“Hypercalcaemia in dogs and cats: an Overview” is a webinar that you can enjoy during the congress week thanks to NationWide Laboratories, presented by Dr Stacey A. Newton. Hypercalcaemia is a common finding in both dogs and cats, however, it presents differently in both species.
At the end of the webinar, you will be aware of the clinical symptoms, the pathogenesis of the disease and its types, whether it is parathyroid-dependent or parathyroid-independent. In addition, you will learn about diagnosis, management, submission and treatment.
Dr Stacey begins the presentation with an introduction to Calcium, where she explains how calcium in the blood is made up of three parts, where 55% is the biologically active part called ionised calcium and this is what we veterinarians should concentrate on. In dogs and cats the calcium levels are quite similar, with cats having slightly less compared to dogs.
The hormones that play an important role in calcium regulation are parathyroid hormone, calcitrol and calcitonin. The first two are the most important in these species.
Hypercalcaemia can occur primarily due to:
- Increase bone mobilisation of Ca
- Decrease urinary Ca loss
In a patient with a functional parathyroid gland, the parathyroid receives negative feedback from calcium and phosphorus and it decreases PTH production, if there is an increase in Ca and P, a decrease in PTH production will occur, Ca and P also create negative feedback in the kidneys having an impact on vitamin D, which subsequently has an impact on bones and the gut.
The webinar also discusses Vitamin D and how it is a mixture of several compounds, not just D3. In a patient with Hypercalcaemia D3 and D2 are going to be very significant and the most important. It should be noted that unlike other species, cats, being carnivores, they can only metabolise vitamin D3, so supplementation with other types of vitamin D is likely to have minimal effect on calcium levels.
The primary cause of hypercalcaemia is hyperparathyroidism, which is an abnormality of the parathyroid gland, it is uncommon and is usually unilateral and most commonly involves an adenoma of the gland.
The secondary cause is Parathyroid independent hypercalcaemia, there are many processes that result in this, for example, one of the most common in dogs is associated with malignant tumours.
There are also transient causes, such as a patient arriving dehydrated, or with hyperadrenocorticism, among others. And it also occurs due to non-pathological causes such as laboratory error and poorly fed animals.
In cats the most common cause of hypercalcaemia is idiopathic, and we do not know the pathogenic cause of this.
The webinar continues by giving examples of diseases related to each species, the signs and the most important characteristics. It then outlines a list of clinical signs that we can see according to the species, for example, in dogs the most common clinical signs are polyuria, polydipsia, anorexia, lethargy and weakness. In cats the most common clinical sign is anorexia, and less common is vomiting, depression, weakness, constipation and PU/PD. It should be noted that the clinical signs will depend on how high the ionised calcium is.
We will know the diagnosis from ionised calcium, not total calcium. After confirming that we have high ionised calcium, we need to measure PTH. If we suspect hypercalcaemia due to a malignant tumour, we can measure PTHrP and if we suspect vitamin D toxicity, 25 hydroxyvitamin D should be measured.
In the treatment of a patient with hypercalcemia, if calcium levels are too high it is necessary to weigh up whether to medicate immediately or to wait for a specific diagnosis to see what is causing it. Treatment will depend on the cause, hence the importance of always trying to make a specific diagnosis.
If you want to learn more about hypercalcaemia, I highly recommend watching this webinar! Don’t miss the amazing webinars we have all week in our virtual congress 2022!