ABSTRACT
Although historically amyotrophic lateral sclerosis (ALS) has been considered to be a disorder restricted to the motor system, an association between dementia and ALS was first noted in the late 1800s and studies dating back to the 1930s documented dementia syndromes in ALS (1). In an extensive review of dementia with either ALS or Parkinson’s disease, Hudson concluded that dementia was indeed rarely associated with ALS (2). Subsequently, dementia in association with motor neuron disease (MND) was described by Mitsuyama and colleagues as a presenile dementia with executive dysfunction that later progressed to ALS (3,4). In 1994, the Lund and Manchester groups introduced the term frontotemporal dementia (FTD) with MND, to describe an entity in which MND was associated with ubiquitin-positive, tau-negative inclusions in the hippocampus, entorhinal cortex, and frontal neocortex (5). Until very recently, considerable debate surrounded the incidence, clinical, and neuroimaging features of dementia in ALS, with different terminologies utilized to describe the entity of ALS with frontotemporal lobar degeneration (FTLD). In part, this confusion arose due to the reliance upon Alzheimer’s disease (AD)-based dementia criteria for the assessment of cognition in the ALS population (6). These tools emphasize memory and orientation dysfunction, and are insensitive to the most common dementia associated with ALS in which the core features are executive dysfunction, behavioral disorders, and language impairment, reflective of a FTLD.
