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Monoplegia
Weakness or paralysis of a limb is usually due to pathology of the spine and the proximal portion of nerves. Monoplegia may also be the initial presentation of a hemiplegia, paraplegia, or quadriplegia. Therefore one must also consult the differential diagnosis of spinal paraplegia provided in Box 12.1 and the table and boxes in Chapter 11 referring to the differential diagnosis of cerebral hemiplegia.
Approach to monoplegia
Either pain or weakness may cause refusal to use a limb. The cause of most painful limbs is orthopedic or rheumatological (arthritis, infection, and tumor). A trivial pull on an infant’s arm may dislocate the radial head and cause an apparent monoplegia. Pain followed by weakness is a feature of plexitis.
Box 13.1 summarizes the differential diagnosis of acute monoplegia. Plexopathies and neuropathies are the leading causes of pure monoplegia. Stroke often affects one limb more than others, usually the arm more than the leg. The presentation may suggest monoplegia, but careful examination often reveals increased tendon reflexes and an extensor plantar response in the seemingly unaffected limb. Any suggestion of hemiplegia rather than monoplegia, or increased tendon reflexes in the paretic limb, should focus attention on the brain and cervical cord as the pathological site.
Box 13.1
Differential Diagnosis of Acute Monoplegia
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Complicated migraine a
a Denotes the most common conditions and the ones with disease modifying treatments
(see Chapter 11 )
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Dislocation of the radial head
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Hemiparetic seizures a (see Chapter 11 )
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Monomelic spinal muscular atrophy
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Plexopathy and neuropathy
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Acute neuritis
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Hereditary
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Hereditary brachial neuritis
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Hereditary neuropathy with liability to pressure palsy
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Injury
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Lacerations
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Pressure injuries
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Traction injuries a
- ▪
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Stroke (see Box 11.2 )
Chronic, progressive brachial monoplegia is uncommon. When it occurs, one should suspect syringomyelia and tumors of the cervical cord or brachial plexus. Chronic, progressive weakness of one leg suggests a tumor of the spinal cord or a neurofibroma of the lumbar plexus. A monomelic form of spinal muscular atrophy, affecting only one leg or one arm, should be considered when progressive weakness is unaccompanied by sensory loss.
Spinal muscular atrophies
The first report of a monomelic form of spinal muscular atrophy was from Asia but the condition is probably equally common among Europeans. The terms used to describe the entity are benign focal amyotrophy and monomelic amyotrophy . While trauma and immobilization of the limb may precede the onset of atrophy by several months, a cause-and-effect relationship is not established.
A genetic cause is not firmly established, as less than 1% of patients have a family history. When the disease is familial, the transmission is by autosomal recessive inheritance. Two affected brothers had a mutation in the superoxide dismutase 1 gene. In one set of male identical twins, both developed atrophy of first one hand and then the other.
Clinical features
Onset is usually in the second or third decade and has a male preponderance. The initial features are usually weakness and atrophy in one limb, the arm in 75% and the leg in 25% of cases. Tendon reflexes in the involved limb are hypoactive or absent. Sensation is normal. The weakness and atrophy affect only one limb in half of cases and spread to the contralateral limb in the remainder. Tremor of one or both hands is often associated with wasting. The appearance of fasciculations heralds weakness and atrophy. Progression is slow, and spontaneous arrest within 5 years is the rule. However, another limb may become weak after a gap of 15 years.
Diagnosis
Needle electromyography (EMG) studies of all limbs are essential to show the extent of involvement. The studies are often normal at onset and show a denervation pattern 3–4 weeks later. Motor conduction is normal. Magnetic resonance imaging (MRI) of the spine and plexus is required to exclude a tumor.
Management
Physical therapy, occupational therapy, splinting, and bracing are the main supportive treatment options.
Plexopathies
Acute Idiopathic Plexitis
Acute plexitis is a demyelinating disorder of the brachial or lumbar plexus thought to be immune mediated. Brachial plexitis is far more common than lumbar plexitis.
Brachial Plexitis
Brachial plexitis ( brachial neuritis , neuralgic amyotrophy ) occurs from infancy to adult life. Prior tetanus toxoid immunization has occurred in 10%–20% of childhood and adult cases and in almost all infants. The site of immunization does not correlate with the limb involved. Cases may occur after seemingly mild upper respiratory infections, and symptoms may overlap with asthmatic amyotrophy (described later in this chapter).
Clinical features
The onset of symptoms is usually explosive. Pain is the initial feature in 95% of patients. Pain localization is to the shoulder but may be more diffuse or limited to the lower arm, and tends to be severe. It may awaken the patient, and the description is “sharp, stabbing, throbbing, or aching.” The duration of pain, which is frequently constant, varies from several hours to 3 weeks. As the pain subsides, weakness appears. Weakness is in the distribution of the upper plexus alone in half of patients and the entire plexus in most of the rest. Lower plexitis alone is unusual. Although the initial pain abates, paresthesias may accompany the weakness. Two-thirds of people report improved strength during the month after onset. Upper plexus palsies improve faster than do lower plexus palsies. Among all patients, one-third recover within 1 year, three-quarters by 2 years, and 90% by 3 years. After 3 years, further improvement may occur but permanent residua are expected. Recurrences are unusual and less severe than the initial episode.
