Frontal lobe degeneration of non-Alzheimer type. I. Neuropathology.

Among 158 cases of organic dementia in a prospective study concerning both psychiatry and regional cerebral blood flow there were 26 cases with a mainly frontal or fronto-temporal dementia. Careful neuropathological investigation disclosed 20 cases of a mainly frontal or fronto-temporal grey matter degeneration, in four of them compatible with Pick's disease (2.5%) whereas 16 cases (10%) appeared to form a separate group without histological Alzheimer features and therefore named 'frontal lobe degeneration of non-Alzheimer type' (FLD). The remaining group of dementias of a clinically similar type proved to consist of cases of Jakob-Creutzfeldt's and Alzheimer's disease with frontal predominance and also a case of normal frontal cortex with a projected dysfunction caused by bilateral thalamic infarctions. Also other similar conditions are accounted for from the literature. The validity of the pathological changes described here, particularly with regard to their severity and regional distribution as well as their tendency to spare certain areas is attested by the clinical picture including neuropsychiatric symptoms and the regional cerebral blood flow pattern, both consistently producing the picture of a frontal and fronto-temporal disease of a progressive degenerative type. These features are dealt with in the following papers by Gustafson (1987) and Risberg (1987). FLD is in some morphological respects similar to other dementing disorders such as the ALS dementia complex and progressive subcortical gliosis, though with both clinical and clear-cut pathoanatomical differences. For the time being it seems safest to conclude that we are faced with a hitherto not fully recognized if not a new type of dementia caused by 'simple' neuronal degeneration of mainly the frontal or frontal and temporal lobes. It makes up about 10% of organic dementias, a figure that would be higher in purely clinical classifications due to the admixture of other frontal lobe disorders or frontally projected dysfunction clinically simulating FLD of the pathoanatomical type here described.