Hypercalcemia

30 Hypercalcemia



David L. Panciera



1. What is the significance of an elevated total calcium concentration?

The total serum calcium concentration is routinely measured on serum biochemical analyses. It consists of 3 components. Ionized calcium, the physiologically active form in the circulation, normally accounts for approximately 55% of total calcium. Ionized calcium is important in regulating physiologic functions and in control of parathyroid hormone (PTH) secretion. Approximately 35% of calcium is bound to plasma proteins, and 10% (so-called complexed calcium) is bound to anions, including phosphate, bicarbonate, citrate, sulfate, and lactate. Alterations in plasma protein concentration, blood pH, and anion concentrations can alter total calcium concentration without affecting ionized calcium. Conversely, these factors can affect the concentration of ionized calcium without altering that of total calcium. Therefore an elevated concentration of total calcium does not always reflect an elevated concentration of ionized calcium.


2. What are the important clinical consequences of hypercalcemia?

Hypercalcemia induces polyuria by inhibiting the action of antidiuretic hormone on the collecting tubules. Hypercalcemia also impairs renal function by reducing glomerular blood flow through afferent arteriolar vasoconstriction. Hypercalcemia can cause permanent renal dysfunction by inducing renal mineralization, vasoconstriction, and other mechanisms. Calcium-containing uroliths are common in dogs with chronic hypercalcemia. The decreased neuromuscular excitability induced by hypercalcemia can cause weakness, muscle tremors, constipation, and vomiting.


3. What are the common clinical signs of hypercalcemia?

Polyuria and polydipsia are the most common clinical signs of hypercalcemia. Lethargy, inappetence, vomiting, weakness, muscle tremors, and constipation also occur. Signs of lower urinary tract inflammation may be present in dogs with cystic calculi that results from hypercalcemia. Other clinical signs may be present, related either to the primary disease process or to renal failure induced by the hypercalcemia.


4. What are the most common causes of hypercalcemia?

Neoplasia is the most common cause of hypercalcemia, with lymphoma, apocrine gland adenocarcinoma of the anal sac, multiple myeloma, and thyroid carcinoma being the most common. Renal failure is a common cause of elevated total calcium, although the concentration of ionized calcium is usually normal or low. Some dogs with hypoadrenocorticism have mild hypercalcemia. Primary hyperparathyroidism is an uncommon cause of hypercalcemia, and is usually secondary to a solitary parathyroid adenoma or parathyroid gland hyperplasia secreting excessive parathyroid hormone (PTH). Vitamin D intoxication can occur due to ingestion of vitamin D rodenticides, certain plants containing vitamin D compounds, or vitamin D–containing medications. Occasionally, osteolytic lesions can cause a mild increase in serum calcium concentration. Granulomatous diseases, particularly systemic mycoses (blastomycosis), and schistosomiasis can cause hypercalcemia. Laboratory error should always be considered as a cause of a reported elevated serum calcium concentration.


5. What diagnostic testing should be considered when evaluating a dog with hypercalcemia?

The first step is to confirm the hypercalcemia by obtaining another blood sample. Review of a complete history and physical examination, including careful rectal palpation for anal sac or sublumbar lymph node enlargement, usually helps direct further diagnostic testing. Routine complete blood count (CBC), serum chemistry testing, and urinalysis are indicated in every case. The CBC may provide evidence of inflammation associated with granulomatous disease, osteomyelitis, or neoplasia, or of leukemia. Test results may provide some indication of the underlying cause, for example elevated renal values (indicating renal failure), electrolyte abnormalities (indicating hypoadrenocorticism), elevated alkaline phosphatase (ALP) activity (indicating neoplasia or primary hyperparathyroidism), and plasma protein concentration (indicating lymphoid neoplasia or chronic inflammation). Hypophosphatemia or low-normal concentrations of phosphate frequently occur with hypercalcemia due to malignancy and primary hyperparathyroidism, whereas hyperphosphatemia is often found in cases of renal failure and vitamin D toxicosis. Abnormalities identified on the physical examination should be further evaluated by an appropriate method such as fine needle aspiration, biopsy, abdominal radiographs, or ultrasound, as indicated. Thoracic radiographs should be considered early in the diagnostic process, because mediastinal lymphosarcoma is often associated with hypercalcemia. A cause of hypercalcemia is identified in most cases using this approach.

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Jul 31, 2016 | Posted by in INTERNAL MEDICINE | Comments Off on Hypercalcemia

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