Peripheral Neuropathies

Guillain-Barré syndrome (GBS), once thought to be a single disease process, is a family of immune-mediated polyneuropathies that occur after infections (e.g., with Campylobacter jejuni). Typical GBS is characterized by acute monophasic neuromuscular paralysis, which is symmetric and ascending in progression. If the paralysis reaches the respiratory muscles, GBS can progress into respiratory failure, which requires prolonged hospitalization. Management is mostly supportive and may require either plasma exchange or IV immunoglobulin.

A neurological exam is a systematic assessment of cognitive, sensory, and motor responses to identify pathologies of the nervous system. A neurological exam allows for the localization of neurologic lesions to narrow the differential diagnosis and focus on subsequent laboratory and imaging examinations. The exam should include assessments of the subject's mental status, speech, cranial nerves, motor system, deep tendon reflexes, sensation, balance, and coordination.

There are many etiologies of peripheral nerve injuries in the cervicothoracic region. The injuries commonly involve the phrenic nerve, the suprascapular nerve, the dorsal scapular nerve, the long thoracic nerve, or the thoracodorsal nerve. The nerves arise from the cervical plexus and brachial plexus. Causes of injury vary and may include trauma, compression, nerve entrapment, stretch or traction from repetitive movement, infection, surgical injury, or metabolic causes. Clinical presentation depends upon the motor and sensory innervation of the affected nerves. Diagnosis is mostly clinical but may also be confirmed with imaging or electrodiagnostic studies. Depending on the specific injury, management may be either surgical or conservative (physical therapy and avoidance of precipitating movements).

Diabetes mellitus (DM) is a chronic metabolic disorder characterized by persistent hyperglycemia due to impaired insulin secretion (type 1 DM), insulin resistance (type 2 DM), or both (latent autoimmune diabetes in adults (LADA)). The goal of diabetes management is to prevent chronic serious and potentially disabling complications due to damage to various organs. Adequate long-term control of blood glucose is crucial in the prevention of complications. Macrovascular complications include heart disease, stroke, peripheral vascular disease, and CKD in various stages, including end-stage renal disease that requires dialysis. Microvascular disease can cause retinopathy, neuropathy, or symptomatic cardiac disease, which are not seen during stress testing or angiogram that are used to diagnose large vessel diseases.

Glucocorticoids are a class within the corticosteroid family. Glucocorticoids are chemically and functionally similar to endogenous cortisol. There are a wide array of indications, which primarily benefit from the antiinflammatory and immunosuppressive effects of this class of drugs. These medications are also used for conditions requiring physiologic glucocorticoid replacement. Despite their extensive use, glucocorticoids can produce many and varied adverse effects and should be used judiciously. Because of their immunosuppressive effect, these medications may predispose individuals to infection and should be avoided in those with uncontrolled infections. In addition, long-term therapy can lead to suppression of the hypothalamic-pituitary-adrenal (HPA) axis, so discontinuation of therapy should be done carefully to avoid adrenal insufficiency.

Polyneuropathy is any disease process affecting the function of or causing damage to multiple nerves of the peripheral nervous system. There are numerous etiologies of polyneuropathy, most of which are systemic and the most common of which is diabetic neuropathy. The clinical presentation varies by etiology as well as classification of the polyneuropathy, but generally manifests as sensorimotor disturbances (pain, paresthesia, numbness, weakness, and loss of coordination and balance), which have a gradual onset and progressive course. Distal nerves are affected most commonly, but the disease process may progress proximally with time or progression of the underlying etiologic disease entity. Diagnosis is made clinically, but laboratory studies, electrodiagnostic testing, and/or nerve biopsy may be required in some cases. Management varies depending on the etiology.

