Neurospine 2020;17(3):513-524. Neurospine https://doi.org/10.14245/ns.2040464.232 pISSN 2586-6583 eISSN 2586-6591 Review Article Surgical Strategies for Cervical Corresponding Author Deformities Associated With Yo on Ha https://orcid.org/0000-0002-3775-2324 Neuromuscular Disorders Department of Neurosurgery, Spine and 1 1 2 2 2 Spinal Cord Institute, Severance Hospital, Jong Joo Lee , Sung Han Oh , Yeong Ha Jeong , Sang Man Park , Hyeong Seok Jeon , 2 2 2 2 2 Yonsei University College of Medicine, 50 Hyung-Cheol Kim , Seong Bae An , Dong Ah Shin , Seong Yi , Keung Nyun Kim , 2 2 2 Yonsei-ro, Seodaemun-gu, Seoul 03722, Do Heum Yoon , Jun Jae Shin , Yoon Ha Korea 1Department of Neurosurgery, Bundang Jesaeng Hospital, Seongnam, Korea E-mail: [email protected] 2 Department of Neurosurgery, Spine and Spinal Cord Institute, Yonsei University College of Medicine, Seoul, Korea Co-corresponding Author Jun Jae Shin https://orcid.org/0000-0002-1503-6343 Neuromuscular disorders (NMDs) are diseases involving the upper and lower motor neu- Department of Neurosurgery, Spine and rons and muscles. In patients with NMDs, cervical spinal deformities are a very common Spinal Cord Institute, Severance Hospital, issue; however, unlike thoracolumbar spinal deformities, few studies have investigated Yonsei University College of Medicine, 50 these disorders. The patients with NMDs have irregular spinal curvature caused by poor Yonsei-ro, Seodaemun-gu, Seoul 03722, balance and poor coordination of their head, neck, and trunk. Particularly, cervical defor- Korea mity occurs at younger age, and is known to show more rigid and severe curvature at high E-mail: [email protected], junjaeshin@ cervical levels. Muscular physiologic dynamic characteristics such as spasticity or dystonia gmail.com combined with static structural factors such as curvature flexibility can result in deformity Received: August 3, 2020 and often lead to traumatic spinal cord injury. In addition, postoperative complication rate Revised: August 21, 2020 is higher due to abnormal involuntary movement and muscle tone. Therefore, it is impor- Accepted: August 22, 2020 tant to control abnormal involuntary movement perioperatively along with strong instru- mentation for correction of deformity. Various methods such as botulinum toxin injection, physical therapy, muscle division technique, or intrathecal baclofen pump implant may help control abnormal involuntary movements and improve spinal stability. Surgical man- agement for cervical deformities associated with NMDs requires a multidisciplinary effort This is an Open Access article distributed under the terms of the Creative Commons Attribution and a customized strategy. Non-Commercial License (https://creativecom- mons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, Keywords: Neuromuscular disorders, Cervical deformity, Abnormal involuntary movement and reproduction in any medium, provided the original work is properly cited. Copyright © 2020 by the Korean Spinal Neurosurgery Society INTRODUCTION The overall prevalence of NMDs is approximately 72.6/100,000 population, ranging from < 0.2/100,000 population to 24.9/100,000 Neuromuscular disorders (NMDs) are a heterogeneous col- population for each disease (e.g., cerebral palsy, 9.8/100,000 pop- lection of various diseases and diagnoses caused by abnormali- ulation; multiple sclerosis, 18.8/100,000 population) in previous ties in upper motor neurons, lower motor neurons, peripheral studies. Most NMDs have a prevalence lower than 50/100,000 nerves, neuromuscular junctions, and muscles. NMDs frequent- population, making them very rare diseases.2,3 ly involve several organ systems and show various clinical man- From the perspective of spine surgeons, spinal deformities ifestations; for example, Duchenne muscular dystrophy involves which are one of the most challenging problems of the spine, skeletal muscle, smooth muscle, myocardial, endocrine, brain, are well known to be disproportionately common in patients and ocular abnormalities, which cause a variety of symptoms.1 with NMDs.4 In a previous report, spinal deformities were pres- www.e-neurospine.org 513 Lee JJ, et al. Surgical Strategies for Neuromuscular Cervical Deformities ent in 20% to 70% of cerebral palsy patients, depending on the few studies have investigated cervical curvature.8-10 In addition, severity of the disease, with prevalence rates of 60% in patients as NMDs themselves are rare, there is a tendency for reports to with Friedreich ataxia, 80% in patients with spinal muscular at- focus on cerebral palsy, which is a relatively common NMD.11 rophy (SMA), and 85% to 90% in male patients with Duchenne Generally, it has been reported that deformity curve progres- muscular dystrophy.4-6 Since the