Peripheral Nerve Disorders

97 Peripheral Nerve Disorders







Perspective


Peripheral nerve disorders can result in varied findings, including proximal or distal weakness, symmetric or asymmetric symptoms, and acute or chronic manifestations. Motor symptoms range from weakness to paralysis, whereas sensory symptoms range from numbness to pain.


Evaluation of peripheral nerve disorders requires an understanding of the anatomy of the spinal cord and the peripheral nervous system (Fig. 97.1). The peripheral nervous system is composed of 12 cranial nerves and 31 spinal nerves. Spinal nerves are formed from motor fibers whose cell bodies reside in the ventral horn of the spinal cord and from sensory fibers whose cell bodies are found in the dorsal root ganglion. The motor and sensory fibers join to form one nerve as it exits the spinal canal. Spinal nerves from several spinal levels merge at the cervical, brachial, lumbar, and sacral plexuses. Peripheral nerves originate either at these plexuses or, if they are formed from nerves of only one spinal level, as they exit the vertebral foramina.



Peripheral nerves consist of mixed fibers with variable amounts of motor, sensory, and autonomic fibers; small and large fibers; and myelinated and unmyelinated fibers. These fibers, which are surrounded by endoneurial fluid and covered in perineurium, form fascicles that are bundled together by the epineurial sheath. This sheath forms a protective barrier akin to the blood-brain barrier in the central nervous system.


In patients with symptoms concerning for a peripheral nerve disorder, the history and physical examination are important in localizing the lesion. Spinal nerve, or nerve root, lesions are called radiculopathies and result in myotomal weakness or dermatomal sensory loss. Plexus lesions can be variable, with symptoms that cross myotomes and dermatomes or involve multiple peripheral nerves. Symptoms depend on which trunk or cord is involved. Peripheral nerve lesions cause weakness and sensory loss that is limited to a specific peripheral nerve.


Systemic diseases affect the peripheral nervous system as well, and multiple peripheral nerves may be involved. Examples include disorders of the neuromuscular junction (NMJ), demyelinating disorders, diabetes, and toxic effects of drugs or chemicals (Box 97.1).




Radiculopathies







Treatment


In the acute phase of injury, painful symptoms are typically treated conservatively with nonsteroidal antiinflammatory drugs (NSAIDs) and physical therapy. Low-quality evidence suggests that there is no difference between bed rest and activity for patients with sciatica.1 However, a randomized controlled trial showed that the addition of physical therapy is more effective than counseling and pain medications alone, although it may not be as cost-effective.2 Persistent or severe symptoms may require more invasive measures, from local corticosteroid injections to neurosurgical intervention.3 For the cervical spinal nerves, some evidence has shown that conservative therapy consisting of pain control has favorable short-term outcomes when compared with surgical intervention, although long-term outcomes appear to be similar.4 Surgical outcomes can be dependent on the mechanism of injury; for example, with spinal stenosis, 70% of patients will still have persistent loss of function. Chronic pain symptoms may be treated with medications used for neuropathic pain, such as antidepressants or anticonvulsants.



Mononeuropathies




Epidemiology


As with radiculopathy, compression of peripheral nerves is the most common cause of peripheral mononeuropathy, the most frequent being median mononeuropathy (Fig. 97.2). Women older than 55 years are most commonly affected, with a 4.6% prevalence in women and 2.8% in men.5 The second most frequent cause is ulnar mononeuropathy; specifically, cubital tunnel syndrome. Other common peripheral mononeuropathies include involvement of the radial nerve in the upper extremity and the peroneal and lateral cutaneous femoral nerves in the lower extremity.




Pathophysiology, Presenting Signs and Symptoms, and Diagnostic Testing


For mononeuropathies, the history and physical examination largely lead to the appropriate diagnosis. Findings in patients with common mononeuropathies and diagnostic maneuvers are presented in Table 97.2.612 In patients with a history of trauma or acute symptoms, plain films may be necessary to rule out fracture or dislocation. Patients with subacute or chronic symptoms should be asked about chronic conditions. Mononeuropathies can occur with several systemic diseases, including diabetes mellitus, amyloidosis, HIV, and states that cause edema, such as pregnancy.13 Outpatient testing may be more appropriate for individuals with chronic symptoms. MRI or electrodiagnostic testing such as electromyography or nerve conduction studies may be necessary, and the patient should be referred to a neurologist. MRI may demonstrate chronic nerve injury, whereas electrodiagnostic testing may show slowing of nerve conduction. These studies may aid in deciding whether surgical repair or decompression is necessary for certain syndromes.




Treatment


Primary treatment should be aimed at the precipitating event for both acute and chronic mononeuropathy.


With acute mononeuropathy, the primary cause of injury is generally trauma. Fractures and dislocations should be reduced appropriately and immobilized with the guidance of surgical consultation.


Initial treatment of chronic mononeuropathy is typically conservative and supportive. Modification of behavior is a key component of treatment and prevention of further injury. For carpal tunnel syndrome, behavior modification includes weight loss and avoidance of caffeine, nicotine, and alcohol. Patients should be instructed to decrease any possible trauma related to repetitive use by making changes in workplace ergonomics, reducing repetitive use, and changing posture. Some neuropathies may require supportive devices; for example, the carpal tunnel may benefit from wearing a wrist splint, the ulnar nerve from wearing a sling or a long arm posterior splint, the radial nerve from wearing a volar splint, and the peroneal nerve from wearing a posterior splint.8,9 NSAIDs are typically prescribed for relief of symptoms, although they may be ineffective without appropriate behavioral modification. In patients with a systemic disease, the primary process should be treated. Diuretics may be given if edema is believed to be contributing significantly to the patient’s symptoms. More invasive procedures, such as local nerve block for meralgia paresthetica or surgical decompression for carpal tunnel syndrome, are reserved for severe cases.



Autoimmune Disorders



Guillain-Barré Syndrome





Presenting Signs and Symptoms



Jun 14, 2016 | Posted by in EMERGENCY MEDICINE | Comments Off on Peripheral Nerve Disorders

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