Hypothyroidism is caused by an inactive thyroid, often following the destruction of the thyroid gland, usually by the patient’s own immune system. Genetics play a role in the condition, which is more common in certain breeds (click here for breeds).
SEVERITY: Chronic. Requires ongoing medication.
Visible symptoms usually develop during middle age, from about 2 to 6 years of age. Signs are quite variable and depend, in part, on the age of the dog. In the adult, the most consistent signs are related to changes in activity and mental status. The most common signs seen are those related to skin and hair coat.
Some or all of the following signs may be seen:
- lethargy, mental dullness, inactivity, weight gain, cold intolerance
- hair loss, ‘rat tail,’ dry brittle hair coat, coat that is slow to grow, scales and dandruff, hyperpigmentation (where skin changes to black colour), skin infections, ear infections.
- reproductive abnormalities
- seizures, weakness, difficulty maintaining balance
- eye problems
- bradycardia (slow heart rate), cardiac problems
- diarrhoea, constipation
- anaemia, bleeding disorders.
Fasting blood tests are required for diagnosis. Generally we recommend a full blood profile at the same time to assess general health and to monitor for changes that are secondary to the hypothyroidism itself.
Hypothyroidism is treated by supplementing the thyroid gland with a synthetic hormone. An initial dose is calculated based on the patient’s bodyweight and tablets are given twice daily. Because of the variability in response to the treatment in individual dogs this initial dosage and frequency may require adjusting before a complete clinical response is observed.
After a month on a set dose blood tests are repeated to check for blood levels, measuring hormone levels just before tablets are given then again several hours after to measure the lowest and highest levels achieved in the bloodstream.
An increase in mental alertness, activity and appetite are the initial signs of improvement and are usually seen in the first week. Noticeable changes in the skin and some hair improvement should be seen in the first month. However, the cost often looks worse before it looks better as the old hair is shed in large quantities. It may take several months before complete regrowth occurs.
Once a dose is decided on and the patient stable blood tests are repeated every 6-12 months as dose requirements can change over time. The prognosis for dogs suffering hypothyroidism is excellent.