Charcot-Marie-Tooth Disease (CMT)

Charcot-Marie-Tooth disease is named after the three physicians who described it in the late nineteenth century, and it is also known as hereditary motor and sensory neuropathy. It is not a single illness but a family of inherited neuropathies that share a common theme: the slow, length dependent degeneration of the peripheral nerves, the cabling that carries signals between the spinal cord and the muscles and skin of the limbs. Because the longest nerves are affected first, the feet and lower legs tend to declare themselves before the hands. The result is a characteristic picture of high arched feet, hammered or clawed toes, wasting of the small muscles below the knee, weakness of the ankles, reduced reflexes and a blunting of sensation in the feet and fingers.

The connection to the spine follows naturally once the underlying problem is understood. The spine is held upright and kept straight not by bone alone but by a continuous, finely judged effort from the muscles of the trunk: the long muscles running either side of the backbone, the deeper segmental muscles, and the abdominal wall. These muscles work in opposing pairs, and a straight growing spine depends upon their pull being roughly balanced across the midline. In a condition that interferes with the nerves supplying muscle, that balance can be lost. If the muscles on one side of the trunk pull a little more strongly or a little more steadily than those on the other, a young spine that is still growing can be drawn gradually into a curve. This is the essence of a neuromuscular scoliosis, and it is the mechanism that links a disease of the peripheral nerves in the feet and hands to a deformity of the spine.

It is worth being clear that not everyone with CMT develops a spinal curve, and that the great majority of the disability associated with the condition relates to the limbs rather than the back. The spine is, nonetheless, a recognised site of involvement, and the association is strong enough that curvature of the spine in a child is, in some forms of CMT, among the features that draw attention to the underlying neuropathy in the first place.

The association between CMT and curvature of the spine is one of the more consistent findings in the orthopaedic literature on the condition, even if the precise figures vary from study to study. Reported rates of scoliosis in CMT generally fall between roughly a tenth and a little under two fifths of patients, which is appreciably higher than the small percentage seen in the general adolescent population. The variation reflects differences in how the studies were conducted: the ages of the people examined, the particular genetic subtypes included, and the angle at which a curve was counted as a deformity.

The most frequently cited series give a useful sense of scale. A retrospective study of one hundred children with CMT found spinal deformity in well over a third of those with adequate radiographs, made up of scoliosis, kyphoscoliosis and pure kyphosis; among those followed to skeletal maturity, the proportion with a deformity reached half. A later study of forty-five children and adolescents with CMT and scoliosis examined how these curves behave and respond to treatment, and concluded that CMT scoliosis differs in important respects from ordinary adolescent scoliosis, with a marked tendency to an exaggerated forward curvature of the upper back. A large analysis of one hundred and seventy-five patients with hereditary motor and sensory neuropathy examined the deformities in detail and across genetic subtypes, reinforcing that spinal curvature is a genuine feature of the disease rather than a chance accompaniment.

Two themes recur across these studies. The first is that the deformity tends to appear during the growing years, often in early adolescence, with the average age at recognition in the region of twelve to thirteen. The second is that certain groups appear more susceptible, with female sex and the demyelinating type one form of CMT identified as carrying a higher likelihood of spinal involvement. These are tendencies described across populations, not predictions for any one person.

To understand why CMT scoliosis is treated as its own entity, it helps to set it beside the far commoner adolescent idiopathic scoliosis, the curvature that arises in otherwise healthy teenagers for reasons that remain unknown. The two can look superficially similar on an X-ray, but they arise from different roots and tend to behave differently.

Adolescent idiopathic scoliosis occurs in a child whose nerves and muscles are entirely normal; the curve develops despite a balanced muscular framework, and the trunk muscles, though they cannot prevent the deformity, work properly. A neuromuscular curve, by contrast, develops precisely because the muscular framework is no longer balanced. In CMT the imbalance flows from the unreliable nerve supply to the trunk and the muscles that stabilise the spine and pelvis. The curve is, in a sense, a downstream consequence of the neuropathy.

Several practical differences follow from this. Neuromuscular curves, as a class, are described as having a greater tendency to progress, to extend over longer segments of the spine, and to be accompanied by an exaggerated kyphosis, the forward rounding of the upper back, which in CMT is a particularly noted feature. Because the underlying muscular weakness does not resolve, the forces that produced the curve persist, and this is part of why bracing, which can be helpful in idiopathic curves, is generally reported to be less successful in CMT. The deformity also sits within a wider pattern of musculoskeletal involvement, alongside the foot deformities and, in some, abnormalities of the hips, so that the spine is one part of a broader picture rather than an isolated finding.

When the spine is viewed from the side rather than from behind, it shows a series of gentle, alternating curves: a forward hollow in the neck and lower back, the lordosis, and a backward rounding in the chest region, the kyphosis. These curves, taken together, make up what is called the sagittal profile. A recurring observation in CMT is that the curvature is frequently not confined to the sideways plane. An exaggerated rounding of the upper back, a thoracic hyperkyphosis, is described as a characteristic accompaniment of the scoliosis, so that the deformity is often a kyphoscoliosis rather than a pure sideways curve.

This sagittal dimension matters because it changes the character of the deformity and the way it is thought about. A combined curve places different demands on the trunk muscles, on balance when sitting and standing, and on the way the spine carries load. Where the muscles that would normally hold the upper back upright are weakened, the chest can drift forward into a stoop that the body then tries to compensate for elsewhere along the spine and at the pelvis. The recognition that CMT deformity has this strong forward component, rather than being a simple lateral bend, is one of the features that distinguishes it from ordinary adolescent scoliosis and one of the reasons it is followed and assessed in three dimensions rather than two.

