Degenerative Cervical Myelopathy as a Neuromuscular Mimicker

Degenerative cervical myelopathy (DCM) results from chronic compression of the cervical spinal cord by age-related changes of the vertebral bodies, intervertebral discs, and supporting ligaments (Figure 1).¹ Individuals with DCM can present with a wide range of neurologic symptoms, including bilateral hand paresthesias, loss of manual dexterity, gait dysfunction, recurrent falls, and neck, axial, and upper-extremity pain.² Neurologic examination classically reveals a combination of upper and lower motor neuron signs as well as loss of sensation to pain, temperature, vibration, or proprioception.³ DCM is often missed on initial presentation, and individuals may wait, on average, 1.5 to 2.2 years to obtain the correct diagnosis. The reason for misdiagnosis is unclear, but likely relates to the fact that individuals with DCM often have subtle and nonspecific signs and symptoms early on in their disease course that may overlap with many other neurologic conditions. Furthermore, there is a general lack of awareness for this condition among physicians and the general population. The aim of this article is to review the diagnostic challenges and neuromuscular mimics of DCM by reviewing 2 cases.

Case 1

IW, aged mid-70s, who had a history of diabetes, presented with a 1-month history of difficulty with buttoning shirts, hand clumsiness, and progressive gait disturbance. The symptoms started shortly after influenza vaccination. IW denied any sensory symptoms, but noted that tactile sensation in the hands was “different.” IW reported longstanding lower back pain, but otherwise did not complain of radicular neck or arm pain. IW initially denied bladder or bowel dysfunction, but later reported difficulty urinating.

Neurologic examination findings are presented in Table 1. This individual was referred for urgent outpatient EMG due to concern for Guillain-Barré syndrome (GBS), and EMG results demonstrated a length-dependent axonal predominant sensorimotor polyneuropathy most consistent with the known diabetes. Given ongoing symptoms, the decision was made to pursue spinal imaging, which provided diagnostic clarity (Table 1).

Assessment of Individuals With Potential Symptoms of DCM

The assessment of individuals with suspected DCM begins by asking both open-ended and myelopathy-specific questions (Table 2). These specific questions are important, because many individuals with DCM have a dominant and disabling symptom, and may neglect to report other symptoms unless asked directly. Furthermore, bladder, bowel, and sexual dysfunction are likely underreported by individuals with DCM due to general sensitivity discussing these symptoms, as well as the thought that these problems are either a common part of aging or secondary to an alternative diagnosis. Asking patients to detail the onset of their symptoms can also be useful for diagnostic framing. For example, a patient may have only noticed weakness in the hands for 1 month but failed to appreciate the significance of intrinsic hand muscle atrophy developing in the months prior. In addition, the clinical history should include a review of neurologic symptoms that, if present, may point to an alternative diagnosis.

A recent systematic review of the literature aimed to evaluate the diagnostic accuracy and frequency of various symptoms in DCM.² Table 3 summarizes the key findings from this review and highlights the heterogeneity of clinical presentations in DCM. In general, DCM should be included in the differential diagnosis of individuals presenting with hand clumsiness, hand or upper-extremity numbness or paresthesias, neck or shoulder pain, or gait impairment, and strongly considered in individuals with any combination of these symptoms. Of note, only 51% of patients with DCM reported neck or shoulder pain, which demonstrated that these symptoms are not required to make a DCM diagnosis.

The next step in evaluating an individual with DCM is to perform a comprehensive neurologic examination that assesses muscle tone, strength, reflexes, coordination, and sensation. Specialized reflex testing should also be considered to evaluate for evidence of upper motor neuron dysfunction. Table 4 provides an overview of the sensitivity and specificity of important examination findings in DCM.³

An important concept that is highlighted by case 1 is that individuals with concomitant neuropathy or lumbar spinal stenosis may not have classical upper motor neuron signs in their extremities due to a secondary process affecting the lower motor neurons and the normal reflex arc. The individual in case 1 had longstanding diabetes, with electrophysiologic evidence of a length-dependent sensory predominant axonal neuropathy; as a result, hyporeflexia/areflexia was present in the lower extremities on examination instead of the classical hyperreflexia seen in DCM. The correct diagnosis was ultimately made on the basis of the combination of symptoms along with narrow-based, unsteady gait.

Although the prevalence of peripheral neuropathy in older individuals is estimated at 7%, the actual prevalence is likely higher due to underdiagnosis.⁴ The frequency of tandem cervical and lumbar stenosis may be as high as 60%.⁵ Given how common these conditions are in the general population, it is important not to exclude DCM as a potential diagnosis in the absence of classical upper motor neuron signs. Interestingly, according to Rhee et al,⁶ ~21% of individuals with DCM who are treated surgically do not exhibit classical signs of myelopathy, further emphasizing the importance of clinical history in diagnosing DCM.

