluggish reflexes in muscle groups. The sluggish nerves also explain drowsiness, confusion, hallucinations, stupor or coma. In the gut this causes constipation. Hypocalcaemia causes the opposite by the same mechanism.

Hypercalcaemic crisis

A hypercalcaemic crisis is an emergency situation with a severe hypercalcaemia, generally above approximately 14 mg/dL.
The main symptoms of a hypercalcaemic crisis are oliguria or anuria, as well as somnolence or coma. After recognition, primary hyperparathyroidism should be proved or excluded.
In extreme cases of primary hyperparathyroidism, removal of the parathyroid gland after surgical neck exploration is the only way to avoid death. The diagnostic program should be performed within hours, in parallel with measures to lower serum calcium. Treatment of choice for acutely lowering calcium is extensive hydration and calcitonin, as well as bisphosphonates.

Causes

and malignancy account for about 90% of cases of hypercalcaemia.
Causes of hypercalcemia can be divided into those that are PTH dependent or PTH independent.

Parathyroid function

Hypercalcemia of malignancy is due to a variety of mechanisms. The two most common are humoral hypercalcemia of malignancy and local osteolytic hypercalcemia due to bony metastasis. Humoral hypercalcemia of malignancy involves the tumor releasing a hormone which increases calcium mobilization into the circulation. PTHrP acts similarly to parathyroid hormone in that it binds to the parathyroid hormone 1 receptors on the kidneys and bones and causes an increased tubular reabsorption of calcium and activation of osteoclast activity, respectively. Osteoclasts are a type of bone cell which cause bone resorption, releasing calcium into the bloodstream. PTHrP also acts by activating rank ligand and inhibiting osteoprotegerin which activates nuclear factor kappa B, which causes further activation of osteoclast activity. The combination of PTHrP driven osteoclast activation and calcium reabsorption by the kidneys causes hypercalcemia associated with malignancy.
Another mechanism in which cancer causes hypercalcemia is via local osteolysis due to metastasis to bone. Tumor bone metastasis releases local cytokines including IL-6, IL-8, IL-11, interleukin-1 beta, TNF alpha and macrophage inflammatory protein. These cytokines activate osteoclasts and inhibit osteoblasts via the rank ligand pathway leading to bone resorption and calcium release into the bloodstream. The massive release of calcium from bone metastasis and osteoclast activation usually overwhelms the kidney's ability to secrete calcium, thus leading to hypercalcemia.
Hypercalcemia of malignancy may also occur due to tumor production of vitamin D or parathyroid hormone. These causes are rare and constitute about 1% of all causes of hypercalcemia of malignancy.
Hypercalcemia of malignancy usually portends a poor prognosis, and the medial survival is 25–52 days of its development. It has an incidence of 30% in those with cancer, and the prevalence is estimated to be about 2-3% in the United States.
Image:Small cell carcinoma of the ovary hypercalcemic type - high mag.jpg|thumb|right|Micrograph of ovarian small cell carcinoma of the hypercalcemic type. H&E stain.
Common cancer types that are associated with hypercalcemia of malignancy include:
Diagnosis should generally include either a calculation of corrected calcium or direct measurement of ionized calcium level and be confirmed after a week. This is because either high or low serum albumin levels does not show the true levels of ionised calcium. There is, however, controversy around the usefulness of corrected calcium as it may be no better than total calcium.
Once calcium is confirmed to be elevated, a detailed history taken from the subject, including review of medications, any vitamin supplementations, herbal preparations, and previous calcium values. Chronic elevation of calcium with absent or mild symptoms often points to primary hyperparathyroidism or Familial hypocalciuric hypercalcemia. For those who has underlying malignancy, the cancers may be sufficiently severe to show up in history and examination to point towards the diagnosis with little laboratory investigations.
If detailed history and examination does not narrow down the differential diagnoses, further laboratory investigations are performed. Intact PTH is measured with immunoradiometric or immunochemoluminescent assay. Elevated iPTH with high urine calcium/creatinine ratio is suggestive of primary hyperparathyroidism, usually accompanied by low serum phosphate. High iPTH with low urine calcium/creatinine ratio is suggestive of familial hypocalciuric hypercalcemia. Low iPTH should be followed up with Parathyroid hormone-related protein measurements. Elevated PTHrP is suggestive of malignancy. Normal PTHrP is suggestive of multiple myeloma, vitamin A excess, milk-alkali syndrome, thyrotoxicosis, and immobilisation. Elevated Calcitriol is suggestive of lymphoma, sarcoidosis, granulomatous disorders, and excessive calcitriol intake. Elevated calcifediol is suggestive of vitamin D or excessive calcifediol intake.
The normal range is 2.1–2.6 mmol/L, with levels greater than 2.6 mmol/L defined as hypercalcaemia. Moderate hypercalcaemia is a level of 2.88–3.5 mmol/L while severe hypercalcaemia is > 3.5 mmol/L.

ECG

Abnormal heart rhythms can also result, and ECG findings of a short QT interval suggest hypercalcaemia. Significant hypercalcaemia can cause ECG changes mimicking an acute myocardial infarction. Hypercalcaemia has also been known to cause an ECG finding mimicking hypothermia, known as an Osborn wave.