Endocrinology (hypothyroidism) Flashcards
Hypothyroidism
Describe the epidemiology and the cause of congenital hypothyroidism
Naturally occurring hypothyroidism is an extremely uncommon disorder in cats
Most cases appear to be primary and are seen in kittens with an inborn error of metabolism
Although an inherited basis has been documented in some, many cases are observed as sporadic abnormalities
What are the clinical signs of hypothyroidism
Disproportionate dwarfism (stunted growth, short legs, broad body and skull)
Delayed or incomplete eruption of permanent teeth
Mental dullness/retardation
Constipation
+/- Palpable goiter
Delayed physeal closure
Retention of undercoat and loss of primary hairs giving a short, soft coat
How can you make a diagnosis of hypothyroidism
The TSH stimulation test is the preferred diagnostic test as this causes a greater proportionate rise in T4 and T3 levels in healthy cats
A TSH dose of 1 UI/cat IV stimulates maximum thyroid hormone concentrations 6-8 hours later with post-TSH T4 levels typically 2-4 times basal levels
Hypothyroid cats would be expected to have low basal T4 and fT4 levels which do not appreciably increase after TSH stimulation
The finding of an elevated TSH concentration is considered to be the most sensitive of the currently available tests for detection of iatrogenic or spontaneous hypothyroidism
How would you treat a cat with hypothyroidism and what is the prognosis
Therapy is with thyroid hormone supplementation (10-20 µg/kg daily)
The prognosis is variable
The earlier the condition is diagnosed the better the prognosis is
Explain the causes of adult-onset hypothyroidism
This is a sporadic natural disease in the cat
Iatrogenic hypothyroidism is seen with some frequency following radioiodine therapy or over-zealous administration of anti-thyroid drugs
- It is especially important that this possibility is investigated in azotemic cats
What are the clinical signs of hypothyroidism
Lethargy/apathy
Weight gain/obesity
Hypothermia/cold intolerance
Myxedema
Seborrhea sicca
Alopecia of the pinnae and/or mild alopecia of the general haircoat
Hyperkeratosis
PUPD with mild-moderate evidence of renal dysfunction (may be reversible with treatment)
Poor appetite
Bradycardia
Palpable goiter (common)
How can you make a diagnosis of feline hypothyroidism
The finding of a sub-normal TT4 is often due to “sick euthyroidism”
However, the clinician should be alerted to the possibility of acquired hypothyroidism if the cat is not otherwise unwell or has previously undergone radioiodine treatment
The finding of an elevated TSH is diagnostic
