Diagnosing lumbar radiculopathy
Compression of lumbar nerve roots from disc herniation or overgrown spinal column components are common phenomena. Most often, they are relatively painless disorders.
On occasion, a compressed nerve root becomes irritated or inflamed and sets off a whole syndrome of pain and nerve dysfunctions. This disorder is known as radiculopathy.
Lumbar radiculopathy most commonly affects the L4, L5, and S1 nerve roots. Most lumbar radiculopathies are self-limited; given time alone, the majority of radiculopathies will improve and spontaneously go away—even if the compression remains.
For example, if lumbar radiculopathy occurs due to a herniated disc and then resolves over a few weeks, the herniated disc material will still be pressing up against the nerve for many more weeks or months. The body will eventually erode the extra material, but this takes time. In essence, the nerve root remains compressed yet it spontaneously feels better.
When should you consider lumbar radiculopathy as a possible diagnosis?
When assessing a patient to rule out lumbar radiculopathy, always be alert for red flags—signs that the condition may be related to more serious or urgent pathologies. Ask the patient if they have a history of any of the following:
- Recent trauma
- Rapidly progressive weakness
- Bilateral weakness
- Bowel or bladder dysfunctions
Always ask about bowel or bladder dysfunctions such as incontinence or retention. Acute spinal conditions (such as compressive metastatic tumors or cauda equina syndrome) often present with early bladder dysfunctions.
Keep the possibility of myelopathy or cauda equina syndrome in the back of your mind throughout your evaluation. These are serious conditions that may require urgent surgical intervention.
When obtaining a patient history, also inquire about treatments that have already been initiated in your patient.
If you still suspect lumbar radiculopathy after a subjective interview, assess your patient for two main symptom characteristics:
- Type, onset, and duration of pain
- Associated symptoms
Type, onset, and duration of pain
In lumbar radiculopathy, pain should be unilateral. Classically, it will be quite severe and more predominant in the leg than in the back. The pain tends to radiate from the back, through the buttock, and into the posterolateral aspect of the thigh and leg which can follow the dermatome of the affected nerve root (to a certain degree). Pain often radiates into the groin as well.
Patients tend to generalize pain and sensory symptoms, so be careful not to get too hung up on how closely the pain follows a dermatomal pattern. Pain does not have to follow a classical pattern. Most of the pain may be isolated to the buttock, the groin, a section of the leg, or the ankle. This makes forming a diagnosis quite challenging because many generalized low back pain syndromes and myofascial syndromes may radiate into part of the buttock and upper leg.
However, lumbar radiculopathy is often distinguishable because it will have a radiating quality all the way down the leg. Radicular pain can take on a host of characteristics such as shocking, searing, sharp, jabbing, or burning—and can be relentless.
When lumbar radiculopathy is suspected, ask the patient about paresthesia (pins and needles or tingling) and more unpleasant dysesthesia (burning, squeezing, crawling, or itching). These are commonly associated with radiculopathy pain and should follow a similar pattern down the leg.
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What to do if you suspect lumbar radiculopathy?
The diagnosis of lumbar radiculopathy is often made with history alone since physical exam findings can be rather unimpressive. On the other hand, positive findings help seal the diagnosis.
When performing a physical exam for lumbar radiculopathy, seven aspects should be considered:
- Physical and neurological exams
- Crossed straight leg raising exam
- Straight leg raising exam
- Related motor dysfunction
- Patellar and Achilles reflexes
- Sensory exam
During your physical examination of a patient with suspected lumbar radiculopathy, simply observe the patient for some time. Patients with severe radiculopathy are very uncomfortable and will assume bizarre positions in an attempt to somehow alleviate the pressure on the affected nerve root. A typical position that the patient may find more comfortable is lying on the exam table with several cushions under the affected leg. A patient in the seated position may lean their body to one side or the other.
Perform physical and neurological exams
Next, do a general physical exam and a focused neurological exam, being sure to include seven important assessments:
- Cerebral exam
- Upper extremity exam
- Coordination exam
- Cranial nerve exam
- Motor reflexes
- Sensory reflexes
- Deep tendon reflexes
There should be no upper extremity findings or myelopathic findings on the exam. There should also be no findings in the leg opposite to the painful leg.
Perform a crossed straight leg raising exam
With the patient lying on their back, gently extend the unaffected leg. If this causes pain in the affected leg, it is a strong sign of nerve root compression. This finding is called a positive crossed straight leg raising exam.
Perform a straight leg raising exam
To perform a straight leg raising exam, gently lift the affected leg and keep it straight, preferably with the patient supine. Raising the leg 10–15° should not increase the pain. If it does, suspect other pathologic disorders (or even malingering).
If the patient's radiating pain is intensified by raising the leg 30–45°, there is a good chance that they’re suffering from radiculopathy from a compressed nerve root. This finding is called a positive straight leg raising exam.
Flexing the ankle while the leg is raised often makes the pain even worse. These maneuvers irritate an afflicted nerve root because they stretch the nerve over the compressive entity (e.g., a herniated disc).
Interestingly, you do not usually see a positive straight leg raise exam in L4 radiculopathies, which tends to be more painful in response to extension of the leg at the hip. This exam is known as a reverse straight leg exam.
Look for related motor dysfunction
Next, look for evidence of related motor dysfunction. Remember, lumbar radiculopathy affects lower motor neurons. So, you should look for typical findings associated with lower motor neuron involvement:
- Decreased tone
- Decreased reflexes
Look for weakness in specific muscle groups. This means that the entire leg should not be weak. Also, it is unusual for a muscle group to have no function. If radiculopathy has been going on long enough, you may see atrophy in the affected muscles. Depending on the severity, this may range from weeks to months.
Affected patients tend to guard a lot, so muscle testing may be unreliable. This is often subconscious, and repeated encouragement usually gets them to make a full effort in each muscle group. If they are showing apparent weakness in several multiple groups, don’t give up! Push the exam until you are convinced of the findings.
Weakness, if present, should follow a pattern consistent with the nerve root being affected:
- L4 compression results in quadriceps weakness.
- L5 compression results in weakness in dorsiflexion of the foot and big toe.
- S1 compression results in weakness in plantar flexion of the foot.
Plantar flexion of the foot is best tested by having the patient heel raise on one leg at a time. The gastrocnemius is a strong muscle, and you may not be able to elicit weakness from a manual exam.
Bilateral weakness, or weakness that appears to involve multiple nerve roots, is not consistent with radiculopathy and suggests other disease processes or some psychosomatic element to the exam.
Assess patellar and Achilles reflexes
Reflex findings in patients with lumbar radiculopathy will be asymmetrical. A unilateral diminished reflex suggests nerve root dysfunction. To support your suspicion of lumbar radiculopathy, abnormal reflex findings should be associated with the affected nerve root:
- L4 compression results in a diminished patellar reflex.
- S1 compression produces a diminished Achilles reflex.
Other reflex findings
Hyperreflexia or a positive Babinski sign points to an upper motor neuron process. If the Babinski sign is present, you should be suspicious of a problematic spinal cord or brain and not a lumbar nerve root.
Perform a sensory exam
Do a sharp and light touch sensory exam in both legs and the trunk. Loss of sensation in an entire leg or both legs suggests other diseases or possibly a psychosomatic response.
With lumbar radiculopathy you should ideally find a specific dermatomal distribution of sensory loss that matches the nerve root that you suspect is compressed. However, sensory exams are notoriously inconsistent, so don’t be confused if there is a lack of perfect dermatomal distribution. Sensory loss approximating a whole dermatome or parts of one supports the diagnosis.
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