Chapter 54: Weakness

• Upper motor neuron diseases usually present with asymmetrical weakness contralateral to the lesion. Lower motor neuron diseases present with symmetrical weakness that can be isolated to specific muscle groups.

• Involvement of bulbar muscles is manifested by cranial nerve findings, facial muscle weakness, and chewing or swallowing difficulties. Bulbar involvement can occur in both upper and lower motor neuron disorders.

• Neuropathies are disorders of nerves and tend to cause distal muscle weakness, hypesthesias or paresthesias, and decreased reflexes, especially early in the disease.

• Myopathies are disorders of muscle and can be inflammatory or congenital. Inflammatory myopathies usually involve proximal muscles and are associated with muscle pain or tenderness.

• Guillain–Barré syndrome (GBS) often starts with paresthesias in the fingers and toes, and nonspecific muscular pain, most often in the thighs. The pain is followed by ascending weakness, which results in trouble walking or balance problems.

• Infantile botulism is caused by colonization of the intestinal tract by spores of Clostridium botulinum. Many cases are linked to nearby construction projects, as soil harbors the spores. A prominent early manifestation is constipation.

The term “weakness” can refer to a general phenomenon that affects all or most of the body or may refer to a specific area, such as an extremity. The complaint can imply generalized fatigue, refusal to walk, increased clumsiness, loss of bowel or bladder function, or focal motor weakness. In infants, weakness can imply lethargy, poor feeding, or poor head control. Slowly progressive forms of weakness may be due to congenital disorders. The child may present at a time when the weakness is mild, yet progressive. Others may have paralysis at the time of presentation. The primary focus in this chapter is on weakness arising from neuromuscular disorders.

The pathophysiology of weakness varies with the etiology and the specific area affected. Terms that are applied to neuromuscular disorders include the following:

• Paresis implies a complete or partial weakness.

• Paraparesis is weakness of the lower half of the body.

• Quadraparesis is weakness involving all limbs.

• Hemiparesis is weakness of one side.¹

• Quadriplegia is paralysis of all limbs; it usually results from a spinal cord lesion.

• Hemiplegia, involving one side of the body, generally results from a lesion in the brain.

Abnormalities of the neuromuscular system are further classified as arising from an upper or lower motor neuron unit. The upper motor neuron unit arises in the motor strip of cerebral cortex, traverses the corticospinal tract, and ends in the spinal cord adjacent to the anterior horn cell.^2,3 Upper motor neuron diseases involving the cerebral cortex or spinal cord usually present with asymmetrical weakness that is contralateral to the lesion, and are associated with hyperreflexia, increased muscle tone, and the absence of atrophy or fasciculations.^3–5 The lower motor neuron unit includes the anterior horn cells, peripheral nerve, neuromuscular junction, and muscle fibers. Lower motor neuron diseases present with symmetrical weakness that can be isolated to specific muscle groups, and are associated with decreased muscle tone and depressed reflexes. Depending on whether the disorder is acute or chronic, atrophy and fasciculations may be present (Table 54-1).^2,3,5,6

Involvement of bulbar muscles is manifested by cranial nerve findings, facial muscle weakness, and chewing or swallowing difficulties. Bulbar involvement can occur in both upper and lower motor neuron disorders.¹

In the patient presenting with weakness, it is important to distinguish between neuropathy and myopathy. Neuropathies are disorders of nerves, and tend to produce distal muscle weakness, hypesthesias or paresthesias, and decreased reflexes, especially early in the disease. The progression of weakness and sensory loss is in a stocking and glove distribution.^6,7 Myopathies are disorders of muscle, and can be inflammatory, infectious, congenital, or metabolic. Inflammatory myopathies usually involve proximal muscles and are often associated with muscle pain or tenderness. Reflexes become decreased late in the disease. Congenital myopathies tend to involve specific muscle groups, and can present at birth with hypotonia and weakness, or in older children with a more insidious progression.^3,8

