Alzheimer’s disease and related dementia (ADRD) is a collection of disorders involving mental deterioration, which is often quite distressing for the individuals and those caring for them. Online social media platforms have become popular environments for people to share their ADRD caring challenges and experiences. Despite encouraging findings in the literature regarding online support for ADRD caregivers, studies to date have focused only on a single online community about ADRD, which leads to an incomplete picture of the needs of ADRD caregivers. Additionally, the large volume of data from online communities makes it challenging for both researchers and caregivers to efficiently discover discussions about ADRD care. In this paper, we focus on Reddit, an online rating and discussion platform that consists of many communities, or subreddits, and aim to analyze the topic difference regarding ADRD care between ADRD and non-ADRD subreddits. To do so, we first develop a two-stage classification framework to extract posts about ADRD care from the entire Reddit. Then, we apply structured topic modeling to investigate what has been discussed on ADRD care and how such discussions are prevalent in different types of subreddits. Our results show that non-ADRD subreddits contribute 68.5% of submissions of ADRD care, more than twice as many as ADRD subreddits. Moreover, non-ADRD subreddits are more likely to disclose legal and financial issues, negative relationships and mental health, while ADRD subreddits are more likely to talk about memory loss, sleeping and diet issues, the disease and clinical visits. Our findings suggest that research in this area should look into discussions beyond ADRD communities to gain a comprehensive understanding of ADRD caring experiences and challenges.