Tartaglia et al considered which clinical features at onset and during follow-up could help differentiate between amyotrophic lateral sclerosis (ALS) and primary lateral sclerosis (PLS). At presentation, stiffness was the only symptom that was significantly different between PLS and ALS; it was higher in PLS. During follow-up, limb wasting was rare in patients with PLS. Disease duration was significantly longer in patients with PLS, and over 16 years of follow-up, mortality rate was better in patients with PLS. Further, a patient presenting with spasticity and not developing wasting within 3 years most likely has PLS.