History

It is vital to distinguish between acute and chronic disorders, since this information will direct the remainder of the workup. The location of the initial weakness is elicited, and weakness is established as focal or general. Focal weakness is further characterized as predominantly proximal or distal. The rate of progression of symptoms is characterized as acute, which implies minutes to hours; subacute, meaning hours to days; and slowly progressive, which involves a prolonged period. Acute onset or rapid progression implies spinal cord compression or a vascular event involving the spinal cord or brain. Subacute progression can be due to infection, inflammation, toxin, or tumor. Slowly progressive symptoms imply a chronic or congenital disorder.³ Defining the progression of symptoms is facilitated by asking the parents questions regarding progressive difficulty in walking, recent difficulty climbing up or down stairs, or inability to go from a sitting to standing position unaided. The loss of developmental milestones implies a degenerative disorder.⁷

The patient and parents are questioned regarding symptoms preceding the onset of weakness, such as recent illness, fever, headache, neck or back pain, loss of bowel or bladder function, or trauma. Prior episodes of weakness may suggest an intermittent metabolic problem. A family history of weakness suggests a congenital disorder. A history of exposure to drugs or heavy metals suggests poisoning. A pertinent travel history is indicated, as weakness can be a manifestation of entities such as tick paralysis, or from ciguatera poisoning. A careful antenatal history is indicated to rule out a perinatal insult, as is an immunization history to evaluate the possibility of a vaccine-related complication.

Physical Examination

The physical examination begins with observation of mental status, posture, gait, and the ability of the child to get on the examining table or to sit unaided. The vital signs are assessed, with particular attention to respiratory rate and effort, as many neuromuscular disorders are associated with a risk of respiratory failure. Blood pressure and pulse are carefully monitored, as some neuromuscular disorders, such as Guillain–Barré syndrome (GBS), are associated with autonomic instability.

The patient's general appearance is noted, with attention given to general muscular development and the presence of kyphosis, scoliosis, or lordosis, which can all suggest a congenital disorder. Lack of facial expression, snarl, or slack jaw suggests myasthenia gravis. Ptosis can be due to myasthenia or myotonic dystrophy. Inspect the muscles for wasting, fasciculation, or hypertrophy.

The neurologic examination includes an evaluation of pupillary size and reactivity and the remainder of the cranial nerves. If possible, the fundus is examined and the visual fields are assessed. One way to test facial strength is to have children blow out their cheeks and resist compression.⁸ For patients old enough to cooperate, motor strength in the extremities is evaluated and rated on a scale of 0 to 5 (Table 54-2).^1,5,7 For infants who cannot cooperate with the examination, it is possible to perform a general assessment of muscle tone and integrity by holding the baby under the arms and placing the feet on the bed. Infants with normal tone will not slide through an examiner's hands and will actively kick both legs against the resistance of the bed. In an outstretched prone position, infants supported on the trunk should hold their head up, flex the limbs, and keep their back straight.² Older children can be asked to walk on their toes and heels. The ability to walk on the heels but not the toes suggests intraspinal pathology, although toe walking can occur with upper motor neuron disorders that cause spasticity.⁸

Deep tendon reflexes at the knees, ankles, elbows, and wrists are elicited.¹ Hyperreflexia or sustained clonus indicates an upper motor neuron lesion, whereas absent or decreased reflexes imply a problem in a lower motor distribution.² Other reflexes to be noted include the anal wink, the plantar response, and abdominal and cremasteric responses.

Sensory evaluation includes touch, pain, position, vibration, and temperature. Touch and pain are evaluated by assessing soft versus sharp stimulation and two-point discrimination. Position sense is assessed by asking the child to indicate the direction in which an examiner moves a finger or toe. Temperature sensation can be assessed by the use of a cold stethoscope or by touching the child with cold or warm water. Vibration can be tested using a tuning fork on both thumbs (interphalangeal joint) and big toes.^1,7

The sensations of touch and position-vibration do not cross in the spinal cord on their way to the brain, whereas those of pain and temperature do. An abnormality of touch and position on one side and pain and temperature on the other suggests a cord lesion. The unilateral loss of all sensations suggests a brain lesion. A stocking and glove distribution of sensory loss suggests a peripheral neuropathy.

