Exam 5: Canine Hypothyroidism

generally describe the major thyrid hormones

• T3 and T4, 99% are protein bound, free form is active

• active in most cells in the body except brain, lungs, spleen, uterus, testes

• increases metabolism

• binds to DNA, regulates genes that code for regulatory proteins

what are the physiologic effects of thyroid hormones

• increase metabolic rate

• catabolic effects

• cardiact

• stimulate erythropoiesis

• regylate cholesterole

• normal growth of neurologic/skeletal system → mental alertness, peripheral nerves in adults

generally describe acquired hypothydroidism

• primary typically from lymphocutic destruction or atrophy

• inlammatory infiltration, replacement with fibrous connective tissue

• atrophy= replacement by adipose and connective tissue

what signalments are associated with hypothydroidism

• a dog problem

• goldens

• dobies

• great dane

• english and irish setters

• shetland sheepdog

• beagle

• borzoi

• toy fox terrier

  • middle aged, either gender

what are the general metabolic clinical signs of hypothydroidism

• low metabolic rate with insidious onset

• lethargy

• weight gain

• heat seeking

• mental dullness

what are the dermatologic clinical signs of hypothyroidism

• symmetrical alopecia → failure of hair to grow back

• seborrhea

• change in hair quality to be dry, brittle, puppy-like coat

• hyperpigmentation

• dry, scaling skin

• superficial pyoderma

• otitis

• myxedema

what are the neurologic clinical signs of hypothyroidism

• peripheral = weakness, exercise intolerace, quadriparesis, ataxia, CP deficits, decreased spinal reflexes

• cranial nerves= facial nerve paralysis, vesibular disease

• cerebral dysfunction rare, seizures, vestibular disease

what are the cardiovascular signs of hypothyroidism

• bradycardia

• weak apex beat

what are other possible clinical signs of hypothyroidism

• reproductive dysfunctio such as low birth weight, periparturient mortality

• galactorrhea secondary to hyperprolactinemia

• megaesophagus

• laryngeal paralysis

what is sensitivity

• measures the dogs that are correctly identified as having the disease

• SnOUT

  • trust the negative

what is specificity

measures the amount of animals correctly identified as negative

SpIN

trust the positive

what are the major steps of diagnosing hypothyroidism

• CLINICAL SIGNS
  CLINICAL SIGNS
  CLINICAL SIGNS

• minimum database

• thyroid specific testing

how may a minimum database present for hypothyroidism

• to rule out or identifiy other conditions

• normocytic, normochromic, nonregenerative anemia

• fasting hypertriglyceridemia

• fasting hypercholesterolemia

• mild increase in hepatic enzymes

what are the thyroid specific diagnostic tests

• total T4

• free T4

• TSH

• tT3 and fT3, antibodies, therapeutic trial, stim test

how is total T4 used for hypothydroid testing

• good screening but not conformatory

• highly sensitive

• moderately specific, false positive common due to fluctuations in normal dog due to breed, age, time of day, temp, drugs, other illnesses

what is sick euthyroid syndrome

• effect of concurrent illness on thyroid hormone levels
  -decreased tT4, normal to decreased fT4, normal TSH

• normal physiologic response

• caused by decreased thyroid response to TSH and deactivation of T4

• does not need supplementation

how is free T4 used for diagnosing hypothyroidism

• active form

• more specific than tT4 only if by equilibrium dialysis

• less effected by Euthyroid Sick Syndrome

  • more expensive

  • confirmation

how is TSH used in diagnosing hypothydroidism

• screening test in people

• only high in 70% of hypothyroid dogs
  -drugs/illnesses
  -fluctuations
  -pititary desensitization

what drugs affect thyroid testing

• glucocorticoids

• phenobarbital

• TMS

how is T3 and fT3 used for hypothyroid

DO NOT USE

how are antibodies used for hypothyroid

found in 50% of hypothyroid dog

can interfere with tT4 measurement

increase suspicion but not diagnostic

what are additional testing options for hypothyroidism

• TSH stimulating test is gold standard but

• TRh stimulation - equivocal results

• ultrasound is insensitive and operator dependent

how is a threapeutic trial rum

• 20mcg/kg BID, evaluate 4-8 weeks later

• eval weight loss, pyoderma, neuro

• if response, discontinue to determine if related