Alzheimer's disease or plaque disease? Two cases at the frontier of a definition

Atypical dementias confront the adequacy of current diagnostic concepts. The two patients with atypical dementia syndromes described here shared common postmortem features of numerous neocortical neuritic (senile) plaques and microvascular amyloid, sparing of hippocampus and substantia nigra, and the virtual absence of neurofibrillary tangles. Microscopically, the two differed only by the presence of a few subcortical Lewy bodies in case 1. These similar morphologic features were associated with dramatically different clinical presentations. In the first patient, visual hallucinations, Capgras' syndrome, cognitive slowing, myoclonus, parkinsonism, and primitive reflexes evolved over 3 years. Memory and language were relatively spared. In the second, dysphagia, nonfluent aphasia, hypophonia, motor perseveration, and a severe disorder of attention developed during this 18-month illness. At autopsy, an unrecognized colon malignancy was found. Despite high neuritic plaque counts in cortex, neither the clinical nor the pathologic criteria for Alzheimer's disease adequately describe either case. The cases will be examined first as clinical, then as neuropathologic, entities. From this approach, we conclude that a specific clinical dementia syndrome may be expressed by several neuropathologic "diseases" and that a variety of clinical syndromes may represent a single neuropathologic diagnosis. This strategy identifies a conceptual dichotomy between Alzheimer's syndrome and postmortem Alzheimer's disease. Meticulous clinical and neuropathologic observation is essential in advancing an understanding of the relationship between the two.