The veterinary nurse’s guide to parathyroid disorders
How often do you see parathyroid disorders in practice?
Though not as commonly encountered as other endocrine diseases, it’s really important for us as veterinary nurses to be able to spot the signs of parathyroid disorders and know how to nurse and treat these patients.
This is particularly important in patients with hypoparathyroidism - as these patients can present with potentially life-threatening hypocalcaemia.
Today we’re talking all about what the parathyroid glands do, their vital role in calcium homeostasis, and what happens when they go wrong - as well as how to diagnose, treat and nurse patients with parathyroid disorders.
The Parathyroid Glands
There are two parathyroid glands sitting next to the thyroid glands, either side of the ventral neck, next to the cervical trachea.
These release parathyroid hormone (PTH), which regulates blood calcium levels.
Normally, hypocalcaemia stimulates the release of PTH from the parathyroid glands, and hypercalcaemia reduces the amount of PTH released.
PTH converts vitamin D to its active form, vitamin D3. This increases blood calcium levels through several methods:
It increases the absorption of calcium from the gastrointestinal tract
It increases the conservation of calcium in the kidneys
It increases the release of calcium from bony stores
The ultimate goal and overall effect of PTH release is to increase blood calcium levels back to within normal limits.
When this goes wrong, patients can present to us with either hypoparathyroidism or hyperparathyroidism. The clinical signs we see vary between the two diseases, and nurses play a key role in the diagnosis and treatment of both conditions.
Hypoparathyroidism
Hypoparathyroidism is the loss of functional parathyroid tissue.
It can be a primary (naturally occurring) or an iatrogenic disease.
Pathophysiology
In primary (naturally occurring) hypoparathyroidism, the immune system causes destruction of parathyroid tissue. This is most common in dogs and is particularly seen in toy poodles.
Iatrogenic hypoparathyroidism can be seen following a thyroidectomy if the parathyroid is removed or damaged during surgery, or following treatment for primary hyperparathyroidism.
Clinical Signs
The clinical signs of hypoparathyroidism are associated with hypocalcaemia, and are primarily neuromuscular, since calcium plays a key role in the transmission of nerve impulses to muscles.
Signs include:
Muscle tremors
Weakness
Ataxia
Lethargy
Facial rubbing/itching
Seizures
Behavioural Changes
Diagnosis
A number of different diagnostic tests are performed in patients with suspected hypoparathyroidism, including:
Ionised calcium levels (this is the freely available calcium circulating in the bloodstream)
Total calcium levels (this includes both ionised calcium and calcium bound to plasma proteins)
Parathyroid hormone levels.
Other diagnostic tests performed after stabilisation of hypocalcaemia include parathyroid hormone levels.
PTH samples have very specialised sampling, handling and transport requirements, and the veterinary nurse must be aware of these when taking blood from the patient.
When measuring PTH levels the blood must be:
Collected into a frozen syringe
Placed in frozen EDTA tubes
Immediately centrifuged
The EDTA plasma is then separated into a frozen plain tube
The sample must then be frozen
It must be sent to the laboratory in a special frozen transport pack, available to borrow from the laboratory.
Treatment and Nursing Care
Treatment initially involves correction of hypocalcaemia, usually by intravenous administration initially if calcium levels are severely low, followed by the administration of calcitriol (vitamin D3) and calcium carbonate.
IV calcium administration must be performed with care, as cardiac arrhythmias are common, so continuous ECG monitoring is recommended.
Nursing care of the hypoparathyroid patient in the hospital involves careful monitoring of their heart rate and rhythm and the prompt identification of arrhythmias if they are receiving IV calcium.
Monitoring for signs of hypocalcaemia is also vital, and a ‘hypocalcaemia plan’ and an emergency pack containing doses, drugs, needles, syringes and monitoring equipment should be on-hand near to the patient.
These patients often require regular follow-up visits for blood sampling to recheck their calcium levels, and the veterinary nurse can perform these in a nurse clinic, alongside collecting an updated clinical history and examining the patient.
