Mild cognitive impairment (MCI), a transitional stage between normal cognition and Alzheimer's disease, exists in two different forms, according to a study published today by researchers from the University of Pittsburgh School of Medicine and the University of California, Los Angeles in the Archives of Neurology.
Using a new imaging procedure that creates 3-D maps of the brain, researchers determined specific areas that had degenerated in people with MCI. Depending on the person's symptoms, more tissue was lost in the hippocampus, a brain area critical for memory and one of the earliest to change in Alzheimer's disease, indicating two different paths of progression to Alzheimer's disease. The finding could lead to better diagnosis and treatment of patients with MCI, perhaps delaying or preventing the onset of dementia.
MCI is categorized into two sub-types – currently distinguished based solely on symptoms. Those with MCI, amnesic subtype (MCI-A) have memory impairments only, while those with MCI, multiple cognitive domain subtype (MCI-MCD) have other types of mild impairments, such as in judgment or language, but also have either mild or no memory loss. Both sub-types progress to Alzheimer's disease at the same rate. Until now it was not known if the pathologies of the two types of MCI were different, or if MCI-MCD was just a more advanced form of MCI-A.
Researchers found that the hippocampus of the patients with MCI-A was 14 percent smaller than that of the healthy subjects, nearly as great as the 23 percent shrinkage seen in Alzheimer's disease. But, the hippocampus of those with MCI-MCD most resembled that of the controls, showing only 5 percent shrinkage.