Thyroid Disorders Flashcards
What are the clinical signs of hyperthyroidism?
Older cats Weight loss with variable appetite PD Hyperactive/lethargy Cardiac changes (Tachy +/- gallop rhythm and systolic murmurs) Thyroid nodules
Explain why hyperthyroidism causes cardiovascular disease…
Increased catecholamine sensitivity so tendency to develop tachycardia and tachydysrhythmias alongside a diastolic gallop rhythm due to impaired ventricular relaxation. Tachypnea and panting may also be present and there is decreased systemic vascular resistance.
How does hyperthyroidism cause heart failure?
Increase in T3 leads to increased tissue thermogenesis, increased cardiac inotropy and chronotrophy and decreased systemic vascular resistance. Decreased systemic vascular resistance leads to a decreased in effective arterial filling volume and thus an increase in renal sodium reabsorption. This, along with the increased in cardiac inotropy and chronotrophy leads to decreased cardiac output (volume overload).
What does hypertension cause in cats?
Retinal haemorrhage and detachment.
What is the linked between hyperthyroidism and hypertension?
Hyperthyroid cats tend to be more stressier and as they are more sensitive to catecholamines you get a bigger response to small stresses.
How can treating hyperthyroidism lead to hypertension?
Hyperthyroidism decreases vascular resistance so if treated vascular resistance will increase.
What is seen on haematology and biochemistry of a hyperthyroid cat?
Elevated ALT and ALP Elevated bile acids Stress leukogram Physiological neutrophillia Urea higher than creatinine
How do you diagnose hyperthyroidism?
Basal total T4
Basal free T4
T3 suppresion test
Scintigraphy
How does hyperthyroidism affect GFR?
Increases GFR, hyperfiltration leads to glomerular sclerosis and eventually decreases GFR
How can treatment of hyperthyroidism affect renal function?
Reduces GFR so the animal may become azotaemic.
How would you treat hyperthyroidism in the cat?
Carbimazole
Methimazole
Unilateral or bilateral thyroidectomy
Thyroid irradiation
Explain how carbimazole/methimzaole treats hyperthyroidism..
Blocks TH production
Describe medical therapy guidelines for a hyperthyroid patient…
Carimazole at 10-15mg/day or methimazole at 2.5-5mg/day induction which lasts for 3 weeks.
What are the adverse effects of medical treatment in a hyperthyroid patient?
GI signs: V/D, inappetence
Depression, lethargy
Facial pruritis
Anaemia
What are the possible complications of thyroidectomies?
Hypocal
Recurrence of hyperthyroidism
What dietary changes can be introduced to a hyperthyroid cat?
Diet with minimal iodine content e.g. hills y/d
What species are associated with hypothyroidism? What causes it?
Dogs - congenital via enzyme deficiency of acquired by immune-mediated destruction of thyroid tissue.
What are the clinical signs of hypothyroidism?
Lethargy Overweight Exercise intolerant Alopecia, hyperpigmentation, thickened skin Infertility
What would you expect on clinical pathology in a hypothyroid patient?
Mild non-regenerative anaemia
+/- elevated cholestero
+/- elevated CK
+/- proteinuria
What is a DDx for hypothyroidism in young dogs? How are they differentiated and which breeds are predisposed to both?
Pituitary dwarfism.
Hypothyroidism will have abnormal calcification of long bones on radiographs
GSD predisposed.
How is hypothyroidism diagnosed?
Combination of low basal total T4 and normal/elevated basal TSH.
How is hypothyroidism treated?
Thyroxine tablets once daily
