And, as it turned out, that scan was the wrong kind to show signs of frontotemporal dementia. Not long ago, I spoke with the neurologist Brad Dickerson, Katie’s boss, about why frontotemporal dementia is difficult to diagnose. But his expertise lies in frontotemporal dementia, a fatal disease that progresses over time, as short as three years or as long as 12. One cause of diagnostic confusion is that the early symptoms of Alzheimer’s dementia – the most common cause of dementia in older adults – are different from frontotemporal dementia. Jill recounts the darker side of frontotemporal dementia, one that can subject a family or caregiver to intolerable threats.