Surgical Management of Neuromuscular Kyphosis

Michael C. Gerling

Gary Ghiselli

Henry H. Bohlman

DEDICATION

This chapter represents Dr. Bohlman’s last literary work before his peaceful passing in May of 2010. Though it never previously culminated into a textbook chapter, the material content was a source of pride for Dr. Bohlman and was a topic of choice during Grand Rounds lectures spanning the globe. The role he played in advancing care of dropped head deformity is representative of Dr. Bohlman’s tremendous foresight and dedication to academics that has inspired an entire generation of distinguished educators and shaped the foundations of the field of spinal reconstructive surgery. Renowned as a true gentleman, Dr. Bohlman was a master clinician, educator, family man, and friend with a legacy that will live on as one of the great mentors of our time. He will be missed.

Neuromuscular kyphosis (NMK) is a rare, disabling condition with a predilection for the cervical spine where patients lose active control of neck extension while often retaining flexibility. NMK has been described by surgeons as chin-on-chest deformity, or dropped head deformity (DHD). The imbalance of the cervical soft tissue leads to a progressive kyphotic posture. During early stages of the disorder, the deformity is milder and horizontal gaze may be sufficient to carry out activities of daily living. These patients often escape detection with relatively small disability. However, as the disorder progresses, the ability of the cervical musculature to maintain horizontal gaze decreases, and external support may be necessary to carry out activities of daily living. Chronic cases often suffer from significant pain, dysphagia, dyspnea, myeloradiculopathy, and loss of motion secondary to ventral soft tissue contractures and muscle spasms. In some cases, patients may develop a compensatory head tilt or rotation to help them visualize the horizon using their lateral vision. This unique sagittal deformity is poorly understood and poses a considerable challenge to treating physicians and surgeons alike. This chapter reviews the current algorithm for operative treatment of NMK.

BACKGROUND

NMK was previously considered an ominous finding suggestive of systemic neuromuscular (NM) disease, often associated with amyotrophic lateral sclerosis (ALS) and myasthenia gravis (MG). Today, NMK is recognized in association with multiple systemic and focal disorders that impart muscular imbalance, with extensor muscle weakness or hyperactivity of the cervical flexor muscles. Table 89.1 outlines the spectrum of recognized etiologies of NMK.

CERVICAL MYOPATHY

NMK is now recently recognized as a distinct clinical entity without other findings suggesting a systemic NM disease (1). A focal myopathy of the cervical extensor muscles
occurs. The thoracic and thoracolumbar extensor muscles can be involved as well. Other than primary cervical myopathy (CM), the most common subtype of secondary myopathy is those patients with radiation therapy to the neck and chest. These patients can present decades after radiation treatment.

TABLE 89.1 List of Disorders Associated with DHD

Pathology
Motor neuron		ALS
		Postpolio syndrome, SMA
Peripheral nerve		Chronic inflammatory polyneuropathy
Neuromuscular junction		MG
Muscle
	Idiopathic	Primary CM (primary)
	Iatrogenic	Radiation-induced CM (secondary)
	Inflammatory	Polymyositis/dermatomyositis
	Congenital/hereditary	Inclusion body myositis
		Nemaline myopathy
		Mitochondrial myopathy
		Carnitine deficiency
		Unspecified congenital myopathy
		Fascioscapulohumeral dystrophy
Endocrine/metabolic		Cushing’s syndrome
		Hypothyroid myopathy
		Myotonic dystrophy with severe hypothyroidism
		Severe hypokalemic myopathy
Extrapyramidal		PD
		Tardive dystonia
Neoplastic		NF type 1
Other		Syringomyelia
		Camptocormia

Idiopathic or primary CM and secondary CM are reported in small case series with an incidence of 1.5% of patients presenting to a busy university-based neurology practice (1). The true incidence of the disorder is probably underreported by surgeons and other related medical providers. Early reports may have inaccurately diagnosed or characterized the pathology. In our experience, most patients have a delayed diagnosis; however, some authors describe it developing over a period of 1 week to 3 months (2). The milder kyphosis found early in the disease process is easily masked by its intrinsic flexibility and one’s ability to compensate with lumbar hyperlordosis. With more severe kyphosis, CM is often overlooked because of its insidious onset and low levels of pain in the majority of patients. Furthermore, the cervical curves are frequently continuous with the thoracic curvature and therefore easily mistaken for thoracic osteoporotic compression fractures and aging. In many cases, patients are told for years that nothing can be done for their disabling stooped posture, with no meaningful evaluation or treatment rendered.

