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Neuromuscular Scoliosis
Neuromuscular scoliosis is a condition that affects children with neuromuscular disorders and is characterized by the presence of one or more abnormal lateral curvatures of the spine. This curvature causes the spinal column to bend to the left or the right, in the shape of an S or a C. Because there is such a wide variety of the types of diseases that may cause neuromuscular scoliosis, the clinical presentation and severity of this condition is extremely variable. However, most children with this disease have poor balance and poor coordination of their trunk, neck, and head. There is also a high frequency of concurrent kyphosis, which is an abnormal forward-bending curve of the spine. The condition is generally classified into two categories, based on the type of disease that the child suffers from, and which causes the abnormal curve. Neuropathic scoliosis involves diseases that are primarily afflictions of the neurvous system, such as cerebral palsy or spinal cord trauma, whereas myopathic scoliosis involves muscular disorders, like muscular dystrophy or arthrogryposis. Unlike the other types of scoliosis, treatment of neuromuscular scoliosis is very unpredictable, mostly because the abnormal curves of the spine are also unpredictable.
Facts about neuromuscular scoliosis:
- Scoliosis is technically defined by the presence of a lateral curvature in the spine of >10 degrees deviation from straight upright (described further in the 'n the 'How is neuromuscular scoliosis diagnosed?' section).
- The earlier the curve develops in neuromuscular scoliosis, the more likely it is to progress to a more severe curve. Likewise, the more severe a curve is when it is first detected, the faster it will progress, on average.
- Unlike most cases of idiopathic scoliosis, in which the curves occur in a limited region of the spinal column and are relatively short, so to speak, neuromuscular scoliosis is associated with long curves that often extend to the sacrum, the region at the bottom of the spinal column.
- Neuromuscular curves are often associated with a condition known as pelvic obliquity, in which the child's pelvis is unevenly tilted, with one side positioned higher than the other side.
- Children with neuromuscular scoliosis usually do not experience any pain from the condition.
The spine, or spinal column, as it is also called, is a complex structure made up of 33 vertebrae, or bony segments, arranged vertically in succession from just below the skull to the tailbone. The spine has two main functions: to support the weight of the skull and upper body, and to provide a protective encasement for the spinal cord, the long, cylindrical nervous structure that sends messages to and from the brain and the rest of the body. The vertebrae are attached to other vertebrae above and below them by a number of ligaments, thick fibrous structures found throughout the musculoskeletal system that attach bones to other bones. The spinal column is also surrounded by a large number of muscles, known as paraspinal muscles, which offer support for the spine and contract to dictate its movement. The connection points between the vertebrae are called joints, in which small areas of smooth cartilage lined with a lubricating material, known as synovial fluid, allow the bony vertebrae to slide past each other with minimal friction, allowing movement. Unlike joints such as the knee or elbow, which allow for considerable movement, each joint of the spinal column allows for very little movement because of the number of tightly attached ligaments, thereby ensuring the strength and stability of the vital supportive column. However, the joints of the spine act collectively, with the sum of movements in all the joints allowing movements such as bending forward, back, and to the side.
The normal spine actually has a number of natural curves to it, which stems from the evolution of humans from four-legged mammalian ancestors who walked on the ground bent over, with the spine parallel to the ground. However, these normal curves are antero-posterior curves only; that is, they can only be seen when looking at the spine from the side. On the other hand, when looking from directly behind or in front of a person, the spine maintains a rigid upright structure, like a straight line. In other words, there are normally no lateral curves to the human spine. This upright structure is maintained by the body's natural positioning system, known as proprioception. When we move around on a normal basis, special nerve sensors called proprioceptors in the regions of all of our joints send millions of rapid signals to the brain with even the slightest movements. The brain processes all of these signals, monitoring exactly what the different parts of the body are doing, and sending signals back down to the muscles to alter the position of our body parts. Because the spine is made up of a large number of joints, all of which have their own proprioceptors, the brain is able to maintain finely tuned control over the paraspinal muscles and preserve its straightness, eliminating even the slightest lateral curves on a normal basis. Should there be even minor defects in the communication from the proprioceptors to the brain, in the brain's processing of the signals, or in the tone or contraction of the paraspinal muscles, one's ability to maintain an upright position would be compromised.
Because these myriad neuromuscular diseases are so varied in their clinical presentation, the actual pathophysiology (i.e. the set of events or process that ultimately brings about a condition) of scoliosis in these diseases is also varied. However, there are several features that are common across many, if not all, of the predisposing diseases.
Causes of neuromuscular scoliosisUnlike idiopathic scoliosis, which is the most common type of scoliosis and does not have an established cause, neuromuscular scoliosis is generally quite well understood, with regard to causation. In all cases, the underlying neuromuscular condition is felt to be the trigger for the development of scoliosis.
