Change in post versus pre-operative progression rate
To study the longitudinal course prior to and after surgery we analyzed 137 measurements of VC, 158 FVC measurements and 157 PEF results in 43 patients . There was no significant change in rate of decline in the VC, FVC and PEF (Table 3, Figure 1).
Discussion
This prospective cohort study on LFT results in children with neuromuscular and syndromic scoliosis with restrictive lung function disease shows no stabilization of lung function 3-4 months after surgery. The effect of surgery on the rate of lung function decline remains inconclusive in this study with 43 patients.
Research on the impact of scoliosis surgery on LFT results has yielded conflicting results.
Previous studies have reported that scoliosis correction has beneficial effect on respiratory function 1,8,9, while other studies, including a recent cochrane review in patients with Duchenne Muscular Dystrophy (DMD) 10, have demonstrated no obvious benefit in terms of respiratory function11–13.
In a very recent retrospective study Farber reported decreased VC after scoliosis surgery in 14 out of 20 patients with SMA and muscular dystrophies. They were not able to conclude on changes in rate of VC decline2. All patients with SMA in this study had a decrease in VC after surgery. A large proportion of patients in our study were patients with SMA. We compared prospectively collected LFT results before and after surgery, both in a predefined limited time range.
We hypothesized that 3-4 months after surgery, the majority of patients did not fully recover to their preoperative functional level14. For this reason, we also studied the course of LFT results over a longer period in a larger cohort than Farber2.
Contrary to our study, two recent studies did show a positive effect in terms of a decreased rate of decline in FVC after scoliosis surgery.1,9. This may be explained by the retrospective nature1 and inclusion of patients with less severe scoliosis 9.
We did not observe obstructive lung disease prior to surgery, in contrast a previous study: McPhail showed obstructive lung disease probably caused by mainstem airway compression from spine rotation in 33% of children with congenital scoliosis or syndromic scoliosis, compared to a population prevalence of 2 to 5% 15.
Our work has several strengths. First, we only included patients with (the risk of) restrictive lung disease and excluded idiopathic scoliosis. Even though we studied a heterogeneous group of patients, the majority of patients had a standardized VC <60% prior to scoliosis surgery, which a recent study found to be the most sensitive LFT for predicting prolonged postoperative mechanical ventilation4. Stabilization of lung function has major impact in these patients, as it probably results in a delayed onset of chronic respiratory failure and reduced incidence of RTIs.
Due to the prospective nature of the study, confounding was limited. None of the included patients with SMA or DMD initiated new therapies, like Spinraza or steroids during data collection. In addition, none of the patients initiated NIV during data collection. Previously published studies were observational 8,9,11 or retrospective1,12,13, increasing the risk of bias.
We acknowledge also several limitations of our work. The rate of decline in LFT results had broad confidence intervals due to small sample, which possible explains the non-significant mean change in progression rate. However, compared to other studies we included more patients1,2,8,11–13,16. The follow up time of our study was limited. Introduction of new therapies, like genetic therapies for SMA, or other confounding factors may complicate interpretation of observational studies with longer follow up. Accurate predicted values of LFTs are difficult to obtain, due to error introduced by methods of height estimation. However, armspan was used as a well-established alternative 17.
We included a heterogeneous group of patients. The surgical technique varied, although in majority of patients growth friendly surgery was used.
Unfortunately, we did not prospectively study the effect on Maximal Inspiratory and Expiratory Pressures (PImax and PEmax) . Saito retrospectively reviewed lung function and respiratory muscle strength preoperatively, 1 month and 6 months postoperatively in 16 patients with DMD. Although no significant difference was observed in FVC and VC, mean values of PImax and PEmax significantly improved postoperatively 16.
The question remains if the positive effect on PImax and PEmax in this retrospective study is the result of surgery. Also other factors such as training effect, chest wall configuration and stabilization may contribute to the results of Saito, as large variations of PImax and PEmaxare also observed in healthy children 18.
To increase the power, study the effect on individual NMDs and possibly compare different surgical techniques, a multicenter study is needed to include a large enough number of patients.
A Cochrane review concluded uncertainty of benefits and potential risks of scoliosis surgery in patients with DMD and stated that RCTs are needed to investigate effects of scoliosis surgery on respiratory function in patients with DMD 10. Although our study cannot conclude that pulmonary function is expected to benefit from surgical treatment, this not a reason to withhold this treatment for progressive scoliosis in neuromuscular patients since untreated patients develop severe deformities that cause pain and inability to sit straight and severe difficulties in daily nursing care.
Systematic data collection however should be standard to allow high quality comparative cohort studies.
Conclusion
This prospective cohort study on LFT results in children with neuromuscular and syndromic scoliosis with restrictive lung function disease shows no short term beneficial effect of surgery on lung function . The effect of surgery on the rate of lung function decline remains inconclusive.
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