Veda V. Vedanarayanan, MD, FRCPC
CHAPTER CONTENTS
◦Acute Inflammatory Demyelinating Polyneuropathy
◦Acute-Onset Chronic Inflammatory Demyelinating Polyneuropathy
◦Chronic Inflammatory Demyelinating Polyneuropathy
◦Diabetic Lumbosacral Plexopathy
◦Hereditary Neuropathy with Pressure Palsies
◦Lambert Eaton Myasthenic Syndrome
◦Muscles, Weakness, and Laboratory Studies
◦Critical Illness Neuromyopathy
◦Metabolic and Endocrine Myopathies
◦Amyotrophic Lateral Sclerosis
OVERVIEW
Neuromuscular disorders may be encountered as known chronic conditions that are exacerbated by a hospital stay, be the principal reason for admission, or develop during a prolonged hospitalization.
PERIPHERAL NERVE
Acute Inflammatory Demyelinating Polyneuropathy
Acute inflammatory demyelinating polyneuropathy (AIDP) or Guillain-Barré syndrome (GBS) is an immune-mediated peripheral neuropathy with an acute to subacute, monophasic course that typically reaches maximal symptomatology at 3–4 weeks. Most cases present as an inflammatory demyelinating pathology; however, axonal variants do exist.
AIDP is often associated with a preceding illness. The most common are:
•Upper respiratory tract infections
PRESENTATION is typically with progressive generalized weakness, which at times leads to respiratory compromise and dysautonomia. Weakness usually starts in the lower extremities; however, some cases will begin in the upper extremities or all four extremities simultaneously. Most patients will present with reduced or absent reflexes; however, reflexes may be preserved for several days after onset. Severe cases can progress to respiratory insufficiency necessitating ventilatory support. Dysautonomia is common especially with severe disease.
DIAGNOSIS is suspected with progressive weakness and especially with associated reduced or absent tendon reflexes.
•Brain and spine imaging are unrevealing and often not necessary. However, if CNS demyelination or primary spinal cord pathology is considered, magnetic resonance imaging (MRI) of the brain and/or spinal cord may be needed.
•Electromyography and nerve conduction studies (EMG/NCS) typically show evidence of demyelinating features, including prolongation or absence of F-waves, reduced velocities, and evidence of temporal dispersion when viewing the compound motor action potential (CMAP) wave forms. Very early in the course, EMG/NCS studies might be normal. Prolonged or absent late responses (F-waves and/or H-reflexes) are the earliest finding on electrodiagnostic testing.
•CSF findings include albuminocytologic dissociation—elevation in CSF protein without an elevation in CSF WBC. However, elevation in the CSF WBC can be seen in patients with AIDP associated with HIV. There can be a delay in the elevation of protein of up to 2 weeks. Therefore, if there remains a clinical question, repeat CSF examination may be warranted.
MANAGEMENT usually begins with hospital admission; patients who are diagnosed with AIDP should be maintained in the hospital for close monitoring until it has been determined that the course of the disease has reached a plateau or has begun to improve. Weakness can progress rapidly, leading to profound paralysis, respiratory insufficiency, and/or autonomic dysfunction with cardiovascular complications requiring emergency intervention. Telemetry is recommended.
•ICU monitoring should be considered for all patients with any signs of respiratory distress, a forced vital capacity of less than 20 mL/kg, severe bulbar palsy, or significant dysautonomia.
•General medical care includes deep vein thrombosis (DVT) prophylaxis; monitoring for infection and skin breakdown, especially in those with severe motor dysfunction; nutritional support; and regular bowel care to prevent the development of an adynamic ileus.
•Immunotherapy: Plasmapheresis or IV immunoglobulin (IVIg) can be used in patients with AIDP. Immunotherapy shortens the recovery time and lessens long-term disability. There is no evidence that one treatment modality is superior to the other. Decisions on which therapy to pursue depend on concomitant medical issues, contraindications, availability at the treating facility, and patient preference. Corticosteroids have been shown to not be effective in AIDP and should not be used. Typical dosing for IVIg is 0.4 g/kg/day for 3–5 days. Plasma exchange is typically carried out for a total of 3–5 exchanges.1
•Pain: Patients typically may develop fairly severe neuropathic pain. Typical neuropathic pain medications including gabapentin, pregabalin, duloxetine, or tricyclic antidepressants can be beneficial.
•Therapy: Involvement of occupational and physical therapy early in the course can also hasten recovery. Speech therapy is also warranted, especially in those with significant bulbar symptoms, to promote safe swallowing.
