Too often, doctors and caregivers see symptoms of dementia as permanent when the problem may be a simple infection Among the myriad ways my kids have it better than me: As a child, I had only two grandparents, one of whom died when I was still very young. But my kids, at least the older two, were born with a full complement of grandmas and grandpas, plus a great-grandmother, and while the ranks of grandparents have thinned somewhat in recent years, that 98-year-old “Nanny,” my wife’s grandmother, endures. In fact, Nanny continues to live on her own, in an Upper Manhattan apartment, with the support of her walker, a daytime home-care aide, and a delightful pet cat. She manages her finances and keeps up with her large extended family, limited in conversation only by her somewhat impaired hearing. So it was a surprise to many of us when she recently started to show fairly sudden and pronounced signs of dementia, characterized by mood swings, a far less sharp conversational tone, and paranoia, especially about her finances. Still, given her age, many of those around her imagined that this was it, that she had finally succumbed to dementia and would face declining faculties for the rest of her life. We were wrong. After a few weeks, Nanny was taken to her doctor to find out what the cause of her dementia might be. As it turned out, she was not suffering from Alzheimer’s disease or, in fact, any permanent dementia-causing syndrome. She had a simple urinary-tract infection, which was treated with antibiotics, restoring her previous sharpness. I should have been able to come up with this diagnosis. My late mother long lived with, and eventually died from complications of, vascular...