Indicators of need for mechanical ventilation in Duchenne muscular dystrophy and spinal muscular atrophy

The purpose was to investigate a possible relationship between different parameters of physical function, spirometric measurements, and the approaching need for mechanical ventilation.

A nonrandomized, prospective, descriptive study of 11 patients with spinal muscular atrophy type II (SMA-II) and 14 patients with Duchenne muscular dystrophy (DMD). At a home visit, the anthropometric indices of age, height, and weight were recorded, the degree of disability was scored, and measurement of the strength of eight muscle groups and spirometry was performed. The interdependence of the variables was analyzed and the intergroup differences evaluated. Eighteen months later, it was found that one of the authors (B.J.), who was blind to the results of the first examination had instituted home mechanical ventilation on seven of the patients. The data were analyzed retrospectively for their predictive value as indicators of approaching ventilator dependency.

The seven patients who needed mechanical ventilation were the patients with DMD with the highest disability score (Egen Klassifikation [EK] sum > 20) and the smallest values for FVC < 1.2 L (FVC% < 30). We found a significant correlation (p = 0.002) between FVC% and the EK sum at the first examination and between the FVC% and the time until treatment with mechanical ventilation was instituted (p = 0.023). Although 7 of the 11 patients with SMA type II had FVC below 1.2 L and some of them had an EK sum score higher (indicating more disability) than some patients with DMD who needed mechanical ventilation, none of them required mechanical ventilation.

In this investigation, a combination of EK sum and FVC% provided a better indication of the approaching need for mechanical ventilation in the patients with DMD than the variables separately.