Evaluation of diaphragm thickness at the apposition zone by ultrasound is a simple and well tolerated investigation in ALS patients.

The measurement of diaphragm thickness at the apposition zone in ALS patients is significantly correlated with the amplitude of the motor response by electric phrenic nerve stimulation.

Diaphragm thickness is independently correlated to maximal voluntary ventilation and forced vital capacity, which suggests that it gives important clinical information.