A dog with thinning skin is more likely to have **Cushing's disease (hyperadrenocorticism)**.
Why?
Cushing's Disease causes catabolic effects on collagen, leading to:
* Thinning of the skin (atrophy).
* Increased susceptibility to bruising.
* Poor wound healing.
In contrast, **hypothyroidism** is associated with **thickened skin**, sometimes called "myxedema," due to mucopolysaccharide accumulation in the dermis. Hypothyroidism more commonly causes **alopecia, thinning hair and a dull, dry coat** but not thinning skin.