In neuropathic scoliosis, defects or abnormalities in the central nervous system (i.e. the brain and spinal cord) leads to altered proprioception, described above, or diminished control of the paraspinal muscles. As a result, abnormal forces will be transmitted upon the vertebral units of the spine, either because the muscles show increased motion (termed spasticity, as seen in cerebral palsy), decreased motion (also referred to as flaccidity, as occurs in Friederich's ataxia), or motion that is out-of-sequence (called dyskinesia, also seen in cerebral palsy).
Myopathic scoliosis is caused in a similar fashion, but through the direct affects of various diseases upon the muscles themselves, despite normal nervous systems. In many of these conditions, the most common of which is muscular dystrophy, the muscles undergo atrophy, or gradual wasting of the muscle tissue. Because the muscles will atrophy at different rates, scoliosis can result when the paraspinal muscles or other muscles of the trunk waste more quickly or significantly on one side of the body than the other, if even in a very small section of the spine. This throws off the stability of the spinal column, and leads to the curvatures seen in scoliosis. Other muscle diseases, such as arthropryposis, cause contractures of the muscles, which means they are excessively flexed, and remain fixed in a contracted position because of fibrosis of the muscles. This can occur in trunk and paraspinal muscles, obviously transmitting abnormal lateral forces on the normally symmetrical spine.
Because the neuromuscular changes in so many of these diseases arise in childhood, the spine is still in the process of growing when it experiences these abnormal forces, which generally worsens curves as growth spurts occur.
Diagnosing neuromuscular scoliosisNeuromuscular scoliosis is usually first detected during a standard physical examination by a pediatrician, noticed by a child's parents, or during a full workup for the child's neuromuscular condition. The physical will be followed by a series of x-rays, which allow for a more precise measurement of the possible presence and severity of one or more curves. As previously mentioned, this requires the presence of a curvature angle of at least 10 degrees, measured with the Cobb method.
A full neurologic exam of the back and extremities will be performed to insure that no other spinal conditions are present and that the spinal cord is not being affected by the presence of the abnormal curvature, if it is not already affected by the underlying condition. Occasionally, a spinal MRI, another radiological imaging technique, will be taken to compliment the spinal X-rays.
How is it treated?Decisions regarding the appropriate treatment for neuromuscular scoliosis depend on the severity of the spinal curvature at the time of the diagnosis, the age of the patient, and the symptoms of the existing neurological or muscular disorder. The curves in almost all of the predisposing diseases have a high rate of progression, and almost all children will therefore require surgery at some point. However, in some instances, bracing, though not a definitive form of treatment, will be utilized to slow the progression of the curve until a later time that surgery can be safely performed.
Bracing treatment usually involves wearing an external brace when the child is upright, but not when they are sleeping or lying flat. Though there are a number of braces available for treatment of scoliosis, the molded TLSO brace (thoraco-lumbo-sacral orthosis) is the preferred design, because it is effective when worn periodically and does not significantly constrict breathing, as might occur with some of the other designs. In general, the brace should improve a patient’s ability to sit or stand, as well as perform certain functions otherwise not possible. The brace should be worn for only several years, or until the decision has been made to pursue surgical treatment. Wheelchair seating adaptations also exist that can act similarly to bracing, and may be appropriate for some patients.
Surgeries for neuromuscular scoliosis are relatively complex, because of the other biological effects that are common in underlying neuromuscular diseases, such as respiratory difficulties, weak bones, and poor nutrition. Operations generally consist of instrumentation, in which metal rods are attached to the spine to maintain curve correction and spinal fusion, in which two or more of the vertebrae are fused together with bone bridges made of bone grafts. Fusion between the spine and the pelvis may also be necessary with cases of pelvic obliquity and particularly in children with muscular dystrophy. Surgeries may be performed through a posterior approach, in which the operation is performed with an incision in the back, or also with an anterior approach, which is a more extensive surgery that requires making an opening in the chest wall to reach the front part of the spinal column. Because of the stability and effectiveness of the devices used in these spine operations today, patients usually do not require bracing treatment following surgery, and hospital stays are usually limited to 7 to 10 days.
Coping with neuromuscular scoliosisThe development of scoliosis on top of an existing neuromuscular condition can be a difficult challenge for children and their parents alike. Surgery at a young age, if necessary, can seem somewhat daunting as well. However, because of the affects that scoliosis can have if left untreated, it is imperative that parents promptly seek out diagnosis and management of the condition by an orthopaedic surgeon. Surgical treatment of neuromuscular scoliosis is generally quite successful in reducing curves and improving the quality of patients' lives. Our pediatric group here at the NewYork-Presbyterian Morgan Stanley Children's Hospital is dedicated not only to the outcome of the treatment steps along the way, but also to the end goal of making your child's present and future life as comfortable, happy, and fulfilling as possible.
