Case 11

HISTORY AND PHYSICAL EXAMINATION

A 30-year-old right-handed man developed neck and left parascapular pain over 2 weeks. Two days before presentation, his pain worsened and he had a radiating pain to the posterior aspect of the arm and numbness of the hand, particularly the index and middle fingers. He became aware of weakness of the left arm. His pain was exacerbated by coughing and neck movement. He denied any history of trauma. He had a history of left parascapular pain that occurred 2 years earlier, which responded to nonsteroidal anti-inflammatory agents. Otherwise, he had been in excellent health.

On examination, the range of neck movements was restricted in all directions. Lateral neck flexion to the left reproduced the left parascapular and arm pain. There was no atrophy or fasciculations. He had moderate weakness of the left triceps muscle (Medical Research Council [MRC] grade 4/5) and very mild weakness of the left wrist extensors (MRC grade 5–/5). All other muscles were normal. The left triceps reflex was trace. All other reflexes were 2/4. Sensory examination revealed no objective sensory impairment. Examination of the right upper and both lower extremities revealed no abnormalities.

Cervical spine x-rays showed reversal of the normal cervical lordosis with normal disk interspaces. Initially, the patient was treated conservatively with cervical traction, nonsteroidal anti-inflammatory agents, and analgesia. Ten days later, there was no improvement.

An electromyography (EMG) examination was then performed.

Please now review the Nerve Conduction Studies and Needle EMG tables.

EDX FINDINGS AND INTERPRETATION OF DATA

Pertinent electrodiagnostic (EDX) findings in this case include:

1. Normal sensory nerve action potentials (SNAPs), particularly those pertinent to C6 and C7 dermatomes (median SNAP recording thumb, index, and middle fingers, and radial SNAP).

2. Variably increased insertional activity, fibrillation potentials, and decrease in recruitment in the pronator teres (C6, C7), flexor carpi radialis (C6, C7), triceps (C6, C7, C8), and extensor carpi radialis (C6, C7), with normal biceps (C5, C6), brachioradialis (C5, C6), and deltoid (C5, C6). The abnormal muscles are innervated by two different nerves (median and radial), but they all share C7 root innervation. Also, muscles that share C6 but not C7 myotomes are normal.

3. Decreased recruitment of motor unit action potential (MUAP), and minimal reinnervation changes of the MUAPs are findings consistent with a subacute disorder.

4. Fibrillation potentials in the low cervical paraspinal region.

Case 11: Nerve Conduction Studies

Case 11: Needle EMG

These findings are compatible with a subacute left C7 radiculopathy with active denervation. Normal SNAPs and fibrillation potentials in the cervical paraspinal muscles confirm that the lesion is proximal to the dorsal root ganglion (DRG), i.e., within the intraspinal canal.

DISCUSSION

Applied Anatomy

The dorsal root axons originate from the sensory neurons of the DRG, which lie outside the spinal canal, within the intervertebral foramen, immediately before the junction of the dorsal and ventral roots (Figure C11-1). These sensory neurons are unique because they are unipolar. They have proximal projections through the dorsal root, called the preganglionic sensory fibers, to the dorsal horn and column of the spinal cord. The distal projections of these neurons, called the postganglionic peripheral sensory fibers, pass through the spinal nerve to their respective sensory end-organs. The ventral root axons, however, are mainly motor (some are sympathetic, with origins from the anterolateral horn of the cord). The motor axons originate from the anterior horn cells within the spinal cord. Passing through the spinal nerves and the peripheral nerve, these motor fibers terminate in the corresponding muscles.

Figure C11-1 Transverse section of the cervical spine, showing the usual site of root injury in cervical radiculopathy due to disc herniation (arrow). Note that the sensory fibers are injured proximal to the dorsal root ganglion, which is located within the intervertebral foramen.

(From Brown WF, Bolton CF. Clinical electromyography, 2nd ed. Boston, MA: Butterworth-Heinemann, 1993, with permission.)

The spinal nerves terminate as soon as they exit the intervertebral foramina, by branching into posterior and anterior rami. The small posterior rami innervate the paravertebral skin and deep paraspinal muscles of the neck, trunk, and back; the large anterior rami innervate the skin and muscles of the trunk and limbs.

