Agarwal S, et al. - Researchers assessed if primary lateral sclerosis (PLS) represents part of the amyotrophic lateral sclerosis–frontotemporal dementia (ALS–FTD) spectrum of diseases. Twenty-one patients with PLS were comprehensively assessed and outcomes were compared to patients diagnosed with pure motor ALS (n = 27) and ALS–FTD (n = 12). Researchers reported that the cognitive profile in PLS resembled ALS–FTD, except behavioral impairments were not prominent. Data presented showed a higher resting motor threshold in PLS than ALS and ALS–FTD, which was consistent with differential cortical motor neuronal abnormalities and more severe involvement of corticospinal axons, while short-interval intracortical inhibition, indicative of inhibitory interneuronal dysfunction was similar to ALS and ALS–FTD. The mechanisms underlying slow disease progression were likely to be distinct in PLS, still, these findings supported the idea that PLS lies on the ALS–FTD spectrum.