I'm sorry, I overlooked you had put Kartel's breed before.
Typically, hypothyroidism in dogs is secondary to immune-mediated destruction of the thyroid gland (the body attacks the thyroid gland). I have not heard of trauma causing an issue before, but anything is possible. If a dog's thyroid levels test low, we typically start them on thyroid hormone supplementation. There are a bunch of different brands on the market. Once we get them started for a few weeks, we retest to make sure they are now back in the normal range. If they are not, we need to increase the dose. We then typically monitor the thyroid level at least yearly once it's back in the normal range, as sometimes we do need to make dosing adjustments. Typically, it may take several months before their skin will slowly start to improve.
Doing the limited ingredient diet certainly won't hurt.
I'm going to send you a link to a good website that has some great information about hypothyroidism in dogs.
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