Phrenic nerve stimulation is more sensitive than ultrasound measurement of diaphragm thickness in assessing early ALS progression.

AIMS OF THE STUDY

To compare the assessment of respiratory decline with conventional tests, measurement of diaphragm compound muscle action potential (CMAP) to phrenic nerve stimulation and diaphragm thickness to ultrasound (US) investigation in amyotrophic lateral sclerosis (ALS) patients followed for a short period of time.

PATIENTS AND METHODS

We evaluated in 40 consecutive ALS patients, the clinical functional scale (ALSFRS-R), forced vital capacity (FVC), maximal voluntary ventilation (MVV), maximal inspiratory (MIP) and expiratory (MEP) pressures, sniff nasal inspiratory pressure (SNIP), Diaphragm-CMAP (latency and amplitude) and diaphragm US (maximal and minimal diaphragm thickness during full inspiration and expiration, respectively). Patients were evaluated at study entry and 4 months later.

RESULTS

Clinical functional assessment (ALSFRS-R), MEP, SNIP, and Diaphragm-CMAP amplitude declined significantly. Conversely, FVC, MVV, MIP, and diaphragm thickness showed a non-significant decline. We found significant correlations between all variables measured at both evaluation times.

CONCLUSION

In this study, we included patients who might be potentially eligible for a clinical trial and re-evaluated them within 4 months. In this short time, diaphragm thickness as assessed by US is not sensitive to detect changes. However, Diaphragm-CMAP amplitude was confirmed to be a sensitive non-volitional method to measure respiratory function in ALS.