Alzheimer’s disease: A progressive degenerative disease of the brain that leads to dementia. On a cellular level, Alzheimer’s disease is characterized by the finding of unusual helical protein filaments in nerve cells of the brain. These twisted filaments are called neurofibrillary tangles. In the brain, Alzheimer’s disease involves degeneration of the cortical regions, especially the frontal and temporal lobes. There is currently no cure for Alzheimer’s disease, but new medications and therapies appear to slow its progress and improve the patient’s ability to function.