Most people have heard of the thyroid glands, mainly in the context of metabolism and weight in people, and perhaps dogs and cats. What they may not be so familiar with are four smaller structures called the parathyroid glands. While these might not be as famous as their larger associate (the thyroid glands), the parathyroids perform a very important function in the body. 

If your cat or dog has been diagnosed with underactive parathyroid glands, their condition is known as hypoparathyroidism.  We’ll explore this issue in more detail for you here.

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What is hypoparathyroidism?

The parathyroid glands are four small glands, two found on either side of the neck. These parathyroids are attached or embedded in the larger thyroid glands, of which there are two, one on either side of the neck. The parathyroid glands may only be approximately 2-3 mm in length, but they perform a big job. They help to regulate calcium levels in the blood by producing parathyroid hormone. Calcium is extremely important in the body as it helps to control the way that all muscles and organs (including the brain, kidneys and bowels) function. It is particularly essential for muscle contraction and stabilises nerve cell membranes.

In cases of hypoparathyroidism, these glands are not producing enough parathyroid hormone, and calcium levels around the body start to fall. If levels of calcium are not appropriately maintained and controlled, then the animal can start to become unwell. They can show signs of increased excitability in their central nervous system and muscles, leading to twitches, tremors and abnormal movements. 

It is worth noting that this condition is different to hyperparathyroidism which is where parathyroid levels are high, and calcium levels become too elevated. 

What causes hypoparathyroidism in dogs and cats?

This condition is uncommon in dogs, and even rarer in cats, so it is certainly not something diagnosed every day in practice. 

Hypoparathyroidism most commonly occurs due to one of the following reasons –

  • Primary/idiopathic – we often don’t know why hypoparathyroidism occurs, but it is likely in many cases to be immune-mediated (the body’s own self destroying the parathyroid tissue)
  • Trauma, often from surgery in the neck – for example in cats that have had their thyroid glands removed due to hyperthyroidism (a tumour on the thyroid gland). This is certainly the most common cause of hypoparathyroidism in cats and is a known complication of the surgery. In many cases, however, it is transient and will improve. Other types of trauma, such as bite injuries, can also cause parathyroid issues. 
  • Congenital hypoplasia or aplasia – underdeveloped or non-existent parathyroid glands, which the animal will have had since birth  
  • Animals that have had elevated calcium levels – In conditions like kidney failure or cancer, high blood calcium levels can occur which causes the parathyroid to become redundant. It becomes atrophied (or ‘wasted’) when it is not being used for an extended period. Even if the issue causing the elevation in calcium levels is resolved (and calcium in the body lowers), the hypoparathyroids may not be able to produce their hormones anymore.    
  • Severe hypomagnesia – a severe deficiency in magnesium which could be dietary or caused by other illness  
  • End organ resistance – the target organs are not responding to the parathyroid hormone that has been      excreted
  • Distemper virus in dogs – Distemper virus particles in some affected dogs can lead to issues with calcium control

Are there any symptoms of hypoparathyroidism in pets?

Affected animals will usually show the following symptoms, but these may be intermittent in nature in some cases –

  • Restlessness
  • Panting
  • Decreased appetite 
  • Weakness
  • Muscle tremors, twitches or cramping
  • Rigid muscles or a stiffened gait when they walk
  • Seizures 
  • Ataxia (uncoordinated movement)
  • Cataracts developing in the eyes

How is hypoparathyroidism diagnosed in dogs and cats?

Your vet will start by examining your pet and reviewing their notes for any relevant history of recent surgery (especially around the neck area). Your vet will assess your pet’s movements to look for abnormalities, as well as give them a nose-to-tail examination. 

It may be possible to see secondary issues from their parathyroid problems, such as cataract formation in the eyes, an abnormal heart rate or rhythm when listening to their chest and changes in your pet’s muscle tone and rigidity. Sometimes, however, no external abnormalities are detected at all. It may depend on what point in disease progression your pet is at.

Blood tests are usually advised next. Your vet will be interested in your pet’s calcium levels in particular, but they will also want to check their organ function, looking at their kidney and liver parameters. Phosphorus levels might also be increased in affected animals. They may also check your pet’s haematology (red and white blood cells) to rule out other disease processes. 

It is often necessary to do more specific blood tests to reach a definitive diagnosis. This may include an ionised calcium blood test which looks at biologically active calcium in the blood and is preferred to looking at your pet’s total calcium alone. Your vet will also suggest a blood test that measures your pet’s parathyroid hormone levels (PTH). If both PTH and calcium levels are constantly low, then a diagnosis of hypoparathyroidism is made. 

How is hypoparathyroidism treated?

Treatment for affected animals is aimed at increasing calcium levels in the body. This may need to be done via hospitalisation and injections initially, to get levels back up to normal. Here your vet can also monitor and treat your pet for other issues such as seizure activity. This can then be followed orally by feeding diets high in calcium and low in phosphorus or administering calcium supplements.

Vitamin D supplements are also recommended which also help to further increase the calcium levels in the blood. This treatment regime can offer a good prognosis in many cases. 

In some pets, this treatment may only need to be given short term. For example, if the parathyroid glands have sustained some trauma during surgery, they can recover their function again over time. If necessary, long-term treatment can help pets with ongoing calcium issues. Your vet may advise monitoring blood tests to ensure that the level of supplementation is effective. 

However other cases can be trickier to treat, for example in patients with other underlying disease processes that are causing secondary hypoparathyroidism – like cancer, severe bowel disease or kidney failure. The primary disease process will greatly affect their long-term prognosis.

Final thoughts

Hypoparathyroidism (underactive parathyroid glands) is an uncommon diagnosis in both cats and dogs, with several possible underlying causes. The prognosis will depend on the underlying reason why the animal has developed the condition. If your pet has already been diagnosed with hypoparathyroidism then you will need to speak to your vet for more information on what the most likely cause is and also what your pet’s longer-term outlook is. 

If you have any concerns about your pet, or if they are showing symptoms like the ones listed in this blog then ring your vet to make an appointment.  

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