Approximately one-half of patients have axial or shoulder pain and mild proximal weakness that may be related to abnormal postural mechanics. Degenerative changes, complications, and neurologic sequelae including radiculopathy and myelopathy are uncommon with few cases reported in the literature.

CAMPTOCORMIA

Camptocormia, otherwise known as Pisa syndrome or “bent spine” syndrome, is similar to CM, where diffuse weakness of spinal extensor muscles causes a flexible kyphotic deformity of the thoracolumbar and lumbar spine. It is rarely reported in association with DHD and occurs in conjunction with NM disorders, extrapyramidal disorders, paraspinal myositis, psychiatric disorders, and in idiopathic cases (3). It is poorly understood and only described in small case reports. Degenerative changes and neurologic deficits are typically absent and not attributed to the deformity.

The authors’ report on CM was the first description of postoperative outcomes in patients with camptocormia and the first to describe the disorder in association with radiation exposure. In both patients, the syndrome was recognized after cervicothoracic surgery when horizontal gaze was not achievable despite adequate correction of the occipital-thoracic sagittal balance. Paraspinal atrophy was noted in a continuum from cervical to lumbar regions of the spine. An excellent outcome was achieved after lumbar osteotomy in one of these patients described in the Case Example below. Figure 89.1 illustrates the sitting posture and sagittal balance of one of our cases. This patient refused further surgery and was grossly unsatisfied with his residual deformity.

CONGENITAL MYOPATHY

Nemaline myopathies are a genetically diverse group of congenital myopathies, which are characterized by formation of nemaline rods within muscle sarcoplasm or nuclei or both. In addition to sporadic forms, four clinical types of inherited nemaline myopathy have been identified:

1. Severe neonatal

2. Mild congenital (classic)

3. Adult onset

4. Childhood (autosomal dominant)

Clinically, nemaline myopathies present with proximal or generalized muscle weakness, often sparing bulbar muscles except the facial muscles that may be severely affected. Of 12 well-documented cases of adult-onset nemaline myopathy, neck extensor weakness was severe in 5 and present in another 3 (4).

NEUROFIBROMATOSIS

Spinal deformity associated with neurofibromatosis (NF) only occurs in the peripheral form of the disease, Von Recklinghausen’s disease (NF1). Though nondystrophic deformity occurs, the disease is best recognized for the predominant dystrophic changes associated with anomalies in the dura mater. The deformity most commonly occurs in the thoracic region with sharp angulated curves over short segments. Though it is less common, cervical kyphotic deformity is well documented in association with NF1. Cobb (5) was the first to describe the variable pattern of curvature that can occur and the catastrophic sequelae after laminectomies without instrumented stabilization procedures in kyphotic NF1 patients.

Figure 89.1. Camptocormia after dorsal spinal fusion for idiopathic CM and DHD.

Though cervical deformity is rarely associated with NF1, kyphosis is the most common manifestation. The lesions are usually dysplastic and often associated with dysplastic lesions in other regions of the spine. Reporting a series of 37 patients with thoracic scoliosis or kyphosis, Yon-Hing et al. (6) found 15 (44%) cervical spine lesions. Most lesions were asymptomatic without clinical signs. In another large series, 22% of patients suffered with deformity associated with head and neck masses. Case reports also document atlantoaxial dislocation in rare cases with NF1 (7).

The presentation of deformity associated with NF1 is distinct from typical DHD as it tends to be more focal and related to the location of the lesions. Dysplastic changes in the spinal column initiate the deformity, though extensor muscle failure through prolonged elongation may ensue. Accordingly, this chapter does not focus on surgical treatment of the NF1 disease entity.

EXTRAPYRAMIDAL DISORDERS

Cervical Dystonia

Cervical dystonia (CD), or “spasmodic torticollis,” is one of the most common forms of adult-onset focal dystonia, often presenting with a combination of cervical kyphosis and rotational deformity, while still maintaining some degree of flexibility. Kyphotic deformity occurs in cases where involuntary hyperactivity of ventral cervical muscles leads to imbalance and deformity demonstrated in Figure 89.2 and 89.2. Though most cases are idiopathic, multiple etiologies have been implicated, including genetic factors, cerebral palsy, trauma, dysfunctional sensory pathways, and basal ganglia impairment (8,9). In contrast with CM patients, structural degeneration and complication rates are common in patients with focal CD, estimated between 18% and 41%, including reports of disk herniation, spondylolisthesis, fractures, and neurologic sequelae such as radiculopathy and myelopathy (10).

