Page 314 - WSAVA2018
P. 314

 25-28 September, 2018 | Singapore
J. Beatty1
1University of Sydney, Sydney School of Veterinary Science, Camperdown, Australia
Hypercalcaemia in cats- update on diagnosis and treatment
Professor Julia Beatty
Faculty of Veterinary Science, University of Sydney, NSW 2006
Diagnostic investigation for ionised hypercalcaemia may be prompted by total hypercalcaemia on a biochemical profile, urolithiasis, neoplasia, constipation or undiagnosed non-specific signs, even when total serum calcium (tCa) is normal. Ionized hypercalcaemia has deleterious long-term consequences and should be managed even in asymptomatic patients.
Differential diagnoses for hypercalcaemia in the cat
Idiopathic hypercalcaemia (IHC) is the most common cause of ionized hypercalcaemia in cats. Cats of
any age can be affected. Long-haired cats are over- represented. IHC is characterised by mild to moderate hypercalcaemia, normophosphataemia and an appropriate parathyroid response (i.e. ↓PTH). Clinical signs vary with the degree of hypercalcaemia but around 50% of cats are asymptomatic. The diagnosis is made by excluding other causes.
Chronic kidney disease (CKD) is a common cause of total hypercalcaemia. In renal azotaemia, the complexed calcium fraction is usually increased while the ionized fraction is normal. In the azotaemic patient with elevated tCa, measurement of iCa is indicated. If iCa is normal then no further investigation of the hypercalcaemia is required. However, if iCa is elevated in an azotaemic patient, ionized hypercalcaemia may be contributing
to the renal dysfunction. Further investigation of hypercalcaemia is indicated. Phosphate-binder use should be reviewed as long-term use of aluminum- based phosphate-binders can cause toxicity which resembles idiopathic hypercalcaemia. Resolution may take months after medication withdrawal. Calcium, particularly carbonate- based binders, should be withdrawn as should calcitriol therapy. A rare differential in the setting of ionized hypercalcaemia and azotaemia is tertiary hyperparathyroidism, where the set-point of the parathyroid glands is increased in advanced CKD (↑ iCa ↑PTH).
Humoral hypercalcaemia of malignancy (HHM) results when tumour-derived parathyroid hormone-related peptide (PTHrP) or other mediators mimick the action
of PTH. HHM is less common in cats than dogs. Feline HHM is reported in head, neck and bronchopulmonary carcinomas, lymphoma, osteosarcoma, fibrosarcoma and multiple myeloma.
Primary hyperparathyroidism is rare in cats. Most cases are over 8 years of age. Adenomas are most common, but hyperplasia and carcinoma are reported. Involvement of more than one gland is unusual. Cervical masses are palpable in 50% of cases. A high or normal PTH in the face of ionized hypercalcaemia is consistent with autonomous secretion from the parathyroid gland. Low or normal serum phosphate is expected in primary hyperparathyroidism and HHM. Ultrasound may assist
in detecting parathyroid lesions. Surgical patients undergoing parathyroidectomy should be monitored closely for post-operative hypocalcaemia because of feedback atrophy of the remaining glands.
Hypervitaminosis D. Sources of vitamin D
intoxication include dietary, rodenticide ingestion,
certain houseplants (Cestrum diurnum), calcitriol supplementation and ingestion of analogues (e.g. calcipotriene). Commercial assays measure 25-OH cholecalciferol (calcidiol). Calcitirol assays are less widely available. Vitamin D analogues may not be detected by these assays. PTH and PTHrP are low or undetectable
in hypervitaminosis D. If cholecalciferol or ergocalciferol have been ingested, calcidiol levels will be elevated
for weeks because of lipid storage. Calitriol levels are normal or occasionally increased. In calcitriol toxicity, calcidiol levels will be normal. Calcitriol may be increased or, because it has a short half life in circulation, levels may be normal.
Granulomatous disease. Activated macrophages can convert calcidiol to calcitriol. Hypercalcaemia has been reported in occasional cases of nocardial, mycobacterial, cryptococcocal, blastomycosis, histoplasmosis and actinomycetal infection.
Hypoadrenocorticism is a rare endocrinopathy of cats and <10% of cases have hypercalcaemia.
Signs associated with hypercalcaemia
Clinical signs may relate to the hypercalcaemia itself
and any underlying disease. Signs associated with ionized hypercalcaemia range from inapparent to
severe depending on the rate and the magnitude of
iCa elevation. Lethargy, anorexia and vomiting are most common followed by polyuria/polydipsia (PUPD), lower urinary tract signs (e.g. stranguria, haematuria, pollakiuria, periuria from urinary tract infection, inflammation or obstruction), weight loss, weakness and tremors. Constipation has been associated with hypercalcaemia in cats. Severe ionized hypercalcaemia can cause obtundation, arrhythmias, seizures and death.

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