Laboratory Evaluation

The laboratory evaluation is based on the provisional diagnosis. Generally, complete blood counts, serum electrolytes, calcium, magnesium, and phosphorus are indicated.^4,7 Elevated serum creatine kinase is nonspecific but is found in children with active inflammatory myopathies and is extremely elevated in congenital myopathies.⁹ Urine is assessed for the presence of myoglobin and, in selected cases, is used for toxicology screening.^4,7

For patients with a suspected spinal cord lesion, radiographs are indicated. Even if they are negative, any patient suspected of having a developing lesion of the spinal cord requires evaluation by magnetic resonance imaging (MRI). If this is unavailable, computed tomography (CT) of the spine may be helpful.

For patients with suspected central nervous system lesions, an imaging study of the brain is indicated. Some patients may require a lumbar puncture.³

Electromyography and nerve conduction studies are indicated if lower motor neuron disease is suspected, and to distinguish neuropathic from myopathic etiologies.^2,4,8,10 Muscle biopsies are also of value to diagnose specific neuromuscular diseases.^2,4

Weakness due to certain causes is common enough in the pediatric ED population to justify specific discussion.

Guillain–Barré Syndrome

GBS is now considered a heterogeneous syndrome.¹¹ The most common form of GBS is acute inflammatory demyelinating polyradiculoneuropathy (AIDP).^3,11 GBS is the most common cause of acute motor paralysis in children.^3,11 The pathogenesis is thought to result from an immune response to an antecedent infection that triggers demyelination of nerve roots and peripheral nerves. Campylobacter infection is the most common preceding illness, occurring in 30% of cases. Other infections include cytomegalovirus, EBV, herpes simplex, Haemophilus influenzae, Mycoplasma pneumoniae, hepatitis A and B, enterovirus, and Chlamydophila pneumoniae.^11,12 The form of GBS associated with campylobacter also results in acute axonal degeneration.¹¹ The syndrome often starts with paresthesias in the toes and fingers, and nonspecific muscular pain, most often in the thighs. The pain is followed by weakness, which is most often symmetric and distal, then results in trouble walking or balance problems.^11,12 Weakness progresses upward and, in some cases, results in total paralysis within 24 hours. Cranial nerve involvement is common, with bilateral facial weakness. Deep tendon reflexes are usually absent, but plantar responses remain downgoing. Autonomic involvement can produce labile changes in blood pressure and bowel and bladder incontinence. The degree of weakness and the rate of progression of disease vary considerably. Laboratory findings are generally not helpful, although spinal fluid analysis may reveal a high protein (>45 mg/dL) and usually has fewer than 10 white blood cells.^11,12

Electrophysiologic studies demonstrate motor conduction block, and slowed nerve conduction velocities.^11,12

The basic treatment for GBS is supportive care. Patients with vital capacity half normal for age or ≤20 mL/kg body weight usually require ventilatory support. Approximately 20% of patients require mechanical ventilation, which is associated with a poorer prognosis.¹³ Attention is given to fluid and electrolyte balance, heart rate, cardiac rhythm, blood pressure, and nutritional needs. Intravenous immunoglobulin (IVIG) has been shown to shorten the course, as have limited studies on plasmapheresis.¹³

There are other variants of GBS in children, which includes Miller–Fisher syndrome, which is characterized by ophthalmoplegia, hyporeflexia, and ataxia.^11,12 Acute motor axonal neuropathy (AMAN) occurs mainly in China, and is associated with a preceding campylobacter infection.^11,12It involves mainly motor neurons, and results in axonal damage. Acute motor and sensory axonal neuropathy (ASMAN) has more sensory symptoms, a more prolonged course, and limited recovery.^11,12

Acute Central Nervous System Demyelination

Acute disseminated encephalomyelitis (ADEM) usually occurs following a viral or bacterial illness, but can occur postvaccination. It is characterized by fever, encephalopathy (confusion, irritability, lethargy), headache, and neurologic findings such as cerebellar ataxia, acute hemiparesis, spinal cord dysfunction, or cranial neuropathies.^14–16 Diagnosis is based on MRI showing bilateral, multifocal, large hyperintense lesions in the white matter, but can also occur in the gray matter as well as in the spine.^14–16 Cerebrospinal fluid (CSF) may show elevations in white blood cell count (>50) and protein.^15,16 Patients should be started on high-dose IV corticosteroids, along with IV antibiotics and acyclovir until CSF cultures are known. High-dose steroids are continued for 3–5 days followed by a taper over 4 to 6 weeks.¹⁷ For those unresponsive to steroids, IVIG or plasma exchange can be tried.¹⁷ ADEM can be recurrent or multiphasic (occurring more than 3 months later with new symptoms or MRI findings and occurring at least 1 month following steroid taper).^14–16

