Changes

== Introduction ==

== Introduction ==

Hypothyroidism is a common endocrine disorder in dogs. Approximately 90% of cases are due to acquired, primary disease (lymphocytic thyroiditis or idiopathic thyroid atrophy). Middle-aged dogs are most commonly affected and Golden Retrievers, setters, Doberman Pinschers, Great Danes, Schnauzers, spaniel breeds and terriers appear predisposed. The clinical findings include skin changes (alopecia, seborrhoea, pyoderma, puppy coat, hyperpigmentation, hyperkeratosis, myxoedema and slow hair growth), lethargy, obesity, intolerance to cold and reproductive abnormalities. When thyroid disease is suspected routine haematology and biochemistry screens are recommended to eliminate other conditions which may produce similar clinical signs. Nonspecific laboratory findings in hypothyroid dogs include hypercholesterolaemia, mild non-regenerative anaemia, high serum alkaline phosphatase activity and high serum creatinine kinase activity. None of these changes are pathognomonic. Skin biopsy may reveal non-specific histological findings for example, orthokeratotic hyperkeratosis, epidermal atrophy and epidermal melanosis or findings suggestive of hypothyroidism for example, vacuolated and/or hypertrophied arrector pili muscles, thickened dermis and increased dermal mucin. There are a great many factors affecting thyroid hormone levels in dogs and confirmation of hypothyroidism can be difficult. It is essential that a thorough clinical examination is performed and history taken prior to any diagnostic testing. The following factors are also very important to consider when carrying out thyroid function tests:

Hypothyroidism is a common endocrine disorder in dogs. Approximately 90% of cases are due to acquired, primary disease (lymphocytic thyroiditis or idiopathic thyroid atrophy). Middle-aged dogs are most commonly affected and Golden Retrievers, setters, Doberman Pinschers, Great Danes, Schnauzers, spaniel breeds and terriers appear predisposed. The clinical findings include skin changes (alopecia, seborrhoea, pyoderma, puppy coat, hyperpigmentation, hyperkeratosis, myxoedema and slow hair growth), lethargy, obesity, intolerance to cold and reproductive abnormalities. When thyroid disease is suspected routine haematology and biochemistry screens are recommended to eliminate other conditions which may produce similar clinical signs. Nonspecific laboratory findings in hypothyroid dogs include hypercholesterolaemia, mild non-regenerative anaemia, high serum alkaline phosphatase activity and high serum creatinine kinase activity. None of these changes are pathognomonic. Skin biopsy may reveal non-specific histological findings for example, orthokeratotic hyperkeratosis, epidermal atrophy and epidermal melanosis or findings suggestive of hypothyroidism for example, vacuolated and/or hypertrophied arrector pili muscles, thickened dermis and increased dermal mucin. There are a great many factors affecting thyroid hormone levels in dogs and confirmation of hypothyroidism can be difficult. It is essential that a thorough clinical examination is performed and history taken prior to any diagnostic testing. The following factors are also very important to consider when carrying out thyroid function tests:

* Take 2ml of clotted or heparinised blood

* Take 2ml of clotted or heparinised blood

* Inject TRH slowly i/v over 1 minute using the dose rates below. Please note: TRH can cause mild side effects such as defecation, salivation, tachypnoea. If these cause a problem, atropine is an effective antidote. Thyrotropin Releasing Hormone is available on prescription as TRH Cambridge Laboratories*.

* Inject TRH slowly i/v over 1 minute using the dose rates below. Please note: TRH can cause mild side effects such as defecation, salivation, tachypnoea. If these cause a problem, atropine is an effective antidote. Thyrotropin Releasing Hormone is available on prescription as TRH Cambridge Laboratories*.

 

1-5kg 100μg TRH

 

|1-5kg  

5-30kg 200μg TRH

|100μg TRH

 

>30kg 300μg TRH

|5-30kg

|200μg TRH

|>30kg

|300μg TRH

* Take a second 2ml of clotted or heparinised blood 4 hours after TRH injection

* Take a second 2ml of clotted or heparinised blood 4 hours after TRH injection

* If the pre-stimulation T4 is >25nmol/l, regardless of the post-stimulation concentration, the dog is normal

* If the pre-stimulation T4 is >25nmol/l, regardless of the post-stimulation concentration, the dog is normal

* With a pre-stimulation T4 <25nmol/l, the post-stimulation values can be interpreted as follows:

* With a pre-stimulation T4 <25nmol/l, the post-stimulation values can be interpreted as follows:

 

0-20nmol/l Hypothyroid or sick euthyroid

 

|0-20nmol/l  

20-30nmol/l Status equivocal

|Hypothyroid or sick euthyroid

 

>30nmol/l Normal

|20-30nmol/l

|Status equivocal

|>30nmol/l

|Normal

* Dogs with equivocal values should be retested after 1 month

* Dogs with equivocal values should be retested after 1 month

== Authors & References ==

== Authors & References ==

[[NationWide Laboratories]]

[[NationWide Laboratories]]