Effects of scoliosis on respiratory muscle strength in patients with neuromuscular disorders

Abstract 

Background context

Neuromuscular disorders (NMD) are characterized by loss of lung volume and respiratory muscle weakness, but the effects of scoliosis on lung function are unclear.

Purpose

To compare pulmonary function and respiratory muscle strength in patients with NMD with and without scoliosis as well as in healthy controls.

Study design/setting

Prospective comparison of pulmonary function testing and respiratory muscle strength were made at the pediatric pulmonology and cardiopulmonary rehabilitation units of a university hospital.

Patient sample

Twenty-two patients with NMD and scoliosis, 17 patients with NMD without scoliosis, and 24 age- and sex-matched healthy controls. Outcome measures were compared in patients with NMD with and without scoliosis and healthy subjects using Student t test, Mann-Whitney U test, chi-square test, one-way analysis of variance (ANOVA), Kruskal-Wallis one-way ANOVA, Pearson correlation coefficients, and Spearman rank correlation, as appropriate.

Outcome measures

1) Pulmonary function: forced vital capacity (FVC), forced expiratory volume in 1 second (FEV₁), peak expiratory flow rate (PEF), forced expiratory flow between 25% and 75% of FVC (FEF_25–75%), and maximum expiratory flows at 75%, 50%, and 25% of FVC (MEF₇₅, MEF₅₀, and MEF₂₅, respectively); 2) oxygen saturation: pulse oxymeter reading; and 3) respiratory muscle strength: maximal inspiratory mouth pressure (MIP) and maximal expiratory mouth pressure (MEP).

Methods

Pulmonary function, oxygen saturation, MIP, and MEP were measured and compared in patients with NMD, patients with and without scoliosis, and in healthy subjects.

Results

The patients with NMD, both with and without scoliosis, had significantly lower PEF, MIP, MEP, % predicted MIP (%MIP), and % predicted MEP (%MEP) than those of healthy subjects (p<.05). The patients with NMD and scoliosis had significantly lower values than those with NMD without scoliosis and controls (p<.05) for FVC, FEV₁, and FEF_25–75%.

Conclusion

Both inspiratory and expiratory muscle strength were diminished in patients with NMD compared with healthy controls. Significant differences were also noted in pulmonary function in patients with NMD with or without scoliosis. This suggests that NMD may impact respiratory function independently of the effects of scoliosis. Clinicians treating patients with NMD should be aware of the possibility of compromised respiratory function in these patients to address possible complications.

Keywords: Neuromuscular disorders, Lung function, Respiratory muscle strength, Scoliosis