Pediatric multiple sclerosis (MS) is characterized by recurrent episodes of demyelination separated by at least 4 weeks, and more frequently occurs in those older than 10 years of age. MRI can be used for the diagnosis when it shows three of the following: nine or more white matter lesions or one gadolinium enhancing lesion; three or more periventricular lesions; one juxtacortical lesion; or an infratentorial lesion.¹⁵

Clinically isolated syndrome (CIS) is the first demyelinating illness, in which there is no encephalopathy or fever. This includes optic neuritis, transverse myelitis, and dysfunction of the brainstem, cerebellum, or hemispheres.^14,15

Transverse myelitis is a syndrome characterized by acute dysfunction at a level of the spinal cord. Patients may initially complain of paresthesias and weakness of the lower extremities. Those with the rapid form often complain of back pain. Progressive weakness, paraplegia, and urinary retention usually result, and a sensory level may develop, most commonly in the thoracic area. Flaccid paralysis and decreased reflexes are characteristic early in the process but are later followed by increased muscle tone.^5,14 For a patient with signs of a rapidly advancing spinal cord lesion, it is imperative to exclude a treatable mass lesion that could be compressing the cord, such as an epidural abscess or hemorrhage. This is usually done by MRI, which shows a gadolinium signal abnormality over the spinal cord, and may show swelling on weighted T2 images.¹⁴ Most patients with transverse myelitis recover some function.

Neuromyelitis optica (Devic disease) is the combination of bilateral optic neuritis and transverse myelitis. Diagnosis is based on the presence of an NMO-IgG autoantibody or the presence of a spinal lesion extending over three or more segments on MRI.^14,15

Tick Paralysis

Tick paralysis is caused by a neurotoxin from the Rocky Mountain wood tick (Dermacentor andersoni) or the Eastern dog tick (Dermacentor variabilis). The tick produces a neurotoxin that prevents liberation of acetylcholine at neuromuscular junctions. Several days after the female tick attaches, the patient begins to experience paresthesias, fatigue, and weakness, which progresses to ataxia and difficulty walking.¹⁸ Paralysis is ascending, and the sensory exam is intact. Deep tendon reflexes are absent. In some cases, there can be facial and bulbar muscle involvement, or unilateral paralysis. If the tick is not removed, flaccid paralysis and death can result. Removal of the tick is generally curative within a few hours.^8,18

Botulism

Infection with Clostridium botulinum can produce three neurologic diseases. Ultimately, symptoms result from a toxin generated from spores of the bacteria that inhibits calcium-dependent release of acetylcholine at the prejunction of terminal nerve fibers.¹⁹

Food-borne botulism results from ingestion of food containing the toxin. Diarrhea and vomiting are followed by neurologic symptoms, often secondary to cranial nerve dysfunction. Blurred vision, dysarthria, and diplopia can occur and can be followed by weakness of the extremities. Mucous membranes of the mouth and pharynx may be dry. Deep tendon reflexes may be weak or absent.¹⁹ Wound botulism results from infection of a contaminated wound, 4 to 14 days after the wound is infected. Clinically, it is usually indistinguishable from food-borne botulism. Treatment includes wound debridement and antibiotic therapy.¹⁹

Infantile botulism is caused by colonization of the intestinal tract by spores of C. botulinum, which releases toxin that is systemically absorbed. It has been related to the ingestion of contaminated honey, but most cases are linked to nearby construction projects, as soil harbors the spores. The affected age group is 1 week to 12 months. A prominent manifestation is constipation. The infant develops a descending paralysis, with ptosis, difficulty in sucking and swallowing, reduced facial expression, followed by hypotonia. Automonic signs include decreased tearing and salivation, flushed skin, and variable blood pressure and heart rate.^19,20 Progression to respiratory failure, with the need for mechanical ventilation can occur.²⁰

