Factor analysis of motor and nonmotor signs in essential tremor: Are these signs all part of the same underlying pathogenic process?

Essential tremor (ET) has traditionally been viewed as monosymptomatic. However, there is an emerging appreciation of an expanded number of motor manifestations as well as a new awareness of nonmotor manifestations. The current goal, through factor analyses, was to determine how these diverse signs relate to one another and shed light on their pathogenic bases. One hundred and thirty-eight ET patients had detailed neurological examinations. In these analyses, three separate factors emerged, explaining 58.7% of the variance. Factor I was comprised of the hallmark feature of ET, action tremor. It also included intention tremor, which is generally viewed as a sign of cerebellar dysfunction, and tremor duration. Factor II was comprised of cognitive test scores and age, and factor III, of rest tremor. Cognitive test scores did not fall into the same domain as motor features or tremor duration. These results suggest that: (1) the process that underlies cognitive dysfunction in ET is distinct from that which is responsible for action and intention tremors and their progression over time, and (2) cognitive dysfunction in ET is not likely due to cerebellar degeneration. Age loaded with cognitive test scores, further raising the possibility that age-related processes (e.g. Alzheimer-type changes) could underlie cognitive changes in ET.