The Healthcare Social Graph (HSG) Score is the overall impact a Twitter profile has on healthcare social media, while SymplurRank is the impact a Twitter profile has in a specific conversation (or topic or conference, etc.).
For example, if you want to view the top influencer for hashtag #ascogu22, you would view the SymplurRank (default rank setting) in the Influencers widget.
See the example screenshot below.