Diagnosis is by isolating the toxin in the infant's stool, but because this takes several days, if the diagnosis is suspected, treatment with IV botulism immune globulin (baby BIG) should be given.²⁰ Electromyography is also useful, but findings are not pathognomonic.²⁰

Myasthenia Gravis

The term myasthenia gravis comprises a group of autoimmune diseases characterized by easy fatigability. It is associated with anti-acetylcholine receptor antibodies resulting in decreased transmission of nerve impulses across the neuromuscular junction. It is the most common disorder of the myoneural junction in children.¹⁹ In children, the striated muscles innervated by the cranial nerves are particularly affected. The diagnosis is usually established by demonstrating improvement in muscle strength after administration of the anticholinesterase drug. Neonatal transient myasthenia gravis occurs in infants born to mothers with the disease, and is caused by maternal anti-acetylcholine receptor antibodies that cross the placenta. It affects 10% to 20% of infants whose mothers have myasthenia gravis. The infant may have a weak cry or suck, ptosis, generalized weakness, hypotonia, and respiratory distress. It presents in the first few hours of life, but may be delayed up to 3 days. Treatment is with neostigmine or pyridostigmine. The disease usually improves in 4 to 6 weeks, but may last for months.^19,20 Juvenile myasthenia gravis is similar to that seen in adults. It commonly has its onset at around 10 years of age, and is more common in females. Ptosis, ophthalmoplegia, and weakness of other facial muscles are commonly present. This results in difficulty in chewing, dysarthria, and dysphagia. Bulbar weakness develops in 75% of patients.¹⁹ Symmetrical limb weakness is usually present, and affects the proximal muscles more than the distal muscles. The disease tends to become worse throughout the day, but can also worsen with stress or exertion. Symptoms and signs can be scored on a validated myasthenia scoring system and activities of daily living scale. Both remissions and exacerbations are common. Electrophysiologic testing and the presence of serum anti-acetylcholine receptor antibodies result in a more specific diagnosis.¹⁹ The primary treatment is with anticholinesterase agents. In refractory or severe cases, immunosuppressive agents, corticosteroids, IVIG, plasmapheresis, or thymectomy may be necessary. Erythromycin, tetracycline, aminoglycoside antibiotics, anesthetic drugs, neuromuscular blockers, and muscle relaxants therapy can exacerbate symptoms and should be avoided.^19,21 Myasthenic crisis results in profound weakness, difficulty in swallowing secretions, and respiratory insufficiency. It is often precipitated by infection, surgery, or decreasing immunosuppressive drugs. It can also be exacerbated by the use of antibiotic therapy, especially aminoglycosides as well as antiarrhythmics, ophthalmologic medications, and magnesium.²¹ If a myasthenic crisis is suspected, the patient is admitted to an intensive care unit where respiratory status can be monitored, and elective intubation can occur if needed. Patients with myasthenia gravis can also suffer from overdose of anticholinesterase medications, which can provoke a cholinergic crisis. Unfortunately, the symptoms of cholinergic excess are similar to those of a myasthenic crisis. In both, increasing weakness is the predominant finding.²² Patients suffering a cholinergic crisis may also have associated vomiting, diarrhea, and hypersalivation. In patients with obvious severe cholinergic excess, atropine or glycopyrrolate may be useful in drying airway secretions.²² However, in most cases, it will be difficult to distinguish between a cholinergic crisis and an exacerbation of myasthenia, and hospital admission and close observation are indicated.

