Clinical and electrophysiological characteristics of respiratory onset amyotrophic lateral sclerosis: a single-centre study

Background We compared the clinical characteristics of patients with respiratory, bulbar and limb onset amyotrophic lateral sclerosis (ALS) who visited a single tertiary centre for 8 years. Methods Total of 115 ALS patients with respiratory, bulbar and limb onset ALS, including sex, body mass index (BMI), presence of lung disease, age at diagnosis, disease duration after initial symptoms, ALS Functional Rating Scale (ALSFRS-R) and progression rate (Delta-FS), pulmonary function, amplitude and distal latency (DL) of the phrenic nerves and blood creatine kinase (CK) and uric acid levels were collected. Results The prevalence of respiratory, bulbar and limb onset ALS were 5.2%, 28.7% and 66.1%, respectively. The mean age at diagnosis and ALSFRS-R were 67.8 +/- 5.5, 63.8 +/- 10.1 and 59.2 +/- 11.7 in the descending order. The mean amplitude (0.18 +/- 0.10 mV) and DL (9.5 +/- 1.7 ms) of the phrenic nerves were significantly decreased and prolonged in respiratory onset ALS compared with other types of ALS patients. Patients with respiratory onset ALS had normal creatine kinase (CK) levels, whereas patients with other types of ALS had increased CK levels. Conclusions Although rare, respiratory onset ALS may occur and should be considered during the initial differential diagnosis. In this study, patients with respiratory onset ALS were characterised by male predominance, with a higher baseline ALSFRS-R, lower BMI and phrenic nerve study well discriminated respiratory onset ALS from bulbar or limb onset ALS patients.