I have a requirement for gathering survey feedback from patients at a medical practice. The surveys are not anonymized and I would like the participants to complete the same survey weeks/months later so we look at the data to monitor progress / responsiveness to treatment received. I would like the same participant to be able to complete the same survey (without their previously selected survey answers being viewable) - is this possible?

You can use tokens and allow the usage of tokens more than once.
That way a respondent will create a new response-record on the running survey and you can identify all responses by one respondent over time.

Please refer to the manual - "Allow multiple responses or update responses with one token" - manual.limesurvey.org/Participant_settin...onses_with_one_token