Slower Progression Rates in Lower Limb-Onset ALS

Objectives: The aim of this study was to assess the differences in diagnostic delay and disease progression in people with ALS (PALS) based on site of onset. Methods: A retrospective analysis of prospectively collected data was performed, including all PALS seen in the ALS clinic in the Hadassah Medical Center between January 2009 and March 2022. PALS were divided to three groups based on site of onset (upper limb onset-ULO, lower limb onset-LLO, or bulbar onset-BO). A linear mixed-effects model was constructed with the following variables: diagnostic delay, site of onset, age of onset and time since the initial visit. The model was applied to the ALSFRS-R total score and the bulbar and motor subscales. Results: Data from 1255 visits of 281 PALS were included in the study. PALS with LLO had longer diagnostic delays than PALS in the BO group. Slower decline of total ALSFRS-R score was observed in younger PALS, and in PALS with LLO when compared with PALS with BO or ULO. The slower decline of ALSFRS-R in PALS with LLO was due to a slower decline in the motor subscale. Longer diagnostic delays were associated with lower total ALSFRS-R scores at the initial visit and with slower rates of decline. Conclusions: Comparison among PALS with ULO, LLO and BO revealed differences in the diagnostic delay and in the rate of functional decline, suggesting that differentiating between ULO and LLO ALS may be useful in the stratification of PALS in clinical trials.