While much emphasis on spinal cord injury/dysfunction (SCI/D) has focused on trauma, nontraumatic SCI/D is becoming increasingly common as the population ages. Nontraumatic SCI/D can be caused by a wide variety of etiologies. This chapter will provide a brief review motor neuron diseases (with primary emphasis on amyotrophic lateral sclerosis [ALS]), and myelopathies related to spondylosis, tumors, infection, vascular anomalies, and demyelinating disorders. Basic pathophysiology and rehabilitative techniques in nontraumatic SCI/D are in many cases similar as those in traumatic SCI (see Chapter 14 for a review of these topics.) A more focused review of inflammatory, infectious and cancer related SCI are found in Chapters 16 and 17, respectively.

Nontraumatic SCI/D represents a heterogeneous group of patients, and each underlying etiology presents a unique set of considerations in terms of diagnosis, treatment, and rehabilitation.

Background

ALS is a progressive neurodegenerative motor neuron disease resulting in muscle weakness, progressive disability, and eventually death. ALS primarily affects anterior horn cells of the spinal cord. Other motor neuron diseases such as poliomyelitis, Friedrich’s ataxia, and spinal muscular dystrophy, may be central or peripheral in nature. This review will focus on ALS, but the principles can be applied to any motor neuron disorder depending on the functional status of the individual.

Pathophysiology

ALS is characterized by the death of both lower (anterior horn cells in the spinal cord) and upper motor neurons (motor cortex). Typically, either lower or upper motor neurons are affected at the onset, but eventually both are involved.¹

The underlying etiology which causes ALS has not been fully described. Nevertheless, numerous cellular processes have been associated with the disorder; these include apoptosis, mitochondrial dysfunction, protein aggregation and generation of free radicals² (Fig. 15–1).

Epidemiology

ALS is the most common motor neuron disease, with an incidence of 2 per 100,000 persons.³ It has a predilection for people in their forties, fifties, and sixties, with peak incidence age 65 to 74.⁴

Clinical Examination

Objectively, the combination of both upper and lower motor neuron signs defines ALS. Fasciculations in the tongue and limb muscles along with weakness and wasting are typical. Deep tendon reflexes may be increased or decreased. Other upper motor neuron signs include the Hoffman’s reflex, Babinski’s reflex, clonus, and spastic gait. Pseudobulbar palsy and pseudobulbar affect may also be present. Dementia, most commonly frontotemporal, presents in approximately 10% of patients with ALS.⁵

Although the clinical manifestations of ALS are variable, typically patients first develop asymmetric weakness evident in a distal limb. Weakness without sensory loss is the hallmark of ALS. Initial phases of ALS present with muscle weakness, fatigue, and endurance deficits. Early morning cramping is experienced, which eventually evolves into spontaneous twitching or fasciculations of muscles. Interestingly, bowel, bladder, sensory, and cognitive functions are preserved even late into the disease process.

Gait impairment may present with foot drop or proximal muscle weakness, accompanied by muscle cramping. Degeneration of the corticobulbar projections into the brainstem is evident as patients display pseudobulbar palsy, in addition to difficulty chewing or swallowing. Bulbar weakness may also present with dysphagia, weight loss, dysarthria, excess respiratory secretions, and pseudobulbar affect. Late in the disease, as the severity of muscle weakness progresses the motor deficits becomes symmetric. The disease typically leads to death within 3 to 5 years after diagnosis, often due to respiratory failure.⁶

Diagnosis

Diagnosis involves both clinical and electromyographic findings. While the revised El Escorial criteria are the gold standard, the Awaji criteria may have greater sensitivity with similar specificity (Table 15–1).⁷

Medications

Riluzole, a glutamate inhibitor, is the only medication approved for ALS by the U.S. Food and Drug Administration (FDA) and is said to prolong life by a few months.⁵

Rehabilitation

Patients should be referred to a multidisciplinary clinic to optimize health care delivery and prolong survival.⁸ This typically involves a physician, physical therapist (PT), occupational therapist (OT), speech language pathologist (SLP), respiratory therapist, nurse coordinator, and social worker. The types of therapeutic interventions vary depending on the degree of disability.

The early stages often involve only mild weakness and endurance deficits, requiring fall assessments, gait analysis, spasticity management, and compensatory strategies. As the disease progresses, patients require increasingly intensive compensatory strategies and adaptive equipment. When making decisions regarding the ordering of durable medical equipment, providers should take into account future needs that would be anticipated as disability accumulates. Studies also suggest that moderate exercise may be safe for ALS while monitoring for signs of overexertion such as excess postexercise fatigue, muscle pain, and soreness affecting activities of daily living (ADLs).⁶ As swallowing function progressively declines, the transition to percutaneous endoscopic gastrostomy (PEG) has been shown to stabilize weight and prolong survival.⁹ Secretions may be managed by botulinum toxin injections or low-dose radiation therapy.⁸ Dysarthria can be progressive, and patients may benefit from augmentative and alternative communication (AAC) devices.

In the late stages as respiratory function declines, phonation and volume become limited. Advanced ALS presents with profound generalized weakness. End-of-life decisions such as nutritional support via gastrostomy tube, tracheostomy, and long-term ventilation are important to approach prior to these later stages.

