Decreased Bilateral Frontal Lobe Perfusion in Dementia of Amyotrophic Lateral Sclerosis

A 59-year-old woman with amyotrophic lateral sclerosis (ALS) and normal results of brain MRI was evaluated for slowly progressive dementia. A Tc-99m biscate (technetium 99m-biscate ethyl cysteinate dimer) study showed diffuse, regional decreased blood flow in the bilateral frontal lobes. This pattern conforms to the previously described pattern of bilateral decreased frontal lobe perfusion as quantified by O-15 water positron emission tomography and other blood flow tracers such as I-123 iodoamphetamine. This dementia associated with ALS is thought to be related to this pattern of decreased blood flow. MRI may show degeneration of the pyramidal tracts in patients with ALS, but this is an inconsistent finding. Tc-99m ECD brain SPECT may be useful to identify patients with dementia of ALS, thus differentiating this entity from other causes of dementia, such as Alzheimer's disease or multiple-infarct dementia from cerebral vascular disease. Identifying this pattern and establishing this diagnosis may obviate the need for further evaluation of potentially correctable causes of dementia.