In humans, there are 31 pairs of spinal nerve roots: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal. In the cervical spine, each cervical root exits above the corresponding vertebra that shares the same numeric designation (Figure C11-2). For example, the C5 root exits above the C5 vertebra (i.e., between the C4 and C5 vertebrae). Because there are seven cervical vertebrae but eight cervical roots, the C8 root exits between the C7 and T1 vertebrae; subsequently, all thoracic, lumbar, and sacral roots exit below their corresponding vertebrae. For example, the L3 root exits below the L3 vertebra (i.e., between the L3 and L4 vertebrae).

Figure C11-2 Alignments of spinal segments and roots to vertebrae. The bodies and spinal processes of the vertebrae are indicated by Roman numerals, and the spinal segments and their respective roots by Arabic numerals. Note that the cervical roots (except C8) exit through intervertebral foramina above their respective bodies and that all other roots leave below these bodies.

(From Haymaker W, Woodhall B. Peripheral nerve injuries: principles of diagnosis. Philadelphia, PA: WB Saunders, 1953, with permission.)

Clinical Features

Cervical radiculopathy frequently is the result of a herniated intervertebral disc, or osteophytic spondylitic changes that result in mechanical compression of the cervical root. The symptoms may be acute, subacute, or chronic. Neck pain radiating to the parascapular area and upper extremity, made worse by certain neck positions, is common. The pain radiation tends to follow the dermatomal innervation of the compressed root. Subjective paresthesias within the involved dermatome is more common than objective sensory findings. The diminution of deep tendon reflexes helps in localizing the lesion to one or two roots. Weakness is uncommon; when present, it involves muscles innervated by the compressed root.

The classic study by Yoss et al., published in 1957, remains the best available clinicoanatomic study of cervical root compression. This detailed study analyzed the symptoms and signs of 100 patients with surgically proven single cervical lesions. C7 radiculopathy was the most common cervical radiculopathy, accounting for almost two thirds of patients (Figure C11-3). Figure C11-4 shows the common sensory symptoms and signs observed in these patients, while Figure C11-5 shows the weakened muscles caused by cervical radiculopathy. This study revealed the extreme variability of sensory manifestations in patients with cervical radiculopathy. Also, no single muscle was exclusively diagnostic of a specific root compression. However, based on the data, certain clinical conclusions can be made:

1. When sensory manifestations occur in C7 radiculopathy, the index or middle finger is always involved.

2. When sensory manifestations occur in C8 radiculopathy, the little or ring finger is always involved.

3. The thumb is never involved exclusively in C7 radiculopathy.

4. Significant triceps weakness is seen only in C7 radiculopathy.

5. Significant supraspinatus and infraspinatus weakness is seen only in C5 radiculopathy.

6. Significant interossei and hand intrinsics weakness is seen only in C8 radiculopathy.

Figure C11-3 Incidence of cervical root involvement in a series of 100 patients with surgically proven single-level lesions.

(Data adapted from Yoss RE et al. Significance of symptoms and signs in localization of involved root in cervical disc protrusion. Neurology 1957;7:673–683, with permission.)

Figure C11-4 Sensory manifestation in patients with established single cervical root lesions (C5–C8). (A) patterns of paresthesias in 91 patients and (B) objective sensory impairment in 23 of the same patients.

(From Yoss RE et al. Significance of symptoms and signs in localization of involved root in cervical disc protrusion. Neurology 1957;7:673–683, with permission.)

Figure C11-5 Incidence and severity of weakness of muscles or groups of muscles in cervical radiculopathy (C5–C8).

Rights were not granted to include this figure in electronic media. Please refer to the printed book.

(From Yoss RE et al. Significance of symptoms and signs in localization of involved root in cervical disc protrusion. Neurology 1957;7:673–683, with permission.)

However, despite the variability in sensory and motor presentations of cervical radiculopathies, certain classical symptoms and signs exist and are extremely helpful in localizing the compressed root. Table C11-1 reveals the common presentations of cervical radiculopathies.

Table C11-1 Common Clinical Presentations in Patients With Cervical Radiculopathies