Diagnosis
Pain and weakness in one arm are also symptoms of spinal cord compression, indicating the need for spinal cord imaging studies. However, when the onset is characteristic of brachial plexus neuritis, the clinical features alone establish the diagnosis. Diagnostic tests are not essential. The cerebrospinal fluid is usually normal. A slight lymphocytosis and mild elevation in protein content are sometimes noted. EMG and nerve conduction studies are helpful in showing the extent of plexopathy. Electrical evidence of bilateral involvement may be present in patients with unilateral symptoms.
Management
Gabapentin between 20 and 60 mg/kg/day divided into three or four doses, and pregabalin, a more effective choice, at 3–10 mg/kg/day divided into two doses, are helpful in controlling neuropathic pain but not the paresthesias or weakness associated with the plexopathy. Corticosteroids do not affect the outcome. Recommend range of motion exercises until strength recovers and occupational therapy to deal with any possible deficit. Keep the affected arm in a sling to avoid traction injuries.
Lumbar Plexitis
Lumbar plexitis occurs at all ages and is similar to brachial plexitis, except that it affects the leg instead of the arm. The mechanism is probably the same as in brachial plexitis.
Clinical features
Fever is often the first symptom as well as pain in one or both legs. The pain has an abrupt onset and may occur in a femoral or sciatic distribution. Sciatica, when present, suggests disk disease. Young children refuse to stand or walk, and older children limp. Weakness may develop concurrently with pain or be delayed for as long as 3 weeks. The onset of weakness is insidious and often difficult to date, but usually it begins 8 days after the onset of pain. Weakness progresses for a week and then stabilizes. Tendon reflexes are absent in the affected leg but are present in other limbs.
Recovery is characterized first by abatement of pain and then by increasing strength. The average time from onset of pain to maximal recovery is 18 weeks, with a range of 8 weeks to several years. Functional recovery is almost universal, but mild weakness may persist.
Diagnosis
The sudden onset of pain and weakness in one leg suggests spinal cord or disk disease. MRI of the spine is a means of excluding other disorders; the results are invariably normal in lumbar plexitis. The cerebrospinal fluid is normal except for a mild elevation of the protein concentration. EMG performed 3 weeks after onset shows patchy denervation.
Management
Gabapentin between 20 and 60 mg/kg/day divided into three or four doses, and pregabalin, a more effective choice, 3–10 mg/kg/day divided into two doses, are helpful in controlling the neuropathic pain but not the paresthesias or weakness associated with the plexopathy. Corticosteroids do not affect the outcome. Recommend range of motion exercises until strength recovers and occupational therapy to deal with any possible deficit.
Acute Symptomatic Plexitis
Asthmatic Amyotrophy (Hopkins Syndrome)
Sudden flaccid paralysis of one or more limbs, resembling poliomyelitis, may occur during recovery from an asthmatic attack. All affected children had previously received poliomyelitis vaccine. The etiological mechanism for this syndrome is unknown. Infection by a neurotropic virus other than poliovirus is a possibility. Adenovirus, echovirus, and coxsackievirus have been isolated from stool, throat, or cerebrospinal fluid in some cases. A recent case report suggests a possible atopic myelitis.
Clinical features
Age at onset is from 1–11 years, and the male-to-female ratio is 7:4. The interval between the asthmatic attack and the paralysis is 1–11 days, with an average of 5 days. Monoplegia occurs in 90% of cases, with the arm involved twice as often as the leg. The other 10% have hemiplegia or diplegia. Meningeal irritation is not present. Sensation is intact, but the paralyzed limb is painful in half of cases. Recovery is incomplete, and all affected children have some degree of permanent paralysis.
Diagnosis
Asthmatic amyotrophy is primarily a clinical diagnosis based on the sequence of events. The diagnosis requires distinction from paralytic poliomyelitis and idiopathic brachial neuritis. The basis for excluding paralytic poliomyelitis is normal cerebrospinal fluid in asthmatic amyotrophy. A few white blood cells may be present in the cerebrospinal fluid but never to the extent encountered in poliomyelitis, and the protein concentration is normal. EMG during the acute phase shows active denervation of the paralyzed limb, but the pattern of denervation does not follow the radicular distribution expected in a brachial neuritis.
Management
Gabapentin and pregabalin may be helpful in controlling neuropathic pain. Other analgesia may be needed. As with plexitis, physical and occupational therapy are often required.
Hereditary Brachial Plexopathy
The two major phenotypes of focal familial recurrent neuropathy are hereditary brachial plexopathy (also called hereditary neuralgic amyotrophy ) and hereditary neuropathy with liability to pressure palsies (see section on Mononeuropathies later in this chapter). The phenotypes can be confused because isolated nerve palsies may occur in hereditary brachial plexopathy, and brachial plexopathy occurs in patients with hereditary neuropathy with a liability to pressure palsies. Transmission of both disorders is by autosomal dominant inheritance, but the underlying mutations are at different sites on chromosome 17. The mutation responsible for hereditary brachial plexopathy is SEPT9 located in chromosome 17q25.
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