Radiculopathies and Plexopathies

Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is the procedure of choice to evaluate and characterize lesions affecting spinal nerve roots. With disc protrusions, MRI enables visualization of effacement of the nerve root by the herniated nucleus pulposus. In children, MRI imaging is useful to identify and characterize intra- and extramedullary lesions causing nerve root compression and radiculitis.

Electromyography

Nerve conduction studies are generally normal in radiculopathies. Intraspinal lesions, such as those seen with a herniated nucleus pulposus, occur prior to the bifurcation of the spinal nerve, affecting both its anterior and posterior primary rami. With compression of a single nerve root, motor nerve conduction studies tend to be normal because typically only a fraction of nerve fibers in the root undergo axon loss, and because of the overlapping segmental innervation of many muscles. At the same level the sensory nerve action potentials (SNAPs) are also normal, because the dorsal root ganglion is distal to the site of the damage, residing within the intervertebral foramen ( Figures 12.2 and 12.3 ). This is true for all cervical and lumbosacral root levels except L5, where up to 30% of dorsal root ganglia are intraspinal and therefore vulnerable to compression from disc extrusion, resulting in an abnormal superficial peroneal SNAP amplitude. Electromyography (EMG) in radiculopathies is more sensitive to changes affecting a single nerve root, showing signs of denervation (spontaneous discharges such as fibrillation potentials), in the paraspinal muscles as well as other muscles of the myotome corresponding to that spinal level.

In contrast, when the lesion is distal to the intervertebral foramen, the posterior ramus is spared and EMG of the paraspinal muscles is normal, while EMG of limb muscles shows the characteristic changes of denervation. One important caveat to the EMG assessment of radiculopathies in children is that, when they are anxious or upset, it can be difficult to obtain enough paraspinal muscle relaxation to adequately evaluate for abnormalities.

Children with peripheral nerve trauma may have both nerve root avulsion and plexus injuries. In the pediatric age group, therefore, EMG findings compatible with a primary plexus lesion (i.e. absent SNAPs) do not exclude additional damage at the nerve root level ( Figure 12.4 ). A combined process should always be considered in patients with possible proximal nerve lesions.

Etiology

Most cervical radiculopathies in childhood follow trauma or traction injuries (see Case Example 12.1 ), but tumors, inflammatory lesions and other extramedullary lesions can also cause nerve root compression or injury ( Box 12.1 ).

Clinical Presentation

It is important to be familiar with the clinical characteristics of radiculopathies at each spinal level, because these lesions may mimic much more common clinical entities, such as mononeuropathies or plexopathies. Most individuals with cervical radiculopathy have cervical or periscapular pain, which often radiates into the arm. With traumatic radiculopathies, this pain may precede the onset of numbness by 4 to 8 weeks, can spontaneously improve, and can then be followed by paresthesia and weakness a few weeks later. C7 or C6 nerve root lesions typically present with numbness affecting digits two or three, in a similar distribution to a median neuropathy. In contrast, C8 radiculopathies cause sensory symptoms involving the fifth digit, mimicking the distribution of the ipsilateral ulnar nerve or medial cord of the brachial plexus. When there is weakness, the triceps muscle is particularly affected in C7 lesions and the pronator teres and flexor carpi radialis in C6 radiculopathies; and the intrinsic hand muscles, flexor pollicis longus, extensor pollicis longus, and extensor indicis proprius are typically weakened by C8 nerve root lesions.

Differential Diagnosis

Refer to Box 12.2 for a list of differential diagnoses, discussed in the following subsections.

Etiology

On the rare occasions that intervertebral disk herniation occurs in children, it usually occurs in the lumbosacral area. See Box 12.3 for reported causes of pediatric lumbar radiculopathies.

Most cases are in adolescent boys. Trauma, related to sporting activities, lifting, falls, or occupational injuries, accounts for at least one-third to one-half of pediatric lumbosacral radiculopathies. The youngest such case was of a 27-month-old boy who fell from his crib. A significant proportion (13–57%) of adolescents with lumbosacral disc disease has a first-degree relative with a similar history, suggesting a genetic component to this condition.

Scoliosis surgery also predisposes to development of pediatric lumbosacral radiculopathies. One series attributed a 29% incidence of these lesions postoperatively to either surgical trauma or traction in the lumbosacral area. Intraoperative spinal monitoring may aid prevention of this surgical complication.

Developmental anomalies involving intramedullary and extramedullary structures can impinge on the spinal roots, causing pain, weakness and sensory changes.

Nerve root tumors occasionally present with radicular pain radiating into the lower extremities, with or without sensory changes and focal weakness. Reported causes of this syndrome include schwannoma, leukemia, synovial sarcoma, osteoblastoma, osteosarcoma, and aneurysmal bone cysts. Treatment of childhood malignancies with chemotherapy, radiotherapy, and bone marrow transplantation may also be followed by radiculitis.

Clinical Presentation

Most children present with back pain and sciatica. Pain is not invariable; occasional children develop a painless scoliosis. Children aged less than 10 years present with irritability, paravertebral muscle spasm, and leg weakness.

Neurologic deficits are usually relatively subtle and apparent at only one spinal level. A mild degree of focal weakness is seen in 32–60% of adolescents, most often involving the L5 musculature (tibialis anterior, extensor hallucis, and/or extensor digitorum). This is not generally severe enough to cause a foot drop. Well-defined sensory loss may or may not be present. In addition, paravertebral muscle spasm with concomitant limitation of spinal motion, cough-sneeze exacerbation (76%), and/or a positive Lasègue sign are often apparent. Most adolescents have pain on straight-leg raise or back motion. Disturbances of bladder and bowel function, however, are very rare and should prompt consideration of intrinsic cord dysfunction.

Evaluation

Routine spinal radiographs may demonstrate congenital bony and spinal segmentation anomalies, but the significance of these is often uncertain. A combined diagnostic approach including lumbosacral X-rays, lumbosacral spine MRI, CT imaging in certain cases, and—when these studies are nondiagnostic—EMG, has been recommended for diagnosis of lumbar nerve root disease in teenage children.

Differential Diagnosis

Infections, malignancies, and spinal injuries or developmental disorders such as spondylolisthesis should be considered in all children with spinal pain, lumbar nerve root symptoms, and an abnormal gait. As in adults, acute back pain is usually a self-limited musculoskeletal disorder that does not require investigation, and which responds to mobilization exercises and nonsteroidal anti-inflammatory medications. However, there are red flags that should trigger more aggressive evaluation. These include fever; pain that does not improve at night, at rest, or when supine; weight loss; known malignancy; or when symptoms extend beyond several weeks. See Box 12.4 for a list of differential diagnoses.