Natural History of Pure Primary Lateral Sclerosis

Objective To assess if primary lateral sclerosis (PLS), classified as “pure” when the EMG is normal, converts to amyotrophic lateral sclerosis (ALS) after longitudinal follow-up. Methods Retrospective chart review of pure PLS patients at Mayo Clinic-Rochester (1990–2016). Inclusion criteria required a normal EMG during the first 4 years of symptoms. Results Forty-three patients had pure PLS (25 female, 58%) with median onset-age of 50 years (range: 38–78), and median follow-up at 9 years disease duration (range: 4–36). The ascending paraparesis phenotype (N = 30; 70%) was most common, followed by hemiparetic-onset (N = 9; 21%) and bulbar-onset (N = 4; 9%). Among the 30 paraparetic-onset cases, bladder symptoms (n = 18; 60%) and dysarthria (n = 15; 50%) were more common than pseudobulbar affect (n = 9; 30%); and dysphagia (n = 8; 27%); by last follow-up 17/30 (56%) used a cane; 6 (20%) required a wheelchair. The paraparetic-variant, compared with hemiparetic and bulbar-onset, had youngest onset (48 vs 56 vs 60 years, respectively; p = 0.02). Five patients died, 1 required a feeding tube, and none required permanent non-invasive ventilation. Two patients developed an idiopathic multisystem neurodegenerative disorder, which surfaced after 19 and 20 years. Two patients developed minor EMG abnormalities. The remainder 39 had persistently normal EMGs. Conclusions Pure PLS did not convert to ALS after median 9 years disease duration follow-up in our study population. The ascending paraparetic phenotype was most common, with earlier onset and frequent bladder involvement. After years of pure PLS