•Autonomic involvement: Along with respiratory compromise, autonomic dysfunction in AIDP can be life-threatening. Patients should be monitored closely so life support measures can be put in place if needed. Autonomic dysfunction is seen more often in the demyelinating forms than in the axonal variants. Autonomic changes can be:
◦Anhydrosis and/or diaphoresis
•Hyponatremia can be seen in AIDP and is usually due to the syndrome of inappropriate antidiuretic hormone (SIADH) and natriuresis. The treatment differs; both require replenishment of sodium but SIADH needs fluid restriction, and, natriuresis requires intravascular volume expansion.2
Axonal Variants
Axonal variants are less common in Western countries than demyelinating forms. Axonal types are more often seen in Asian populations.
Acute motor axonal neuropathy (AMAN) is often preceded by Campylobacter jejuni infection. Presenting clinical features and overall disease progression are very similar to AIDP. Since this is predominantly axonal, reflexes can be preserved. Electrodiagnostic testing shows axonal changes rather than prominent demyelination.
Acute motor and sensory axonal neuropathy (AMSAN) is a more severe variant of AIDP. It is characterized by involvement of both sensory and motor fibers with significant axonal degeneration. Recovery is often delayed or incomplete. Electrodiagnostic testing reveals involvement of both motor and sensory responses with denervation noted on needle electromyogram (EMG).
Acute-Onset Chronic Inflammatory Demyelinating Polyneuropathy
Acute-onset chronic inflammatory demyelinating polyneuropathy (A-CIDP) presents similarly to AIDP. This is CIDP but with a more rapid onset. Approximately 16% of patients with CIDP present acutely.3
PRESENTATION is with typical AIDP initially, then there is regression after initial improvement with immunotherapy.
DIAGNOSIS is suspected when a patient with AIDP has worsening after initial response to therapy. Differentiating AIDP from A-CIDP is important because those with A-CIDP variant will require continued long-term treatments.
Patients with A-CIDP are more likely to have the following features:
Patients who did not progress to A-CIDP are more likely to have the following features:
•Identified antecedent illness
MANAGEMENT of A-CIDP is as for CIDP.
Chronic Inflammatory Demyelinating Polyneuropathy
CIDP is a demyelinating neuropathy similar to AIDP but with a more protracted course. Patients have a progressive course over more than 4 weeks.
PRESENTATION is with weakness and sensory deficit with decreased or absent reflexes. There is usually no identified antecedent illness. Autonomic and respiratory difficulties are not expected. Cranial nerve abnormalities are uncommon.
DIAGNOSIS is suspected in a patient with progressive weakness and sensory disturbance and reduced or absent reflexes.
•Imaging of the brain and spine is unremarkable and seldom needed.
•CSF shows findings similar to AIDP with increased protein and no increase in WBC.
•NCS shows demyelinating polyneuropathy. Multifocal conduction block is strongly supportive of the diagnosis.
•EMG shows no denervation early in the course. Late in the course, denervation may be seen in a minority of patients.
MANAGEMENT is similar to AIDP with response to IVIg or plasma exchange. In addition, corticosteroids are effective for CIDP whereas they are not for AIDP. Patients often respond best to one treatment, so if there is no response to a particular modality, one of the others should be considered. Treatment options include the following:
•Prednisone is often given at 60–80 mg/day for several weeks then tapered as tolerated. While this is effective and used first-line by many clinicians, the deleterious effects of long-term corticosteroids are of concern.
•IVIg is an excellent alternative to prednisone and used as first-line treatment by some, especially if comorbid conditions make corticosteroid treatment risky (e.g., diabetes). Initial treatment is usually for 3–5 days, but follow-up doses are needed at intervals dictated by response and relapse.
•Plasma exchange is effective and is comparable to prednisone and IVIg in response rate, but because of the logistics of performing plasma exchange (frequency and duration of treatments, vascular access) this is seldom used first-line for CIDP.
Multifocal Motor Neuropathy
Multifocal motor neuropathy (MMN) is an inflammatory demyelination restricted to motor nerves. In other respects, it is similar to CIDP.
PRESENTATION is with progressive weakness, often starting in one limb but then becoming more extensive. Although this is not a motoneuron degeneration, fasciculations can occur, but since the motoneurons are relatively preserved, there is not the marked atrophy of amyotrophic lateral sclerosis (ALS).
DIAGNOSIS is suspected with progressive weakness without corticospinal tract signs. EMG and NCS show conduction block. Anti-GM1 antibodies can be seen.
MANAGEMENT is most commonly with IVIg. Cyclophosphamide is also used.
Mononeuropathies
Most mononeuropathies are diagnosed in the outpatient setting, but some acute presentations may be encountered in the hospital. Some of the important mononeuropathy scenarios are as follows:
Radial neuropathy: Compression produces weakness of the wrist and finger extensors with resultant wrist drop. Triceps weakness may be seen. This presentation may trigger admission because of concern over monoplegia from stroke. Without careful exam, wrist instability may give the perception of finger flexor weakness, whereas with stabilization of the wrist, full strength of median- and ulnar-innervated muscles can be demonstrated. Classically, this is seen in alcoholics who become somnolent while resting their arm in a position vulnerable to radial palsy.