Bell's Palsy

Bell's palsy is a condition that results in unilateral facial weakness. In severe cases, there can be total paralysis of the facial muscles. It is thought to result from swelling and edema of cranial nerve VII, the facial nerve, as it traverses the facial canal within the temporal bone. As such, it is a peripheral neuropathy, and the distribution of the weakness reflects the territory innervated by the facial nerve. The nerve has motor, sensory, and autonomic functions and, in addition to supplying the muscles of the face, it innervates the lacrimal and salivary glands, and the anterior two-thirds of the tongue. In most cases, Bell's palsy is idiopathic. Certain conditions are associated with unilateral facial weakness, including herpes zoster or simplex infections, otitis media, Lyme disease, and temporal bone trauma.²³ Symptoms may begin with ear pain, which is followed by the development of facial weakness, characterized by a drooping mouth, and inability to close the eye on the affected side. In some cases, lacrimation and taste are impaired. Inability to close the mouth can make eating and drinking difficult.²³ The lesion is identified as a peripheral neuropathy, as opposed to a lesion of the central nervous system, by the fact that Bell's palsy affects the muscles of the forehead on the side of the lesion. In a lesion of the central nervous system, the forehead is spared, because it receives innervation from both sides of the brain. A lesion in a cerebral hemisphere will cause weakness confined to the lower part of the face.²³ Laboratory studies are not necessary in uncomplicated cases. If the child has been in a Lyme disease endemic region, testing may be useful. If mastoiditis is suspected, a CT scan is helpful.²³ The prognosis of Bell's palsy is generally good, with recovery usually beginning in 2 to 4 weeks, but may take 6 to 14 weeks to resolve fully. Steroid therapy may be beneficial if started early in the course of illness, and is given for 1 week. Treatment includes lubricating solutions for the eye on the affected side to maintain moisture of the cornea.²³ Patients with inability to close the eye may require patching. In young children, ophthalmologic consultation may be advisable.

Peripheral Neuropathies

Peripheral neuropathies in children can be hereditary or acquired. The symptoms include a bilateral sensory loss or a feeling of burning, which is usually symmetrical and distal.²⁴ Weakness is the most common motor symptom.²⁴ If the presentation is acute, toxins such as heavy metals (arsenic, lead, mercury, thallium), fish poisoning (ciguatera and paralytic shellfish), or organophosphates, should be considered.^5,24

Myopathies

Myopathies are diseases that affect skeletal muscle. They are relatively uncommon in children, and, in most cases, a child affected with a myopathy will present to the ED with a known diagnosis. Many myopathies are congenital.

Muscular Dystrophies

Muscular dystrophies are disorders associated with progressive degeneration of muscle. The many different varieties of muscular dystrophy vary in their mode of inheritance, age of onset, muscles involved, progression of disease, and ultimate outcome. The most common is Duchenne muscular dystrophy, usually an X-linked recessive disorder resulting in the absence of the protein dystrophin.⁹ Clinical manifestations usually become apparent before age 4, when patients begin to develop weakness of the hip girdle and shoulder muscles. Patients may have difficulty standing and characteristically rise from all fours by placing their hands on the thighs and pushing up (Gower's sign).^3,9 There is hypertrophy of the calf muscles. The disease is characterized by a progressive loss of muscle strength. Lordosis and kyphoscoliosis develop as the disease progresses. Pulmonary involvement due to weakness of the diaphragmatic and intercostal muscles results in impaired lung function. Although the use of mechanical ventilators has increased survival, pulmonary infections and respiratory insufficiency are the main causes of mortality.⁹ Cardiac insufficiency and cardiomyopathy of varying degrees occur in the majority of children. In adolescence, cardiac fibrosis can lead to left ventricular dysfunction, arrhythmias, heart failure, and sudden death.⁹ The use of daily prednisone is the only treatment. It has been shown to improve ambulation, reduce contractures, and preserve respiratory function.⁹

Periodic Paralysis

Periodic paralysis is an example of metabolic myopathies that result in muscle weakness. The disorders are usually inherited, but can also be acquired. The inherited forms are autosomal dominant. There are several varieties, which include the channelopathies affecting the potassium, sodium, and calcium channels in skeletal muscle.²⁵

Hypokalemic periodic paralysis is actually one of five channelopathies that is due most commonly to a disorder in the skeletal muscle calcium-channel gene, or is associated with thyroid disease, or cardiac dysrhythmias (Anderson syndrome).²⁵ Most episodes of hypokalemic periodic paralysis have their onset during the first or second decade of life. They are often precipitated by excitement, cold, rest after exercise, or ingestion of high-carbohydrate meals, but can also be associated with hyperthyroidism, excessive insulin, renal tubular acidosis, or laxative abuse. Paralysis usually begins proximally and spreads distally. The patient may be areflexic. The episode can last for 6 to 12 hours.^8,25 Attacks tend to decrease with age. Serum potassium during an attack is usually decreased compared with a baseline value. Treatment with oral potassium during an attack may be helpful; intravenous potassium may be needed for severe attacks. Long-term therapy with a low-sodium and low-carbohydrate diet, avoidance of exposure to cold, and potassium supplement can be beneficial. Acetazolamide taken daily may reduce the number of attacks.²⁵

