Hypoparathyroidism occurs when the body does not produce enough parathyroid hormone. Parathyroid hormone is secreted by the parathyroid glands (located in the neck adjacent to the thyroid glands) and helps keep the amount of calcium (and to a lesser extent phosphate) in the blood stable. So why is this important?

The role of calcium in keeping your dog healthy

Calcium plays a key role in many processes in the body and must be kept within a very specific range to enable these to function correctly. It is integral to strong and healthy bones, a normal heart rhythm, muscle contractions, nerve conduction, and blood clot formation. Incorrect levels of blood calcium can result in heart, nerve, or brain problems – so your dog’s ability to manage it is essential for their health.

In normal circumstances, low blood calcium stimulates the parathyroid glands to produce parathyroid hormone. This acts on: 

  • the bones to mobilise calcium and phosphate into the bloodstream, 
  • the intestine to increase vitamin D absorption (which in turn enhances calcium and phosphate intestinal absorption) 
  • the kidneys to decrease calcium and increase phosphate excretion. 

The overall effect is to increase calcium and decrease phosphate blood levels. Therefore, if there is no parathyroid hormone, there is nothing to tell the body to increase calcium absorption and decrease excretion when blood calcium is too low, and the levels stay low. 

What are the symptoms of hypoparathyroidism in Dogs?

The first symptoms to become apparent are due to calcium’s role in muscle contractions and can manifest as restlessness, muscle tremors, nervousness, weakness, wobbliness, vomiting, diarrhoea and reduced appetite. More severe cases can progress to seizures (eventually seen in up to 86% of cases). Symptoms present in chronic cases include an irregular heart rate, cataracts and weight loss. 

What are the primary causes?

There are various reasons why hypoparathyroidism occurs but thankfully these conditions are rare in dogs. The most common of these conditions (but still incredibly rare) is immune-mediated or primary hypoparathyroidism. This is when the body’s immune system malfunctions and attacks and destroys the parathyroid glands. Some breeds are more prone to developing this condition, namely Miniature Schnauzers, Toy Poodles, Labrador Retrievers, German Shepherds and Terriers. 

It can also be congenital: puppies can be born without or with poorly developed parathyroid glands that are unable to produce any hormone. 

Damage to the parathyroid glands (for example, during surgery of the neck or the neighbouring thyroid gland), an invading cancer from surrounding tissues or destruction by a virus (eg canine distemper virus – very uncommon in the UK due to successful vaccination programs) can also cause it. 

In addition, any condition causing persistently high blood calcium levels (eg kidney failure or cancer) can lead to atrophy of the gland through underuse. The calcium levels just do not drop low enough to stimulate the parathyroid gland to produce parathyroid hormone. Over time this causes the gland to waste away and unable to produce any hormone, even if the underlying condition is treated and calcium levels return to normal. 

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How is it diagnosed?

The condition is suspected on clinical signs and by ruling out other causes of weakness, seizures, wobbliness etc. An initial blood test would show low calcium and high phosphate levels. If these results come back, a specific blood test showing low levels of parathyroid hormone is then diagnostic for hypoparathyroidism.

What are the treatment options?

Primary/immune-mediated hypoparathyroidism can be treated relatively straightforwardly by firstly addressing any life-threatening symptoms (eg seizures) and correcting severely low blood calcium levels with injections of calcium directly into the bloodstream. 

This is followed by long term oral supplementation of calcium and vitamin D. In cases where the parathyroid gland has been damaged during surgery, the parathyroid gland can usually repair itself over time and therefore symptoms can resolve or only need short term treatment. 

However, treatment of other underlying causes can be more complicated eg another syndrome causing high blood calcium levels or cancer. Therefore, the prognosis depends greatly on the underlying cause.

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