Peroneal neuropathy: Weakness of the tibialis anterior is most prominent, producing deficit in foot dorsiflexion. This can be hospital-acquired since the peroneal nerve is susceptible to compression at the fibular neck, making prolonged bedrest a risk for peroneal palsy. The lesion may be higher because if the sciatic nerve is compressed, the peroneal division seems more susceptible to compression damage.
Sciatic neuropathy: Weakness of the peroneal or tibial divisions can produce deficits in foot dorsiflexion or plantar flexion and may additionally affect the knee flexors. Potential causes of damage include hip or knee fractures or surgery, pelvic fractures, and, less likely, injections.
Femoral neuropathy: Weakness of the knee extensors is most evident. Common causes include pelvic surgery and bleeding into the region of the nerve or plexus (e.g., from surgery or arterial puncture).
Diabetic amyotrophy: Damage to the lumbosacral plexus from diabetes produces pain and weakness most prominent in the quadriceps but also involving other L2–L3 innervated muscles. Superimposed polyneuropathy may produce deficits beyond this distribution. This may trigger hospitalization because of concern over possible stroke, especially anterior cerebral artery infarction, which can produce unilateral leg weakness without arm involvement. Proximal distribution of the deficits and regional pain support the correct clinical diagnosis.
Ulnar neuropathy: Intrinsic weakness of the hand from ulnar neuropathy is common in diabetics but is unlikely to trigger hospital admission or consultation.
Median neuropathy: Deficits of hand function from lesions of the median nerve at the wrist (carpal tunnel syndrome) or higher are uncommon in hospital practice. Diagnosis is assisted by careful examination of median-, ulnar-, and radial-innervated muscles to distinguish median neuropathy from a central lesion.
Herpes zoster and post-herpetic neuralgia: Reactivation of the varicella zoster virus produces pain in a single nerve root distribution and is associated with vesicular rash. This can be followed by prolonged neuropathic pain. This is discussed in Chapter 17.
Idiopathic Brachial Plexitis
Idiopathic brachial plexitis or neurogenic amyotrophy (also known as Parsonage-Turner syndrome) is an idiopathic attack on the brachial plexus. This is often believed to be an inflammatory autoimmune process that presents in a multifocal distribution. Neurogenic amyotrophy is often used as a preferred term because it is not clear that the pathology is consistently in the plexus.
PRESENTATION typically is with a fairly acute onset of pain in the shoulder then weakness and numbness in the shoulder girdle and arm. The weakness can be remarkably focal. Most patients experience a plateau of symptoms fairly quickly, with a slow resolution.
DIAGNOSIS is suggested by rapid onset of shoulder pain and arm weakness that does not fall into one radicular distribution. Electrodiagnostic studies may often be normal initially due to the acute onset. CSF may show a mild pleocytosis. Differential diagnosis includes an acute radiculopathy or a traumatic injury to the shoulder and/or brachial plexus.
MANAGEMENT includes physical therapy along with symptomatic neuropathic pain therapies.
Diabetic Lumbosacral Plexopathy
Diabetic lumbosacral plexopathy or diabetic amyotrophy is a lumbar radiculoplexopathy affecting the lower extremity.
PRESENTATION is with pain in the back, hip, and upper leg. Weakness develops in proximal muscles, particularly quadriceps and iliopsoas. Symptoms often develop after an epoch of significant weight loss.
DIAGNOSIS is suspected with proximal pain and weakness in a patient with known diabetes. Hgb A1C is often measured to assess diabetic control. MRI of the lumbar spine and plexus can look for structural causes of plexopathy. EMG may show denervation, especially in these proximal muscles and additionally often shows a coexistent peripheral neuropathy.
MANAGEMENT begins with optimal glucose control. Physical therapy is helpful. No medications have become standard therapy; there is some evidence for immunotherapy, but this is not proved and not recommended for most patients.4
Mononeuritis Multiplex
Mononeuritis multiplex is dysfunction of multiple individual nerves. The most common cause is diabetes. There are many other causes including polyarteritis nodosa, sarcoidosis, Lyme disease, HIV, Wegener granulomatosis, and hereditary neuropathy with liability to pressure palsies.
PRESENTATION is with deficits affecting multiple individual nerves, typically asymmetric. Almost any nerve can be affected. Typical findings include wrist drop, foot drop, and/or a cranial neuropathy.
DIAGNOSIS is suspected with asymmetric individual peripheral nerve deficits (e.g., ulnar and peroneal).
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