Differences in nerve excitability properties between isolated bulbar palsy and bulbar-dominant amyotrophic lateral sclerosis

ABSTRACT

Objectives: Isolated bulbar palsy (IBP) is a rare variant that can show a benign course, while progressive bulbar palsy (PBP) has been regarded as a bulbar-dominant type of classical amyotrophic lateral sclerosis (cALS). This study aimed to identify differences in the excitability properties between them.

Methods: We consecutively collected data on 22 ALS patients: 13 with cALS, 5 with PBP, and 4 with IBP. An automated nerve excitability test (NET) was applied to measure the strength–duration time constant, threshold electrotonus (TE), current–threshold relationship, and recovery cycle. The axonal excitability properties were compared between the ALS groups and 25 controls.

Results: Compared to controls, the cALS group showed a greater change in the depolarizing phase of TE of 90–100 ms after depolarizing current [TEd_(90–100)] (53.3±1.3 [mean±SEM] for cALS and 49.0±0.7 for control, P<0.01) and lower S2 accommodation (19.6±0.8 and 22.6±0.7, respectively; P=0.01). There was a nonsignificant tendency for a high TEd_(90–100) pattern to be less prominent in the IBP group than in the PBP group (51.5±4.22 and 48.8±1.5, respectively). In addition, all of the parameters of nerve excitability other than S2 accommodation in the PBP and IBP groups did not differ significantly from those in the controls.

Conclusions: The excitability properties of IBP and PBP differ from those of cALS. The pattern of NET in PBP was more similar to that in cALS than that in IBP. These findings suggest that IBP is a different entity from bulbar-dominant ALS and PBP.

KEYWORDS:

• Amyotrophic lateral sclerosis
• bulbar palsy
• nerve excitability
• threshold tracking
• differential diagnosis

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2017R1D1A1B03029672).

Notes on contributors

So Young Pyun

So Young Pyuna was a PhD student of professor Bae and finished her thesis last year. She is now raising her children and having some rest.

Yerim Kim

Yerim Kim was a neurology specialist and working for Kangdong Sacred Heart Hospital and Busan Paik Hospital, respectively. The authors’ aim with this article is to categorize one of rare variants of bulbar onset amyotrophic lateral sclerosis and investigate its pathophysiology in peripheral nerve axon level.

Seong-Il Oh

Seong-Il Oh was a neurology specialist and working for Kangdong Sacred Heart Hospital and Busan Paik Hospital, respectively. The authors’ aim with this article is to categorize one of rare variants of bulbar onset amyotrophic lateral sclerosis and investigate its pathophysiology in peripheral nerve axon level.

Jong Seok Bae

Jong Seok Bae is professor in Neurology at Hallym University, Korea. He has been working as the chairperson and neurology specialist at department of neurology, Kangdong Sacred Heart Hospital in Seoul. His research has mainly focused on Clinical neurophysiology and neuromuscular disorders. In particular, his major interest is ionic biophysics and excitability properties of peripheral nerve axon in motor neuropathy or motor neuron diseases. In addition, he is now the editor-in-chief of Journal of the Korean Neurological Association.