A curve of the spine is never quite a problem of the spine alone, because the spine sits upon the pelvis, and the pelvis in turn depends upon the hips. CMT is associated not only with spinal deformity but, in a proportion of patients, with dysplasia of the hips, a condition in which the ball of the hip joint is incompletely covered by its socket. A large study of children and adolescents with CMT found hip dysplasia in a substantial minority, with rates that depended on the age examined and the genetic subtype, and noted that a number of these hips required surgical attention. The same neuromuscular imbalance that can draw the spine into a curve appears, in some, to affect the developing hip joint as well.

This matters to the spinal picture because the pelvis is the platform on which the whole spinal column rests. If the pelvis is tilted, a state called pelvic obliquity, the spine above it must accommodate the slope. In neuromuscular deformity generally, the relationship between the curve, the tilt of the pelvis and the position of the hips is considered together, because they form a single mechanical chain from the base of the skull to the feet.

CMT is genetically diverse, with a long and growing list of responsible genes, but a few patterns are relevant to the spine. The commonest form by a wide margin is CMT type 1A, caused by a duplication of a small piece of chromosome seventeen that carries the gene for a myelin protein called PMP22. This duplication accounts for a large share of all CMT and underlies the demyelinating type one disease, in which the insulating sheath of the nerves is primarily affected. It is this type one group that has been associated with a higher likelihood of spinal deformity.

A particularly instructive example, from a spinal point of view, is CMT type 4C, a recessively inherited form caused by mutations in a gene called SH3TC2. In this subtype, scoliosis and kyphoscoliosis are so consistent a feature that a series describing the condition found spinal deformity in almost all affected individuals, and frequently as the presenting complaint, the very first sign that brought the person to attention. CMT4C illustrates, more starkly than the commoner subtypes, that in certain genetic forms the spine is not a peripheral concern but a central part of the clinical picture.

The assessment of a spinal curve in CMT follows the same broad principles as the assessment of any scoliosis, but it is carried out in the knowledge that the patient has an underlying neuropathy, and this knowledge shapes the emphasis. Plain radiographs, taken with the person standing where possible, remain the foundation. They allow the curve to be measured by the standard Cobb angle, both in the sideways plane and from the side to capture the kyphosis, and serial films taken over time are the principal means of judging whether a curve is progressing during growth. Because the deformity in CMT so often has a forward component, the side view is given particular weight.

MRI is used where the spinal cord and nerve roots need to be examined, and to ensure that the curve is explained by the known neuromuscular process rather than by an additional structural problem within the spinal canal. Assessment of the hips and pelvis is considered alongside the spine because of the recognised association with hip dysplasia and because the tilt of the pelvis influences the curve above it.

The evidence on managing spinal deformity in CMT rests on retrospective series and the broader literature on neuromuscular scoliosis, rather than on large randomised trials. Observation is the course described for curves that are small and not progressing, with monitoring through the growing years by serial examination and radiographs to detect any change. Bracing, which has an established place in moderate idiopathic curves, is reported across the CMT literature to be of more limited value, because the persistent underlying muscular imbalance tends to work against it.

Surgical correction, in the form of a spinal fusion with modern instrumentation, is described in the literature for curves that are large or progressive. Reported outcomes have been broadly encouraging, with substantial correction of the curve achieved and, notably, without the high rate of complications that might be feared in a patient with an underlying neuropathy. A particular and well recognised consideration is the difficulty of intraoperative monitoring of the nervous system: because CMT affects the peripheral nerves, the electrical signals used during surgery to check the spinal cord and nerve pathways can be hard to obtain, and older series reported success in only a minority of patients. More recent work has shown that with technical refinements reliable monitoring can frequently be achieved in the CMT population.

In neuromuscular deformity the aim is not only to reduce the angle of the curve but to restore a balanced spine that sits squarely over a level pelvis, allowing comfortable, economical posture when sitting and standing. Because the deformity in CMT often combines a sideways curve with an exaggerated forward kyphosis, correction is considered in three dimensions, addressing both planes. The question of how far the correction should extend, and in particular whether it should reach down to the pelvis, is described in the literature as turning on the underlying disease and the behaviour of the curve and the pelvic tilt rather than on pelvic obliquity alone, and the recognised association of CMT with hip dysplasia adds to the importance of considering the spine, the pelvis and the hips together as one mechanical chain.

The outlook for the spine in CMT is, for most people, a secondary part of a condition whose principal effects are felt in the feet and hands, and many people with CMT never develop a spinal curve at all. For small and stable curves the picture is one of monitoring rather than intervention. For larger or progressive deformity, the surgical literature offers a measure of reassurance, describing substantial and durable correction with a complication profile that has not proved as forbidding as the underlying neuropathy might suggest, and with the historical obstacle of intraoperative monitoring increasingly surmountable. Any individual outlook is a matter for assessment by the treating team rather than something that can be read from a category or a measurement alone.

This page is general medical education and is not a substitute for individual advice. New or worsening weakness, numbness, saddle numbness or any disturbance of bladder or bowel control requires urgent assessment.

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This information is for general patient education and is not a substitute for an individual consultation. Always seek personalised advice from a qualified spinal specialist.