It is not surprising that GBS was the leading diagnosis given the onset of sensorimotor symptoms after inluenza vaccination and the patient’s clinical course. Typically, the rate of symptom progression differs substantially between GBS and DCM, with GBS resulting in rapidly progressive quadriparesis and sensory deficits.⁷ Although DCM commonly has a more insidious onset and a chronic course, there is a subset of patients who exhibit significant neurologic deterioration within 1 month of symptom onset.⁸ As such, it is important to consider DCM in the differential diagnosis of rapidly progressive sensorimotor symptoms and thoroughly review the myelopathy-specific questions outlined in Table 2.

Case 2

GF, aged mid-70s, presented with a 2-year history of spastic quadriparesis without sensory disturbances or bladder dysfunction.

Initial neurologic examination was notable for upper and lower-extremity spasticity, gait instability, and weakness of the right upper extremity without sensory disturbances.

MRI of the cervical spine revealed spinal canal stenosis at C4–C5, and GF underwent surgical decompression for presumed progressive DCM. In the months after surgery, GF experienced worsening spasticity in the lower extremities, further deterioration of gait, and new onset of dysarthria, as well as tongue and chin fasciculations. EMG was pursued and demonstrated evidence of denervation as well as reduced recruitment and chronic remodeling of motor units in bulbar, cervical, and lumbar segments. A diagnosis of amyotrophic lateral sclerosis (ALS) was ultimately made.

The Role of Imaging in the Diagnosis of DCM

In the setting of supporting signs and symptoms, a diagnosis of DCM is made by confirming the presence of canal stenosis and cervical cord compression on MRI.⁹ However, incidental degenerative spine changes are commonly found on MRI, especially in individuals age >60 years. A recent analysis by Smith et al¹⁰ estimated the prevalence of asymptomatic spinal cord compression in a healthy population to be ~24%. The rate of progression from radiologic spinal cord compression to DCM is ~1.8% per year, indicating that spinal cord compression often does not result in clinical signs and symptoms. There is no consistent association between DCM severity and certain imaging findings, including the degree of spinal canal stenosis or cord compression, sagittal alignment, or hyperintensity on T2-weighted imaging. Given the lack of concordance between MRI findings and symptoms, it is critical to have a high pretest probability of DCM before pursuing imaging.

As in case 2, ALS may be initially misdiagnosed as DCM, especially in its early stages, given similar features of upper and lower motor neuron dysfunction, as well as a similar age at onset. In addition, given the high prevalence of canal stenosis from degenerative spine disease, it may be difficult to prove that DCM is the underlying cause of certain symptoms. A total of 4.2% to 13% of individuals with ALS undergo spinal decompression for presumed DCM or lumbar spinal stenosis, resulting in a delay in diagnosis of ~13 months.^11,12 In individuals with isolated motor symptoms, electrodiagnostic studies should be considered to evaluate for evidence of ALS. Electrophysiology can be particularly helpful in distinguishing ALS from DCM if there are lower motor neuron signs in the thoracic or lumbar regions.

The Natural History of DCM

The natural history of DCM can help distinguish this disease from ALS and other neuromuscular mimics. Furthermore, knowledge of rates of disease progression may help determine which individuals may benefit from surgical decompression versus conservative management. In general, ~20% to 62% of individuals with DCM will exhibit worsening of their symptoms within 3 to 6 years if not managed surgically.¹³ In contrast, all individuals with ALS will experience a progressive decline in their physical function, due to worsening spasticity and weakness in their upper and lower extremities, respiratory insufficiency, and bulbar symptoms.

The slope and speed of disease progression in DCM are highly variable, with some individuals remaining stable and mildly symptomatic over time, and others progressing rapidly to advanced myelopathy. No clinical, imaging, or serologic biomarkers are available to help determine where an individual might lie on this spectrum. There is low to very low evidence supporting an association between neurologic deterioration and older age, increased myelopathy severity, longer duration of symptoms, circumferential spinal cord compression, or greater neck range of motion.¹⁴

Other Neuromuscular Mimics

Whereas ALS is an important mimic of DCM, individuals are more likely to be misdiagnosed with carpal tunnel syndrome, cervical radiculopathy, or another neurologic disorder.¹⁵ Table 5 summarizes the clinical history, examination findings, and cervical MRI results of common DCM mimickers. Table 5 also highlights the role of electrophysiology and other tests in distinguishing DCM from alternative diagnoses. As outlined in Table 5, there are important clinical history and physical examination features that can help narrow the differential diagnosis. The presence of lower motor neuron or upper motor neuron signs, or both, with or without sensory deficits can assist with localization and direct further workup (Figure 2).