Right temporal variant frontotemporal dementia with motor neuron disease

Patterns of atrophy in frontotemporal dementia (FTD) correlate with the clinical subtypes of behavioral variant FTD (bvFTD), semantic dementia, progressive non-fluent aphasia (PNFA) and FTD with motor neuron disease (FTD-MND). Right temporal variant FTD is associated with behavioral dyscontrol and semantic impairment, with tau abnormalities more common in right temporal bvFTD and TDP-43 accumulation in right temporal semantic dementia. However, no clinical and anatomical correlation has been described for patients with predominant right temporal atrophy and FTD-MND. Therefore, we performed a database screen for all patients diagnosed with FTD-MND at Mayo Clinic and reviewed their MRI scans to identify those with striking, dominant, right temporal lobe atrophy. For cases with volumetric MRI we performed voxel based morphometry and for those with brain tissue we performed pathological examination. Of three such patients identified, each patient had different presenting behavioral and/or aphasic characteristics. MRI, including diffusion tensor imaging in one patient, and FDG positron emission tomography revealed striking and dominant right temporal lobe atrophy, right corticospinal tract degeneration, and right temporal hypometabolism. Archived brain tissue was available in two patients; both demonstrating TDP-43 type 3 pathology (Mackenzie scheme) with predominant neuronal cytoplasmic inclusions. In one case, neurofibrillary tangles (Braak V) and neuritic plaques were also present in keeping with a diagnosis of Alzheimer's disease. There appears to be an association between FTD-MND and severe right temporal lobe atrophy. Until further characterization of such cases are determined, they may be best classified as right temporal variant FTD-MND.