Twelve-month duration as an appropriate criterion for flail arm syndrome

Objectives: To analyze the clinical features of flail arm syndrome (FAS) in a large Chinese clinic-based cohort, and to discuss whether it is proper to use a course of 12 months from symptoms onset as the criterion for FAS. Methods: This cohort study included patients with FAS or upper-limb-onset amyotrophic lateral sclerosis (UL-ALS) who visited Peking University Third Hospital between 2003 and 2013. Patients with FAS were diagnosed according to Wijesekera's definition, and patients fulfilling all the diagnostic criteria of FAS except that the course of disease was less than 12 months were defined as "FAS-type ALS". Group differences were analyzed using parametric and nonparametric tests as appropriate. Survival was analyzed using the Kaplan-Meier method and a Cox regression model. Results: One thousand nine hundred and thirty-five patients with ALS were recruited in the database, including 131 patients with FAS or FAS-type ALS and 767 with UL-ALS. The prognosis of FAS was significantly better than that of UL-ALS (p = 0.024) and FAS-type ALS (p < 0.0005), and the survival of patients with FAS-type ALS was worse than that of UL-ALS (p = 0.002). The difference in survival between those with proximal FAS (pFAS) and distal FAS (dFAS) (p = 0.188) was not significant. Conclusion: Since the prognosis of FAS-type ALS was significantly worse than that of FAS, our data suggest that a FAS subphenotype can be established after 12 months from first symptoms. It is important to note that FAS-type ALS phenotype may carry a worse prognosis than that of patients with UL-ALS.