Disease duration of progression is helpful in identifying isolated bulbar palsy of amyotrophic lateral sclerosis

Background: Compared with typical bulbar onset amyotrophic lateral sclerosis (ALS), isolated bulbar palsy (IBP), an often under-understood variant of ALS, is characterized by symptoms confined to bulbar region for extended periods and relative preservation of limb and ventilation function. To find a cutoff value of disease duration that can distinguish IBP from typical bulbar onset ALS well, the association of survival with disease progression in bulbar onset ALS patients was analyzed.

Methods: Clinical data of bulbar onset ALS patients were collected from January 2009 to December 2013. The duration from bulbar onset to first significant limb involvement was analyzed by a cutoff point analysis with maximally selected log-rank statistics and dichotomized to categorize patient outcomes. The patients were divided into two groups, the IBP and typical bulbar onset ALS groups, according to the cutoff value. Clinical features were compared.

Results: 115 bulbar onset ALS patients were recruited, and the duration from bulbar onset to first significant limb involvement was associated with survival (P < 0.001). The cutoff duration was 20 months. 19 patients were identified as IBP and 96 patients as typical bulbar onset ALS using 20 months as the cutoff duration. Female was more common, limb weakness was less frequent and pure upper motor neuron (UMN) bulbar signs were more frequent in the IBP group than in the typical bulbar onset ALS group (P = 0.047; P = 0.004; P = 0.031). The median survival time of the IBP group was significantly longer than that of the typical bulbar onset ALS group (64 months and 26 months, respectively; P < 0.001).

Conclusions: A cutoff duration of 20 months from bulbar onset to first significant limb involvement may be used to specifically distinguish IBP from typical bulbar onset ALS. IBP was characterized by female predominance, relative preservation of limb function, more pure UMN bulbar signs and a relatively benign prognosis.