Hypothyroidism

By Jonathan Amos (B. Vet. Med.)

The thyroid is one of the dog's hormone producing glands.  Hormones 
are the messenger substances which circulate in the body regulating all 
the various functions.


Typically one hormone can affect many different organs and body 
symptoms.  Hypothyroidism is the commonest endocrine disorder in the 
dog.  Dachshunds are among the breeds affected, typically more in 
standards than miniatures.


Some dogs can be born with underactive thyroids but the vast majority 
seem to develop it in later life, usually between 5 and 9 years old.


CHANGES IN THE DOG

1) SKIN CHANGES

Typically there is a bilateral symmetrical (i.e. roughly the same on either 
side of the dog) area of hair loss affecting the flanks.  This is generally 
not itchy.  Eventually the underlying skin becomes black and thickened.  
The skin around the face often becomes folded and puffy, giving the dog 
a worried or anxious look.  Hypothyroid dogs tend to feel the cold and 
actively seek out sources of heat.  (This is normal in about 99.9% of 
Dachshunds anyway!!)  The skin itself feels cold to the touch.


One of the first signs of hypothyroidism is that the coat is very slow to 
grow back after clipping or stripping.


2) CHANGES IN THE REPRODUCTIVE SYSTEM

In bitches, seasons may become irregular and/or stop altogether.  


Dogs may show a lack of libido coupled with a decrease in size of the 
testicles.  (This may or may not be readily apparent as not many dog 
owners keep a record of the size of their dog's testicles!)


3) OTHER SYMPTOMS

In more severe cases the heart muscle may be affected, the heart rate 
also slows leading to episodes of collapse.


The dog generally tends to put on weight and become obese very easily, 
thus aggravating the already stressed heart.




DIAGNOSIS

This is by blood test to check on the level of thyroid hormones.  The level 
of cholesterol in the blood is also checked as this rises sharply in affected 
dogs.


Small sections (biopsies) of skin may also help in diagnosis.


TREATMENT

This is simply by giving synthetic thyroid hormone by mouth, usually once 
daily.  Improvement is generally fairly slow.  The first sign to go is the 
lethargy, then gradually the weight goes down.  Changes in the coat may 
not occur for 2 - 3 months.  Anoestrus bitches may quickly come back 
into season.  Because of the length of time involved it is important not to 
give up too soon and think the treatment isn't working.  Thereafter 
treatment is for life and is usually (except in rare cases of thyroid cancer) 
very successful.


JONATHAN AMOS B. Vet. Med.

January 1998

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