Background/History

Several biomechanical spinal conditions may cause compression and resultant injury to the spinal cord (myelopathy). Spondylosis refers to chronic degenerative changes of the spine; in severe cases spondylosis may cause critical spinal stenosis and myelopathy (Fig. 15–2). Disc herniations, osteophyte formation, spondylolisthesis, and ossification of the posterior longitudinal ligament (OPLL) may occur in the aging spine, resulting in critical stenosis. Spondylolisthesis is defined as anterior or posterior displacement of one vertebral body over the vertebral body located below it, which can further exacerbate stenosis. Atlantoaxial dislocation refers to instability between the C1 (atlas) and C2 (axis) vertebra. It can result from trauma, congenital craniocervical abnormalities (as in Down’s syndrome), and chronic inflammatory conditions such as rheumatoid arthritis.

Epidemiology

Cervical spondylotic myelopathy (CSM) is the most common cause of nontraumatic SCI/D in older persons. It is more prevalent in males than females (2.7:1). The incidence is higher in people over the age of 50, and the most common level of involvement is C5–C6. The incidence of symptomatic lumbar spinal stenosis, which results in cauda equina compression and lower motor neuron findings, is four times higher than symptomatic cervical stenosis.¹⁰

Clinical Examination

Initial presentation can vary depending on the location and degree of compression of neural elements. Common presenting symptoms include neck pain/back pain, sensory and motor deficits in the involved extremities, and impaired gait or fine motor control. Bowel and bladder dysfunction can be seen in late presentations.

Spinal stenosis of the cervical and thoracic spine can result in myelopathy with upper motor neuron patterns of deficits. Stenosis in the lumbar regions can result in a cauda equina syndrome secondary to compression, with lower motor neuron findings. Neurologic exam findings are similar to those seen in incomplete traumatic SCI.

Disease-specific exam findings in spondylotic myelopathy includes:

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  Lhermitte’s sign: Electrical shock-like sensation that travels down the spine and limbs with flexion of the neck, which can be seen in CSM.

  
  
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  Reproduction of pain with lumbar hyperextension in cases of lumbar stenosis.

  
  
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  A palpable step-off is a very specific finding in spondylolisthesis but often missed during exam. An increase in lumbar lordosis is also frequently seen but is neither sensitive nor specific.

Diagnosis

Diagnosis of myelopathy due to spondylosis can be often challenging due to variable presentation, which can mimic several other neurologic conditions. Early recognition of myelopathy/cauda equina syndrome is important to reduce the risk of a delayed diagnosis and permanent disability from neurologic deterioration.

The differential diagnosis of CSM includes many of the other causes of nontraumatic SCI/D listed in this chapter. Cauda equina syndrome secondary to spondylosis can mimic acute inflammatory demyelinating polyradiculopathy (AIDP), ALS, diabetic neuropathy, and Guillain-Barré syndrome (GBS).

Imaging studies are critical in the diagnosis and for visualizing the extent of canal stenosis, spinal cord compression, and/or cauda equina compression. In those instances where imaging does not correspond to the physical examination findings, further workup is necessary.

Plain anteroposterior (AP)/lateral spine x-rays are recommended as initial imaging workup. Flexion and extension views can be ordered to check for instability. Lateral and oblique views can identify pars defects. Atlantoaxial instability can be revealed by open-mouth odontoid and lateral cervical spine radiographs.

Magnetic resonance imaging (MRI) studies are valuable for the demonstration of spinal cord compression and cauda equina compression. MRI also helps to differentiate these conditions from tumors, multiple sclerosis (MS), AIDP, and GBS due to their distinct patterns of enhancement.¹¹ MRI signal changes on T2 images are useful in outcome prediction and can serve as a prognostic tool.¹²

Computed tomography (CT): CT myelogram is useful when MRI is contraindicated. It is also helpful in the setting of artifacts from prior surgery. CT scan also provides better visualization of bony structures.

Electrodiagnostic studies: Electromyography and nerve conduction studies may aid in differentiating between patients with spondylotic neural compression and those with spondylosis without compression.

Cerebrospinal fluid analysis can help distinguish between neoplastic, vascular, infectious, inflammatory, or degenerative disorders.¹³

Motor-evoked potentials (MEPs) are valuable in measuring the extent of involvement of the corticospinal tract in patients with CSM. MEPs also play an important role in monitoring the effect of surgical treatment.¹⁴

Management Options

Neurologic deterioration has been noted in 20% to 60% of the patients without surgical intervention 3 to 6 years after initial diagnosis of CSM.¹⁵ The patients with mild CSM should be counseled regarding the natural history of CSM, and surgical options may be discussed. If the myelopathy deteriorates during conservative treatment, timely surgical intervention is effective.¹⁶

Surgical intervention had superior outcomes compared to nonoperative treatment in patients with moderate-to-severe CSM.¹⁷ Early decompressive surgery is recommended in patients with rapid progressive clinical deterioration following the onset of cervical myelopathy or cauda equine syndrome.^18,19 Surgical decompression for CSM has shown improvement in functional, disability, and quality-of-life outcomes at one year of follow-up for mild, moderate, and severe CSM.²⁰ Optimal timing of surgical approach remains controversial.

Medications

Evidence from preclinical studies suggests that glutamate-related excitotoxicity may contribute to the pathology of myelopathy, and that riluzole, when combined with spinal cord decompression, may reduce this effect. Although riluzole is FDA approved and has been shown to be safe and effective for ALS, its efficacy and safety in CSM need further investiagtion.²¹

Therapies/Interventions/Alternatives

Intensive rehabilitation is recommended following spinal surgery due to the benefits in reducing pain, increasing spinal mobility, and ensuring faster return to work.²² The principles of spine rehabilitative therapy are to strengthen core muscle groups without compromising the integrity of the central canal and neural foramen. These are discussed in detail in Chapter 14.