How to recognize myelopathy

Any clinician who evaluates or treats spinal conditions, including simple low back or neck pain, should be aware of myelopathy. Myelopathy is often missed in the clinical setting, sometimes with devastating consequences.

The term myelopathy literally means sick spinal cord. Myelopathy is a clinical term implying that the spinal cord is dysfunctional or under duress.

There are many causes of myelopathy:

• Compression from overgrown bone and ligaments
• Disc herniation
• Intrinsic and extrinsic tumors
• Multiple sclerosis (MS)
• Amyotrophic lateral sclerosis (ALS)
• Syrinx formation
• Infection
• Inflammatory conditions

The most common causes of myelopathy are spinal cord compression and disc herniation.

How does spinal cord compression cause myelopathy?

Let’s take a closer look at the most common cause of myelopathy—spinal cord compression from degenerative changes of the spine.

Wear and tear changes occur within the spinal column throughout our lives; these are called degenerative changes or spondylosis. For example, discs lose water content, narrow, and bulge, facet joints become arthritic and hypertrophied, ligaments are put under more strain and thicken, and bone spurs (osteophytes) form at ligamentous attachments.

The net effect of these degenerative changes is that the width of the spinal canal can become significantly narrowed over time. Narrowing of the spinal canal is known as stenosis. If the stenosis is severe enough, it can result in compression of the neural elements such as the spinal cord in the cervical and thoracic spine, and the cauda equina in the lumbar spine.

If the process is slow enough, the nervous system will adjust to the compression and show little or no signs of duress. There is a limit, however, at which time the nervous system begins to become dysfunctional.

Sometimes, the loss of function from stenosis is reversible. But, one should never count on this, as the spinal cord is quite unforgiving. If the compression is acute, say with a disc herniation up against the spinal cord, the progression of dysfunction can be more rapid. In some cases, profound myelopathy can develop in a matter of hours or days.

However, when the spinal cord shows clinical signs of duress from persistent spondylotic compression, we say that the patient has spondylotic myelopathy.

Upper motor neuron signs

On the motor side, myelopathies affect mostly—although not entirely—upper motor neurons, which are neurons that descend from the brain to the anterior horn of the spinal cord. The axons of upper motor neurons are contained in various tracks of the anterior two-thirds of the spinal cord.

Upper motor neurons in the spinal cord have predominantly inhibitory fibers, which serve to smooth out and calm voluntary movement and reflexes. With the loss of upper motor neurons, muscles tend to become hypertonic, stiff, and spastic; muscle reflexes tend to become exaggerated or hypermetric.

As well, clonus and a Babinski sign may be present. Weakness can eventually occur but tends to be later in the progression of a slowly developing myelopathy. But, weakness may be profound in an acute compression of the spinal cord from disc herniation or other agents.

Muscle atrophy and fasciculations are not typical features of myelopathy, and normally point to a lower motor neuron injury. However, these findings can be seen in multilevel spinal cord compression if the anterior horn cells or nerve roots are also affected by the compression.

For example, in a patient with multilevel cervical spinal cord compression, there may be some lower motor neuron findings in the arms in addition to the upper motor neuron findings. This is due to compression of the anterior horn cell and nerve root. But, the lower extremities in this scenario should show only upper motor neuron findings.

Keep in mind, the mixture of upper and lower motor neuron findings in some cases of cervical spondylotic myelopathy can cause diagnostic confusion with ALS.

Sensory changes

On the sensory side, impaired proprioception is one of the earliest signs of myelopathy. Proprioception signals are carried predominantly in the large tracks running up the backside of the spinal cord. Later in the disease progression, the patient may lose light touch and pinprick sensation relatively symmetrically in the extremities and trunk.

With the loss of proprioception and increased muscle tone (with or without spasticity), the patient will be stiff, poorly balanced, and their gait becomes profoundly affected. Often, a dysfunctional gait will appear long before any weakness is evident, although the patient may report a sense of weakness due to the increased tone and loss of muscle control.