prevalence of spinal deformi- sion is more common in patients with NMDs than in adoles- ties requiring treatment in the adolescent population without cent idiopathic scoliosis (AIS) patients with similar patterns.12 NMDs is approximately 4 to 7 cases per 1,000, the relative prev- Also, unlike AIS, deformities in patients with NMDs occur more alence of spinal deformities in patients with NMDs is clearly frequently along with curve progression, even in adulthood af- much higher.4 ter growth, so NMD patients need constant follow-up in adult- Occipito-cervical or cervical area is a common region with hood. The course of NMDs itself affects deformity curve pro- spinal problems in patients with NMDs. Since the cervical spine gression. For example, progressive NMDs such as muscular dys- has a wide range of motion and complex functions, involuntary trophy are associated with more predictable patterns of defor- movement in NMDs can cause the development of an excessive mity progression than nonprogressive NMDs such as cerebral range of motion, resulting in cord compression that requires palsy.4 In a limited number of studies regarding curve progres- surgical treatment. These factors can generate a wide range of sion in untreated neuromuscular scoliosis, most cases of neuro- disorders and alignment pathologies necessitating surgical treat- muscular scoliosis were found to occur before 10 years of age. ment. In addition to structural parameters such as thoracic ky- The amplitude of the curve, whether the curve is thoracolum- phosis, other indicators reflecting the severity of NMD such as bar or lumbar, bedridden status, underlying disease severity, the Hoehn and Yahr stage are also associated with cervical posi- mental retardation, and functional status are factors known to tive sagittal malalignment.7 However, although cervical spine be related to curve progression. Gu et al.13 reported that patients deformities and NMDs have unique characteristics and sub- with a Cobb angle > 40° by the age of 12 were more likely to ex- stantially impact patients’ lives, few comprehensive studies have perience progression than those with a Cobb angle of ≤ 40° by focused on cervical deformities in patients with NMDs. There- the same age among 110 pediatric patients with a diagnosis of fore, in this article, we reviewed the existing literature on cervi- spastic tetraplegic cerebral palsy. Thometz and Simon14 report- cal spinal deformity surgery and sought to identify relevant sur- ed that curve progression was 0.8° each year in patients with gical strategies in patients with NMDs. curves less than 50°, whereas it was 1.4° in those with a curve more than 50°; they also reported that progression was more NATURAL HISTORY AND RISK FACTORS common in patients with spastic quadriplegia, a thoracolumbar FOR SPINAL DEFORMITY PROGRESSION or lumbar curve, and bedridden status. Some studies have also IN NMDS investigated spinal deformities in patients with Duchenne mus- cular dystrophy and pediatric spinal cord injuries, reporting Although the characteristics or types of spinal deformities in that both conditions are associated with a high incidence of NMDs may be similar in each disease, the natural history or spinal deformity and risk of progression.15,16 nuances of each underlying NMD that could affect spinal cur- Apart from the curve progression of the spinal deformity, the vature may be different. The progression of degenerative chang- progression of NMDs is known to cause pain and alterations in es throughout the whole spine in patients with NMDs is more skin integrity, difficulty in ambulation and position maintenance, severe than in patients without NMDs. Spinal deformity is a se- and most seriously, pulmonary and cardiac compromise, ulti- quela of childhood-onset NMDs and some adults with NMDs. mately causing mechanical effects on thoracic volume and com- The prevalence of scoliosis varied from 33% to 100% in the lit- pliance. Galasko et al.17 found that deterioration of pulmonary erature. By understanding the natural history of spinal deformi- function occurred simultaneously with rapid spinal deformity ties, we might be able to predict the probability and pattern of progression in untreated Duchenne muscular dystrophy patients. curve progression, and on that basis develop a treatment plan (e.g., the decision between surgical or conservative treatment), CHARACTERISTICS IN CERVICAL obtain informed consent from patients, and educate patients DEFORMITIES WITH NMDS appropriately. However, most existing studies have mainly fo- cused on the natural history of thoracolumbar curvature, and Cervical diseases in people with NMDs have different char- 514 www.e-neurospine.org https://doi.org/10.14245/ns.2040464.232 Lee JJ, et al. Surgical