We examined the relationship between time to involvement of LMN dysfunction and survival or disease duration in the population of 661 patients with ALS of whom 27 had signs or symptoms of spasticity at disease onset. The group of 27 ALS patients could be categorized into 2 groups: those who developed LMN dysfunction within 3 years (group A; n = 21; mean ± SD time to onset of LMN dysfunction, 1.38 ± 0.8 years; range, 0.35-3 years) and those who developed LMN dysfunction later in their disease course (group B; n = 6; mean ± SD time to onset, 17.31 ± 21 years; range, 3.86-58.5 years).
Tartaglia MC, Strong MJ. Clinical Differentiation Between Primary Lateral Sclerosis and Upper Motor Neuron Predominant Amyotrophic Lateral Sclerosis—Reply. Arch Neurol. 2007;64(10):1545. doi:10.1001/archneur.64.10.1545-b