Platelet Calmodulin Levels in Adolescent Idiopathic Scoliosis (AIS): A Predictor of Curve Progression and Severity?

Introduction: Abnormalities of skeletal muscle and platelets have been identified in patients with AIS. Calmodulin is a calcium binding receptor protein which mediates muscle contractility (actin and myosin) in the platelet. Previous studies have suggested a possible direct relationship between calmodulin and curve progression based on a single calmodulin determination correlated with serial radiographs.

Purpose: To determine whether serial platelet calmodulin levels correlate with curve progression and severity in patients with AIS over a period of time during growth.

Materials and Methods: 55 patients with AIS of varying degrees of severity and curve types (King I–IV) were followed longitudinally during the growth period with simultaneous erect PA radiographs and blood draws for platelet calmodulin. There were 51 females and 4 males. Treatment consisted of observation in 28, brace treatment in 17 and spinal fusion in 10 patients. Tanner scores as well as Risser signs were recorded at each visit.

Results: In the 13 patients with > 10° progression there was a 100% positive correlation with increasing calmodulin levels. In the 42 patients with nonprogressive curves, 31 (74%) had stable calmodulin levels (P< 0.0001).

Calmodulin levels were generally higher in patients with curves > 30° compared to those with curve < 30°. Patients with double primary curves had higher calmodulin levels than patients with thoracic, thoracolumbar or lumbar curves. P–values were 0.018, 0.025 and 0.052 respectively. Calmodulin levels decreased in patients undergoing either brace treatment following surgery or at skeletal maturity.

Conclusions: It appears that increasing platelet calmodulin levels correlate closely with curve progression and severity and that both treatment (brace or surgery) and skeletal maturity correlate with decreasing calmodulin levels. Further investigation is necessary to determine whether in conjunction with standard radiographs, calmodulin may serve as a biochemical marker to assist in following patients with potential curve progression and to identify curves which have stabilized.