The three forms of hyperkalemic periodic paralysis are also autosomal dominant conditions associated with intermittent attacks beginning in the first decade of life. Attacks can be provoked by cold exposure, periods of rest following heavy exertion, and oral potassium loads. Weakness can develop rapidly, and lasts a shorter period of time than that of hypokalemic periodic paralysis.^8,25 Myalgia develops at the outset, and is followed by proximal then distal muscle weakness. Some patients develop myotonia during attacks.²⁵ The serum potassium is elevated above baseline values, although the degree of hyperkalemia varies. Treatment with oral glucose may speed recovery. Most attacks respond to treatment with glucose and insulin. In severe cases, intravenous calcium gluconate is necessary. In such cases, nebulized albuterol is also helpful.²⁵ Preventive treatment includes avoidance of exposure to cold and avoidance of fasting. Eating frequent high-carbohydrate meals may be helpful, as is treatment with hydrochlorothiazide or acetazolamide.²⁵

Inflammatory Myopathies

Viral Myositis

Viral myositis is a common cause of weakness in children. It may follow influenza or other viral illnesses. Fever and other constitutional symptoms are accompanied by myalgias. Affected muscles are tender to touch, and may be boggy. The creatine kinase is often elevated. The urine should be examined for myoglobinuria, as this may indicate rhabdomyolysis, a serious complication. Most cases are self-limited, and are treated with bed rest, hydration, and NSAIDs or acetaminophen.^3,5,26,27

Trichinosis

This is caused by ingestion of inadequately cooked meat (usually pork) containing the parasitic nematode Trichinella spiralis. Although most infections are asymptomatic, invasion of the muscles results in an acute systemic infection characterized by fever, headache, generalized myalgias, abdominal pain, and weakness 2 to 12 days after ingestion of the meat. Myalgias and weakness are more profound in the third week of infection. Other complications include myocarditis and CNS infection. Diagnosis is by serum antibody levels, which peak 3 to 4 weeks after infection. Many patients also have elevated creatine kinase and eosinophilic leukocytosis. Treatment includes thiabendazole and prednisone to prevent a Herxheimer-like reaction after degeneration of the larvae.²⁶

Pyomyositis

This is an abscess or multifocal abscesses within the muscle. Although it is more likely to occur in an immunocompromised host, it has been occurring more frequently with the emergence of methicillin-resistant Staphylococcus aureus (MRSA). Other bacterial causes include streptococci, Escherichia coli, Yersinia, and Legionella.^3,26 The child presents with fever, muscle pain, and tenderness. The abscess can be seen on ultrasound, CT scan, or MRI. Treatment involves appropriate intravenous antibiotics and drainage of the abscess.^3,26

Poliomyelitis

Although polio is rare, there are still sporadic cases. The virus attacks the anterior horn cells, resulting in asymmetrical weakness, with proximal muscles affected more than distal ones, and absent or reduced reflexes. The child may develop nuchal rigidity, muscle tightness, and fever. In infants younger than 1 year, spasm of the back muscles is also prominent. Bulbar involvement results in respiratory compromise, circulatory and autonomic instability, and mandates ventilatory support. The CSF has pleocytosis with mononuclear cells, and a normal or slightly elevated protein.^5,6

West Nile Virus

This RNA virus has rapidly become endemic in the United States due to its vector of the Culex mosquito. Although most infections are asymptomatic, those that are symptomatic are more severe in the elderly; there have been cases in children as well. Symptoms include fever, headache, nausea, vomiting, and meningoencephalitis. Weakness may develop, and may be asymmetric or involve the face. Diagnosis is by demonstrating a rising IgM titer, or by reverse transcriptase PCR.⁶

The disposition of a patient with weakness depends on the degree of disability and the nature of the underlying problem. In any patient in whom the development of respiratory compromise is a possibility, hospital admission and close observation are recommended.