Veterinary Information:
Hypothyroidism in Dogs

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Symptoms:
Hypothyroidism (hypoT4) signs can be vague which makes it a frequently misdiagnosed disease. A decreased metabolic rate combined with dermatological and haircoat problems are important first indicators of hypoT4.

-Lethargy
-Obesity (40%) (Overnutrition is a far more common cause of obesity!)
-Dermatologic changes (60%)*
-Painful gait
-Sleeping on warm spots
-Decreased body temperature
-Female and male infertility**
-Myxedema***
-Neurological dysfunction****
-Ocular abnormalities*****
-Bradycardia
-Gastrointestinal disorders
-Weak peripheral femoral pulse and ictus cordis

-Coagulopathies (a decreased vWF plasma level can be found)
-Low voltage ECG, inverted T-waves
-Low Ht (mild non-regenerative anemia) (30%)
-Fasting hypercholesterolemia (75%)
-Increased CK (due to a myositis)

* Dermatological changes: dry skin, poor haircoat quality and loss of colour, alopecia, pyoderma, seborrhoea, hyperkeratosis, hyperpigmentation, increased bruising, myxoedema, poor wound healing. There is also an increased risk of demodicosis and malassezia infections. Alopecia is mostly bilateral symmetric and first visible at the lateral trunk, ventral thorax and tail. A failing regrowth of hair after clipping can also occur.
**Female infertility: prolonged interestrous interval, silent heat, spontaneous abortions.
Male infertility: decreased libido, testicular atrophy, hypospermia.
***Myxedema is an uncommon symptom of canine hypoT4. There is a thickening of the skin, mainly of the eyelids, cheeks and forehead. This is due to a disposition of hyaluronic acid in the dermis.
****Peripheral and Central Nervous System can be affected by hypoT4. Signs: Exercise intolerance, weakness, ataxia, paresis/paralysis, decreased spinal reflexes. Cranial nerves may also be affected: tilted head (vestibulocochlear nerve), facialis paralysis. Myasthenia Gravis has been reported to occur in association with hypoT4. (Both conditions are immune-mediated). In MG a mega-oesophagus and laryngeal paralysis with altered vocalisation are commonly seen.
*****Ocular abnormalities: corneal lipidosis, corneal ulcers, uveitis, KCS, secondary glaucoma and retinal detachment.

Canine hypothyroidism can be combined with other immune-mediated conditions: Hypoadrenocortisism, Myasthenia Gravis, Diabetis Mellitis.
Note: HypoT4 can also cause insuline resistence.

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