Diaphragm Strength in ALS Assessed by Magnetic Stimulation of the Phrenic Nerve Roots

Gary Mills, Michael I. Polkey, Catherine Lloyd, Malcolm Green, John Moxham, P.N. Leigh
Tuesday April 15 3:00 pm / Exhibit Hall A

Assessment of inspiratory muscle strength is of prognostic value in ALS, but traditional measures (the vital capacity or static inspiratory pressure) are volitional; i.e. they depend on patient aptitude and motivation. Additionally they are difficult to perform maximally in the presence of bulbar or facial muscle weakness. Measurement of transdiaphragmatic pressure during cervical magnetic stimulation of the phrenic nerve roots (Tw Pdi) is a recently described method of measuring diaphragm strength which is acceptable to patients. We therefore used this technique to assess the prevalence of diaphragm weakness in ALS. With this technique the lower limit of normal for Tw Pdi is 19 cm H20 (Hamnegård et al Am J Respir Crit Care Med 1996;153;A785).

The patients were 28 consecutive referrals to a regional ALS centre, who received an El Escorial diagnosis of definite or probable ALS. They presented between 9 months and 5 years after the onset of symptoms.

Tw Pdi proved acceptable to the 26 of the 28 patients able to swallow balloon catheters. 5 patients were in ventilatory failure (i.e. PaCO2 > 6kPa). 19 patients had definite diaphragm weakness

Diaphragm weakness is common in ALS even in the initial stages. Measurement of Tw Pdi may be of potential value both in the clinical management of ALS and in clinical trials of new treatments Sponsored by: MNDA, Great Britain.

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