Decreased body mass index and restrictive lung disease in congenital thoracic scoliosis.

BACKGROUND: Pediatric patients with congenital thoracic scoliosis often have restrictive lung disease and low body weight for age. In other patients with respiratory disorders, the work of breathing can increase basal metabolic demands and predispose patients to cachexia. The primary study aim was to determine if severity of restrictive lung disease, as measured by pulmonary spirometry, correlates to decreased body mass index (BMI) in patients with congenital thoracic scoliosis. A secondary study aim was to determine what patient factors and radiographic measures correlate to low BMI.

METHODS: Forty-nine consecutive patients with congenital thoracic scoliosis underwent pulmonary function testing, spinal radiographs, and BMI percentile for age calculations. Severity of restrictive lung disease was quantified by the forced vital capacity percentile (FVC%). The BMI percentile for age was also ranked as normal, moderately, or markedly decreased (0, <1, or <2 SDs below normal, respectively). The t tests were performed between BMI rank and FVC% as well as forced expiratory volume in 1 second (FEV1). A stepwise multivariate linear regression analysis was performed between BMI percentile and FVC%, age, sex, type and extent of previous spine fusion, radiographic measures, and pulmonary spirometry measures.

RESULTS: The mean BMI percentile for all patients was 43% (range, 2%-98%). Both FVC% and FEV1 percentile were significantly decreased in patients with abnormal BMI (77% vs 51%, P = 2.78 *10(-1) for FVC%; 75% vs 52%, P = 0.00021 for FEV1 percentile). Multivariate analysis showed that FVC% was the only tested variable that significantly correlated to BMI percentile. There was a 13.6 times higher risk of having an abnormal BMI in patients with moderate to severe restrictive lung disease.

CONCLUSIONS: Decreased pulmonary function compromise strongly correlates to low BMI in patients with congenital thoracic scoliosis. When considering moderate to severe restrictive lung disease as defined by FVC%, patients are at much higher risk of being significantly underweight. Body mass index is another important sign of thoracic insufficiency syndrome in these patients.

LEVEL OF EVIDENCE: Prognostic case-control study, level III.