Peripheral nerve damage affecting the upper extremities is a common occupational injury and also occurs in individuals who participate in recreational sports. Injuries can affect the axillary, musculocutaneous, median, ulnar, or radial nerves. The most common causes of these injuries are overuse, compression or entrapment, or nerve trauma; degenerative or demyelinating disorders; radiation therapy; and mass lesions. Clinical presentation is with motor and/or sensory deficits. Diagnosis is made clinically and based on electrodiagnostic and imaging studies. Treatment in most cases is conservative, although surgical intervention may occasionally be necessary.

Carpal tunnel syndrome (CTS) is a complex of signs and symptoms caused by compression of the median nerve as it crosses the carpal tunnel. Presentation is with pain and paresthesia of the dermatomal target tissues innervated by the median nerve as well as weakness and atrophy of the nerve's myotomal targets. Risk factors that cause a predisposition to CTS include obesity, female sex, pregnancy, diabetes, inflammatory conditions, genetic predisposition, and occupational factors. A clinical diagnosis may be made on the basis of history and physical examination and confirmed with electrodiagnostic testing. Conservative management includes splinting and physical therapy; more severe cases may require surgical correction.

Guillain-Barré syndrome (GBS), once thought to be a single disease process, is a family of immune-mediated polyneuropathies that occur after infections (e.g., with Campylobacter jejuni). Typical GBS is characterized by acute monophasic neuromuscular paralysis, which is symmetric and ascending in progression. If the paralysis reaches the respiratory muscles, GBS can progress into respiratory failure, which requires prolonged hospitalization. Management is mostly supportive and may require either plasma exchange or IV immunoglobulin.

Paraneoplastic syndromes are a heterogeneous group of disorders caused by an abnormal immune response to a neoplasm. The substances produced are not due to the direct effect of the tumor, such as metastasis, mass effect, or invasion. Antibodies, hormones, cytokines, and other substances are generated and affect multiple organ systems. About 10% of cases of cancer are affected by paraneoplastic syndromes. The common cancers that present with paraneoplastic syndromes include cancer of the lung, breast, ovaries, kidney, liver, and stomach and lymphomas.

The junction between 2 neurons is called a synapse. The synapse allows a neuron to pass an electrical or chemical signal to another neuron or target effector cell. The neuron that sends the signal to another neuron is called the presynaptic neuron, while the neuron that receives the signal is called the postsynaptic neuron. The plasma membranes of the 2 neurons are placed very close together and are held in place by synaptic adhesion molecules that proceed from both the presynaptic and postsynaptic neurons. The space between the 2 neurons is called the synaptic cleft. The molecules that mediate the interaction are called neurotransmitters.

Upper motor neurons (UMNs) and lower motor neurons (LMNs) combine to form a neuronal circuit for movement. UMNs are responsible for carrying motor information from the cerebral cortex and brain stem to the spinal cord, and LMNs carry motor information from UMNs in the spinal cord to the skeletal muscles for movement. Upper motor neuron lesions cause damage to neurons above the motor nuclei of the cranial nerves in the brain stem or the anterior horn cells in the spinal cord. These lesions present clinically with symptoms of weakness, spasticity, clonus, and hyperreflexia. Causes include stroke, traumatic brain injury, brain cancer, infectious and inflammatory disorders, and metabolic and neurodegenerative disorders. Lower motor neuron lesions affect the nerve fibers traveling from the anterior horn of the spinal cord to the peripheral muscle. These lesions present clinically with muscle weakness, atrophy, and hyporeflexia, with sensation remaining intact. Diagnosis is made by clinical neurologic exam, and management is mostly supportive, but some newer therapies have recently become available.

The forearm is the region of the upper limb between the elbow and the wrist. The term “forearm” is used in anatomy to distinguish this area from the arm, a term that is commonly used to describe the entire upper limb. The forearm consists of 2 long bones (the radius and the ulna), the interosseous membrane, and multiple arteries, nerves, and muscles. The muscles are grouped into 2 compartments: anterior and posterior. The function of these muscles is flexion and extension of the wrist and fingers, while also contributing to flexion of the elbow.