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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