Newfoundland Immune-Mediated Thyroiditis: The Silent Phase Before the Disease

The immune system's job is to recognise what belongs to the body and leave it alone. In autoimmune disease that recognition fails, and in immune-mediated thyroiditis the failure is directed at the thyroid gland. Immune cells infiltrate the gland and progressively destroy hormone-producing tissue.

The thyroid has considerable spare capacity, which is both a blessing and the reason this is so hard to catch. A substantial proportion of the gland can be lost before circulating hormone levels drop below the normal range, because the surviving tissue simply works harder. During that period the dog has an active disease process and a normal blood test.

What antibody testing does is look for the attack rather than for the consequence. Detecting antibodies directed against thyroid proteins indicates that the immune process is under way, regardless of whether hormone output has yet fallen. A dog can therefore be antibody positive and hormonally normal, which is exactly the confusing result many owners receive.

That result is not a diagnosis of hypothyroidism and it does not mean treatment should start. It means the dog is on a trajectory that deserves monitoring, and, importantly, that this is information a breeding programme should take seriously.

Two tests answering two different questions produce four possible combinations, and each one implies something different. This is why the result should be explained by a veterinarian rather than read off a page.

For a pet owner whose dog feels well, an antibody result changes very little in the short term. It adds a monitoring schedule and a reason to pay attention to weight, coat and energy, but it does not change today's care.

For a breeder the calculation is completely different. The predisposition to autoimmune thyroid disease is inherited, and a dog that is antibody positive at two years old is likely to develop clinical disease later and to pass the tendency to its offspring. Testing before breeding decisions are made is therefore a way of removing a heritable problem from a line rather than discovering it one generation later.

Because antibody status can appear at different ages, breeders who take this seriously typically retest over time rather than testing once. A clear result at fourteen months is worth having and is not permanent.

There is a broader point here for anyone buying a puppy. In a breed whose documented health concerns already include hip dysplasia, subaortic stenosis, dilated cardiomyopathy, cystinuria and bloat, thyroid screening is an optional extra rather than a core requirement. It is a marker of how thorough a breeder is, more than a box that must be ticked.