Tardive Dystonia

Tardive dystonia, as described in the cervical region, is a milder form of tardive dyskinesia usually caused by neuroleptic medications. In many cases, this deformity is asymmetric with twisting of the head in addition to the hyperflexion. Reversal of this form of dystonia is attempted through movement disorder specialists with alterations in medication regimens.

Parkinson’s Disease

Parkinson’s disease (PD) is frequently associated with kyphotic spinal deformity that may be an adaptive mechanism when balance declines. There has been one case report of isolated neck extensor myopathy with parkinsonism (11). It is questionable whether the kyphosis is due

to the parkinsonian disorder or concomitant multisystem atrophy (3). Unusual intermittent episodes of camptocormia can in rare cases exacerbate their baseline impairment of balance with high risk of falling (12). Diagnosis is based on medical history and neurologic examination, as there are no laboratory tests that have proven helpful.

Figure 89.2. Relaxed supine.

Figure 89.2. Continued

Possible Pathophysiologic Factors

NMKs are, for the most part, age-related disorders. They occur mainly in those greater than 60 years old. In a recent study of 10 elderly patients with myasthenia gravis, age range 80 to 88 years, head drop was the most common presentation, occurring in 6 patients (13). Adult-onset nemaline myopathy patients have a high incidence of head ptosis as a presenting symptom (14). Katz and Pate proposed that in elderly patients, age-related loss of tissue elasticity and mild kyphosis predisposes to chronic stretch injury of paraspinal muscles and may contribute to head drop (15). In a study comparing the cervical paraspinal muscle morphology in patients with cervical myopathies and normal necropsy controls, necrosis, core-targetoid changes, type II atrophy, and type I predominance were seen in both groups with similar prevalence and severity (16). Similarly,
Simmons and Graziano (17) found similar changes in nine patients with kyphotic deformity associated with ankylosing spondylitis. The pathologic abnormalities were more common and severe with increasing age of patients in disease and control biopsies. Hence, it may be difficult to make a specific etiologic diagnosis by studying the paraspinal muscles alone.

There has been some debate whether there may be a neuropathic contribution to the pathophysiology of idiopathic head drop. The acute clinical course is reminiscent of the clinical course of Parsonage-Turner syndrome. Whether a similar process can selectively involve the cervical plexus and the dorsal spinal nerves only has not yet been determined (3).

DIAGNOSIS

Diagnosis begins with a complete history and physical exam. Neurologic conditions must be considered first because some are treatable. Therefore, a neurologist should be consulted at an early stage of the evaluation.

IMAGING

Plain radiographs of the cervical spine are essential for evaluation of all NM spinal deformities, including at least anterior-posterior and lateral films with flexion/extension to evaluate bony architecture, spondylosis, intersegmental instability and flexibility. We use long-cassette scoliosis films to include the base of the occiput and top of the sacrum on one film. It aids in the overall evaluation of sagittal balance in both the upright, flexed position and in the supine, fully extended position. In order to adequately evaluate extension, the patient should relax in a supine position on the table for approximately 15 minutes. In our experience, upright extension films usually require an assistant to prop up the patient’s head, and the majority of extension occurs at the occipital-cervical articulation.

Cervical oblique films are helpful in patients with radiculopathy, patients with NF1, or patients with dystrophic changes identified on prior studies. Oblique films demonstrate neuroforaminal dystrophic changes such as foraminal enlargement due to dumbbell lesions caused by intraspinal meningoceles, solitary tumors, or interstitial hypertrophic neuritis. Dorsal scalloping of the body and enlarged neuroforamina are indicative of intracanal lesions that can cause substantial compression of neural elements. These lesions can be extremely difficult to excise and cause considerable morbidity.

In some cases, better postural correction is seen on computed tomography (CT) scans and magnetic resonance imaging (MRI) where patients are supine for an extended time or given light sedation. Most surgeons use the brow-chin angle to assess the extent of cervical deformity as demonstrated in Figure 89.3.

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