Scoliosis is a common complication present in various neuromuscular diseases that develops as a result of progressive muscle weakness in the paraspinal musculature [
]. Neuromuscular scoliosis typically appears during advanced stages of disease, and this form is progressive and associated with deformities of the sagittal plane [
]. However, the most common form of this deviation is adolescent idiopathic scoliosis (AIS) which is a tridimensional deformity, defined as lateral deviation of the spine associated to vertebral rotation, with also sagittal plane implication. It occurs without a known cause in adolescents who do not exhibit neurological or muscular disorders or other diseases [
Core myopathy constitutes a group of congenital myopathies that present histopathologic features of focal reduced oxidative activity in muscle biopsies and they are clinically and genetically heterogeneous [
]. Core myopathy was initially described by Magee and Shy in 1956 as having a low incidence, although recent studies have shown a broader clinical spectrum for this condition, which suggests that the real incidence is considerably higher than previously described [
We evaluated two patients with a diagnosis of AIS by collecting muscle multifidus biopsies during the surgical correction of their scoliosis deformities. During the histopathologic evaluation of these muscle fragments, we noted the presence of multiple core structures indicative of congenital core myopathies [
The clinical presentation of core myopathies can be widely variable, although most patients develop hypotonia or delayed motor development in early childhood. More severe presentations, such as fetal akinesia, as well as milder clinical scenarios of adult onset have also been described as manifestations of these myopathies. Furthermore, orthopedic complications such as scoliosis, congenital hip dysplasia, foot deformity, ligamentous laxity and patellar instability have also been associated with congenital myopathies [
]. The only clinical manifestation found in patients was the scoliosis. They demonstrated motor and neurological development adequate for their age. However, the presence of core myopathy symptoms without any associated weakness is not sufficient for a diagnosis of core myopathy [
The presence of progressive scoliosis in the two patients discussed here could be associated to the weakness of the paraspinal musculature. This weakness would be result of a mild form of myopathy or related to physiopathology of the AIS. The musculature analyzed was the multifidus, that arise from mammillary processes and pass to the spinous processes two to four level rostrad. Its main function is to act as agonist of the rotational movement of the spine [
]. Thus its dysfunction could cause a rotational deformity, characteristic of AIS.
Of the known causative factors for the development of core myopathy, genetic factors seem to be most important, as mutations in the skeletal muscle RYR1 gene and less frequently in the SEPN1 gene contribute to disease development. The genetic analysis of the patients was not performed because initially the muscle disease was not suspected. After examination of biopsies and the central CORE histopathological finding, the next step will be to analyze the genetic code. However, this may require time due to the size of the mutations associated to the central CORE. It is important to explain that biopsies are routinely performed due to a research protocol of the institution in order to investigate the role of muscle balance in adolescent idiopathic scoliosis. The patients in this report had no relatives with deformities or altered motor development.
Previous studies have demonstrated a clear association between RYR1 gene mutations and susceptibility to malignant hyperthermia, which is a pharmacogenetic predisposition to potentially deadly adverse reactions that occur in response to volatile anesthetics and muscle relaxants [
]. This susceptibility is of particular interest to spine surgeons, as it can lead to progressive idiopathic scoliosis and require surgical treatment.
Because of the important association between scoliosis and paravertebral muscle imbalance, numerous studies have evaluated biopsies of the spinal rotator muscles for potential changes that may elucidate the etiology of AIS [
]. Here we describe two patients with clinical and radiological findings of AIS who were operated on and subjected to multifidus muscle biopsy, which demonstrated anatomopathological results suggestive of core myopathy.
Regardless of clinical outcome, the reported changes in the patients may help to understand the real influence of the rotator muscles of the spine in the etiology and perpetuation of “idiopathic” scoliosis adolescents. It is necessary further studies with histopathological evaluation of paravertebral muscles in a larger number of patients to elucidate the role of muscle in the etiology and pathophysiology of AIS. However, if genetic analysis of these patients will be positive for genes related to myopathy CORE, these patients developed a secondary scoliosis and, therefore, they can’t be classified as idiopathic scoliosis.
The authors declare that they have no competing interests.
RPL conceived of the study, and participated in its design and helped to write the manuscript. EBP, DEM, FF, DDC and LMRR participated in its design and helped to write the manuscript. BS and ASBO participated in the histopathological analysis and drafted the manuscript. MW conceived of the study, and participated in its design and coordination and helped to draft the manuscript. All authors read and approved the final manuscript.