CHAPTER 82 ■ WEAKNESS KATIE A DONNELLY, XIAN ZHAO INTRODUCTION Weakness is defined as an inability to generate normal voluntary force in a muscle or normal voluntary torque about a joint Although often associated, hypotonia is not synonymous with weakness Neurologists define hypotonia as decreased resistance to passive motion Not all hypotonic patients are weak; for example, a patient with Down syndrome may have normal strength yet have decreased tone PATHOPHYSIOLOGY Weakness is a reflection of a disease process that may involve any component of the motor neuron unit These diseases are classically categorized as upper or lower motor unit disorders ( Table 82.1 ) Upper motor neuron disease affects structures extending from the motor strip of the cerebral cortex, through the corticospinal tracts of the spinal cord, to (but not including) the anterior horn cell Although upper motor neuron disease is generally characterized by increased deep tendon reflexes (DTRs) and spasticity, early in the clinical course there may be flaccid paralysis Lower motor neuron disease may involve the anterior horn cell, the peripheral nerves, the neuromuscular junction (NMJ), or the muscle fibers In general, lower motor neuron disease is associated with fasciculations, muscle atrophy, hypotonia, and hyporeflexia, and may ultimately lead to flaccid paralysis DIFFERENTIAL DIAGNOSIS The cerebral cortex can be damaged by cerebrovascular accidents (CVAs), which include cerebral infarctions and cerebral hemorrhages CVAs, while rare (2.1 to 13.1 per 100,000 children per year), cause some of the most catastrophic cases of weakness ( Table 82.2 ) These children usually present with sudden onset of unilateral or asymmetric weakness Cerebral hemorrhage is usually due to a ruptured arteriovenous malformation (AVM), but may also be caused by a ruptured aneurysm Most AVMs are asymptomatic until rupture, but some children complain of periodic “migraine-like” headaches Brain tumor hemorrhage may also present acutely as weakness, severe headache, and vomiting Cerebral infarctions usually occur in the setting of predisposing factors, which include sickle cell disease, homocystinuria, structural arterial disease (e.g., moyamoya), and hypercoagulable states (e.g., antithrombin III, protein C and S deficiencies, and factor V Leiden mutations) Other more common hypercoagulable states include pregnancy, malignancy, infections, and severe dehydration Recent studies have shown increased risk associated with hypertension, diabetes, obesity, and hypercholesterolemia in younger teenage populations Substance abuse with tobacco, alcohol, cocaine, and amphetamines are also associated with cerebral infarction Atherosclerosis and atrial fibrillation, common culprits in adult stroke, remain rare causes of stroke in children Embolic causes that should be considered in pediatric patients include children with congenital heart disease, mitral valve prolapse, or a history of rheumatic fever Transient ischemic attacks (TIAs) often present with resolving weakness TIAs are defined as transient neurologic deficits referable to a cerebral artery territory in a child whose cranial magnetic resonance imaging (MRI) shows no acute ischemia, but whose history/workup suggests cerebrovascular disease Transient focal deficits are common after a seizure and are called Todd paralysis Deficits usually resolve within minutes to hours after a seizure, but one study demonstrated a mean symptom duration of 15 hours and persistence of up to 36 hours In this same study, 8/14 patients with Todd paralysis had an underlying CNS lesion Because a Todd paralysis resolves with time, if the patient is regaining function in 30 to 45 minutes, the differential diagnosis should be broadened to ensure a cerebrovascular event or mass lesion is not the cause of the focal weakness Cranial imaging is crucial in cases of prolonged postictal paralysis, especially if the mental status remains impaired, or if other focal deficits persist The reference standard study is MRI However, access to MRI may be limited or may not be immediately practical (e.g., need for deep sedation) Consequently, a computed tomography (CT) scan of the head is often the initial study of choice The head CT is most useful to rule out acute bleeds and large mass lesions In some cases, a CT angiogram is necessary to identify vascular lesions or anomalies Traumatic injuries may seriously damage or compress the spinal cord Spinal cord concussion is defined as a transitory disturbance in spinal cord function caused by a direct blow to the back Symptoms may include flaccid paraplegia or quadriplegia, a sensory level at the site of injury, loss of tendon reflexes, and urinary retention Recovery usually begins within a few hours and is usually complete within a week Spinal epidural hematoma may cause spinal cord compression as the hematoma expands Emergent spinal MRI scanning is indicated when an epidural hematoma is suspected Other traumatic injuries include vertebral body compression fractures, dislocations, and spinal cord transections Another serious cause of spinal cord compression is epidural abscess, which is usually caused by hematogenous spread of bacteria, most commonly Staphylococcus aureus, or by direct spread from an adjacent carbuncle or vertebral osteomyelitis This is a rare (0.2 to 1.2 per 10,000 hospital admissions), but potentially devastating disease entity often unidentified until progression to severe neurologic sequelae Patients commonly present with fever and back pain, but may also have headache, vomiting, stiff neck, and bowel and bladder dysfunction In young children with epidural abscess, the constellation of symptoms may suggest meningitis or a septic hip Point tenderness may be elicited over the affected area The diagnosis is confirmed by MRI, which helps also to distinguish the abscess from a vertebral discitis Similarly, spinal cord tumors are another important cause of spinal cord compression TABLE 82.1 DIFFERENTIAL DIAGNOSIS OF WEAKNESS ... adult stroke, remain rare causes of stroke in children Embolic causes that should be considered in pediatric patients include children with congenital heart disease, mitral valve prolapse, or a history