In the lumbar region, severe degenerative compression or a large central disc herniation will compress the cauda equina rather than the spinal cord. Therefore, findings in a severe case would include lower motor neuron dysfunction in the lower extremities (including weakness, atrophy, decreased tone, and decreased reflexes), sensory loss in the lower extremities, and possible bowel and bladder dysfunction. Upper motor neuron signs should not be seen with severe degenerative compression of the cauda equina.

Patients with myelopathy may present with vague complaints that focus predominantly on spinal pain, due to underlying degenerative changes. Therefore, it is necessary to actively look for myelopathy when evaluating a patient with what seems like a straight-forward spinal complaint. A myelopathy exam only takes a few minutes and can be easily incorporated into your general neurological and spinal exam.

Subjective history suggesting myelopathy

When assessing the patient, ask about changes in balance, unsteadiness (particularly in the dark), and falls. Get a sense of the speed of symptom progression. This can be extremely variable, ranging from hours to months!

Red flags signaling significant neurological compromise

Several signs and symptoms serve as red flags for disease processes that warrant rapid evaluation, due to a higher risk of significant neurological compromise. You should increase your suspicions that a serious pathological process may be taking place if the patient presents with one or more of these red flags:

• Trauma
• Cancer
• Systemic infection
• Intractable pain
• Rapidly progressive weakness
• Gait disturbance
• Paraparesis
• Urinary dysfunction

Physical exam for myelopathy

There are six tests that should be included in the patient’s physical exam to assess for myelopathy:

1. Active neck flexion and extension
2. Neurological exam
3. Crossed adductor sign
4. Muscle stiffness and rigidity
5. Sensory level
6. Proprioception

Active neck flexion and extension

On an exam, have the patient flex and extend their neck. In patients with myelopathy, this will sometimes precipitate tingling in all extremities. This is called Lhermitte's sign, and it may suggest severe cervical stenosis. However, it can also be seen with MS and other conditions.

Neurological exam

Go through your standard neurological assessment of the brain, cranial nerves, motor function, sensory function, deep tendon reflexes, coordination, and gait. Focus on reflexes—are any exaggerated? Is there clonus at the ankles? Does the patient have a positive Babinski sign?

Crossed adductor sign

Try tapping the medial thigh on one side and look for both thighs adducting. This is called a crossed adductor sign, which indicates loss of inhibition from upper motor neurons in the spinal cord.

Muscle stiffness and rigidity

Passively throw the patient’s extremities up in the air and catch them—do they seem relaxed and rubbery, or stiff and rigid? If they are stiff and rigid, the patient is demonstrating increased tone in their muscles.

Next, slowly and passively move the extremities around their joints. Is there a sense of involuntary resistance (i.e., rigidity) to them?

Sensory level

Look for a level where sensation changes abruptly over the trunk. Try this assessment with sharp sensations and light touch. This is known as a sensory level and is often many dermatome levels below the level of pathology. In other words, a patient with a pathological process occurring in the cervical spinal cord may be found to have a sensory level in the upper chest on the exam.

Proprioception

Loss of proprioception suggests a possible myelopathic process. One way to assess proprioception is by moving the patient’s big toes up and down without the patient looking. Ask the patient if they can tell which way you are moving them. The inability to differentiate indicates a loss of proprioception.

In any assessment of proprioception, you should always stand the patient up with their feet together and have them close their eyes. Excessive wobbling is called a positive Romberg sign. This indicates a loss of proprioception, which is often an early sign of myelopathy. Please note that you should be prepared to catch the patient when you perform this test!

As well, for a complete assessment of proprioception, don’t forget to observe the patient walking. Is the gait fluid with normal arm swing? Is it stiff, unsteady, or spastic? Sometimes, patients with severe spinal cord compression may seem relatively normal upon initial examination, but they wobble profoundly when they stand up to walk and need to reach for surfaces to stay upright.

It is critical to assess for myelopathy in all patients with spinal complaints. Myelopathic processes can leave patients permanently paralyzed or severely debilitated. Unfortunately, patients with cervical and thoracic myelopathy are often misdiagnosed with innocuous spinal disorders.

If myelopathy is detected, evaluation of its cause with magnetic resonance imaging (MRI) should be started immediately.

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