Spasm by Robin Cook

 When NYC Chief Medical Examiner Laurie and her husband (forensic pathologist) Jack Stapleton find themselves with some unexpected free time, they head up to bucolic Essex Falls, to visit Bob Nielsen, an old medical school pal of Jack's. Dr Bob is both the only physician and the coroner for the small town and he welcomes Jack and Laurie's expertise on an autopsy--then the body disappears. Dr Bob also mentions that there has been a rash of cases recently of people suddenly developing Alzheimer's-like symptoms then dying soon after. That sets off Jack's spidey senses and he wonders if the missing body and the seeming epidemic are related. It's a compelling and fairly scary tale because it's easy to imagine something like this really happening.