HYPOTHYROIDISM IN DOGS AND CATS

Question 1

DEFINE

Hypothyroidism

Answer 1

Deficit of thyroid hormone due to the affection of any one of the hypothalamo pituitary thyroid axis.

Question 2

Classification of hypothyroidism with the site of affection.

Answer 2

• Primary HypoT - Thyroid gland T4,T3
• Secondary HypoT - Pituitary gland Thyrotropine - TSH
• Tertiary HypoT - Hypothalamus - TRH
• Congenital HypoT - Thyroid gland dysgenesis(aplasia, hypoplasia, ectasia)

Question 3

Clinical signs of HypoT in dogs.

Answer 3

• Decreased metabolic rate
• Lethargy
• Weight gain
• Mental dullness
• Cold intolerance
• Dermatologic signs
• Reproductive signs
• Neurologic signs
• Ocular
• Cardiovascular
• GI
• Hematologic

Question 4

Dermatologic signs in HypoT

Answer 4

• Bilateral symetric non pruritic trunkal alopecia, seborrhoea, pyoderma, dry brittle rough easily epilatin hair, hyperpigmentation,hyperkeratosis,dry scaly hair,ceruminous otitis,comedone formation
• Rat tailed
• Myxedema

Normochromic normocytic regenerative anemia,
hypertriglyceridemia and hypercholesterolemia

Question 5

Myxedema

Answer 5

• In severe cases of hypothyroidism, acidic and neutral mucopolysaccharides may accumulate in the dermis and bind water, causing the skin to thicken. Referred to as** myxedema,** this condition causes the skin to thicken predominantly in the forehead and face of dogs, resulting in rounding of the temporal region of the forehead, puffiness and thickening of the facial skin folds, and drooping of the upper eyelids.
  * Tragic facial expression

Question 6

Cretinism

Answer 6

Hypothyroidism in puppies is termed cretinism. Retarded growth and impaired mental development are the hallmarks of cretinism and clinical signs present only by 1-3 months.
Disproportionate dwarfism
Short, broad skull
Shortened mandible
Enlarged cranium
Shortened limbs
Kyphosis
Mental dullness
Constipation
Inappetence
Gait abnormalities
Delayed dental eruption
Alopecia
“Persistent Puppy haircoat”
Dry hair
Thick skin
Lethargy
Dyspnea
Goiter

Question 7

Diagnosis

Answer 7

• Clinical signs
• History
• Biochemical panel
• Hematology
• Ultrasound
• TSH Stimulation test
• TRH Stimulation Test
• Therapeutic trial (20 microgram/kg Q12hrs)
• Thyroid T4 estimation
• ELISA estimating Antithyroglobulin Antibodies

Serum T4, fT4,TSH — RIA, Chemiluminescence assay, ELISA, Mod Equi Dial

fT4 > 1.5ng/dl euthyroidism
fT4 < 0.5-0.8ng/dL hypothyroidism
TSH Upper Limit = 0.6ng/dL

Question 8

Treatment of hypothyroidism

Answer 8

• Sodium Levothyroxine - Synthetic T4 @ 0.01-0.02 mg/Kg Q12 hrs for a minimum of 6-8 weeks
• By 1 week improvement in mental alertness and activity
• By months improvement in hair growth and hyperpigmentation
• 4-8 week recheck T4 and TSH 4-6hrs after taking levothyroxine