We read with interest the article by Tartaglia and colleagues1 regarding the differences in disease course between patients diagnosed with primary lateral sclerosis (PLS) compared with those diagnosed with amyotrophic lateral sclerosis (ALS).
There is little doubt that the early appearance of prominent lower motor neuron (LMN) signs in a patient previously found to have a pure upper motor neuron (UMN) syndrome is a poor prognostic factor. The question still remains when, if ever, to draw a line between UMN-predominant ALS and PLS. Thus we would like to know whether analysis of the data acquired from periodic clinical and electrophysiological testing of patients who initially presented with an UMN syndrome (eventually diagnosed as having either PLS or ALS) allows an approximation of “time to LMN involvement” (TLMNI) for each patient. A graph plotting TLMNI against survival may provide some indication as to whether the separation of PLS from UMN-predominant ALS is clinically useful. Although it is inevitable that a longer TLMNI will be associated with longer survival, it is unclear whether prognosis improves steadily as TLMI increases. Finding that survival time correlates linearly with TLMNI would argue against the separation of these 2 entities. Conversely, a sharp increase in survival when TLMNI rises above 3 to 4 years would support the view that PLS should continue to be treated as a distinct clinical entity.
Gotkine M, Argov Z. Clinical Differentiation Between Primary Lateral Sclerosis and Upper Motor Neuron Predominant Amyotrophic Lateral Sclerosis. Arch Neurol. 2007;64(10):1545. doi:10.1001/archneur.64.10.1545-a