Hyperparathyroidism
Hyperparathyroidism is an abnormal increase in the amount of functional parathyroid tissue. This can be a primary disease or occur secondary to renal disease.
Pathophysiology
Primary hyperparathyroidism occurs most commonly in dogs, and is associated with a benign tumour on the pituitary gland, releasing excessive amounts of parathyroid hormone. It is commonly seen in Keeshonds and Labrador retrievers.
Secondary renal hyperparathyroidism is a rare but well-documented complication of renal disease.
As kidney disease progresses, the body becomes less able to excrete phosphorus and blood phosphate levels increase. As calcium and phosphate are inversely related, when phosphate levels rise, calcium levels fall - as phosphate binds to calcium, reducing the amount of calcium available in the bloodstream.
This causes hypocalcaemia, which causes the parathyroid glands to increase PTH secretion, as they try to increase calcium levels back up to normal.
Clinical Signs
The clinical signs of primary hyperparathyroidism are associated with hypercalcaemia. The most common signs we see are polyuria and polydipsia; we may also see lethargy and weight loss.
Diagnosis
Diagnosis is achieved via blood tests and ultrasonography:
Total and ionised calcium levels are increased in cases of primary hyperparathyroidism.
Calcium levels are low in cases of secondary renal hyperparathyroidism.
Phosphate levels are typically normal to low in primary hyperparathyroidism and high in secondary renal hyperparathyroidism.
Evidence of azotaemia (increases in creatinine + BUN) will be present in cases of secondary renal hyperparathyroidism.
Elevated PTH levels provide a definitive diagnosis.
Ultrasound may be performed - scanning the neck allows a parathyroid nodule to be identified in cases of primary hyperparathyroidism, and scanning the abdomen allows us to examine the kidneys and evaluate the presence and severity of any renal disease present.
Treatment and Nursing Care
Treatment initially revolves around reducing calcium levels. This is achieved with intravenous fluid therapy, usually with 0.9% Saline (+/- added potassium), since Hartmann’s solution contains calcium.
Diuretics +/- steroids +/- bisphosphonates may also be used depending on the individual patient and degree of hypercalcaemia.
After medical management initially, a parathyroidectomy can be planned for cases of primary disease.
After surgery, protocols for calcium administration should be prepared to prevent postoperative hypocalcaemia – these typically include administration of calcitriol and calcium carbonate and an emergency protocol for IV calcium gluconate administration.
Ionised calcium levels should be monitored regularly in the acute post-operative phase (up to every 4-6 hours). These patients should be monitored closely for signs of hypocalcaemia, and an emergency pack containing IV calcium and diluent, pre-calculated doses and monitoring equipment should be available.
Nursing care of the hyperparathyroid patient involves monitoring their fluid balance carefully and providing sufficient water and toileting opportunities for a patient with severe PU/PD.
If the patient has underlying renal disease causing secondary hyperparathyroidism, additional nursing care considerations exist. These include managing nausea and pain, providing nutritional support and providing appropriate fluid therapy, with ongoing re-assessment of their fluid balance.
As you can see, even though parathyroid disorders are rare, there is a lot for us to think about when caring for these patients - particularly with regard to sample handling, monitoring, and supporting clients long term.
Have you nursed a patient with a parathyroid disorder? DM me over on Instagram and let me know!
References
Merrill, L. 2012. Small Animal Internal Medicine for Veterinary Technicians and Nurses. Iowa: Wiley-Blackwell.
Nelson, R W. and Couto, C G. Small Animal Internal Medicine. 5th ed. Missouri: Elsevier Mosby, 2014.
Stillon, J R. and Ritt, M. G. 2009. Renal Secondary Hyperparathyroidism in Dogs. Vetfolio, available from: https://www.vetfolio.com/learn/article/renal-secondary-hyperparathyroidism-in-dogs
