A 54-year-old woman presents with vaginal itching and thin vaginal mucosa post-menopause. What is the most likely cause?

Atrophic vaginitis is the most likely cause of vaginal itching and thin vaginal mucosa in a post-menopausal woman. This condition arises due to the decreased levels of estrogen that occur after menopause. Estrogen plays a crucial role in maintaining the health and thickness of vaginal tissues. When estrogen levels drop, the vaginal mucosa becomes thinner and more fragile, leading to symptoms such as dryness, itching, and discomfort.

The thinning of the vaginal walls associated with atrophic vaginitis can also make the area more susceptible to irritation and inflammation, reinforcing the cycle of discomfort. This condition is a common, yet often under-discussed aspect of post-menopausal women's health, highlighting the importance of estrogen in maintaining vaginal health and function.

In contrast, lichen sclerosis usually presents with more severe symptoms and specific lesions on the vulva, not typically just thinning of the mucosa. Contact dermatitis is generally associated with specific irritants or allergens causing inflammation rather than the systemic changes seen in menopause. Candidiasis is characterized by thick, curd-like vaginal discharge, which is not consistent with the description of thin mucosa and itching. Thus, atrophic vaginitis is the most appropriate diagnosis given the context provided.