Frontotemporal dementia can present with preserved memory but significant changes in language or behavior, and may be misdiagnosed as bipolar disorder.

“frontotemporal dementia is one where people often present with relatively preserved memory but significant changes in language or behavior and usually you know within a minute i can diagnose them because the loved one will say well his memory is not so bad but and it's either you know he can't really talk anymore which can also happen in alzheimer's fairly early in some people or you know i'm embarrassed to take him to church because he he'll get up and take the microphone from the pastor and you know you almost know okay this is ftd. those are often the people that erroneously get diagnosed with bipolar illness because of these sudden and really profound behavior changes problems with judgment where they get labeled as being manic because they're spending lots of money or they're you know responding to every publisher's clearinghouse thing that comes in the mail”