Acute spinal cord lesions, such as infarction or compression, may produce a flaccid, areflexic paralysis that mimics lower motor neuron disease. A child who exhibits an acute or subacute flaccid paraparesis is most likely to have eitheran acute cord syndrome or Guillain-Barré syndrome. Thehallmarks of spinal cord disease are a sensory level, a motorlevel, disturbance of bowel and bladder function, and local spinal pain or tenderness. The acute cord syndrome maybe the result of transverse myelitis, cord tumor, infarction, demyelination, or trauma. Transverse myelitis, an acute postinfectious demyelinating disorder of the spinal cord, istreated with high-dose steroids. Trauma and tumors (neuroblastoma, lymphoma, sarcoma) compressing the spinalcord necessitate immediate neurosurgical management topreserve vital function.
Neuromuscular disease affects any component of the lower motor neuron unit. The distribution of muscle weakness can point toward specific diseases (Table 182-3).
Progressive degeneration of anterior horn cells is the key manifestation of spinal muscular atrophy (SMA), a genetic diseasethat may begin in intrauterine life or any time thereafter. About control, but not total loss of movement because motor nuclei of the basal ganglia, thalamus, and brainstem have tracts that produce simple or complex stereotyped patterns of movement. Thecorticospinal tract permits fine motor activity and is best testedby rapid alternating movements of the distal extremities. Milddysfunction produces slowed, stiff motions. More severe dysfunction produces stiff, abnormal involuntary postures (spasticity) consisting of forearm flexion at the elbow and wrist andadduction close to the chest, with leg extension and adduction.
Damage to the spinal cord leaves residual simple, stereotyped reflex movements coordinated by local spinal reflexes below the level of the lesion. Destruction of the lower motor
Brain tumor Trauma (accidental, nonaccidental) Infection (meningitis, encephalitis, abscess) Ischemia (arterial or venous) Hemorrhage Metabolic disease (leukodystrophy; inborn error of metabolism; mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) Degenerative disease
Botulism Myotonic dystrophy Congenital myotubular myopathy Miller Fisher variant of Guillain-Barré
Botulism Polio Miller Fisher variant of Guillain-Barré 25% of patients have a severe infantile form (SMA type1/Werdnig-Hoffmann disease), 50% have a late infantile and more slowly progressive form (SMA type 2/Kugelberg-Welander syndrome), and 25% have a more chronic,juvenile form (SMA type 3). SMA is one of the most frequentautosomal recessive diseases, with a carrier frequency of 1 in 50.
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The earlier in life the process starts, the more severe the progression. Infants with SMA type 1 present in early infancy with severe hypotonia, generalized weakness, and facial involvement. Infants have normal cognitive, social, and language skills and sensation. Fasciculations (quivering of the lateral aspect of the tongue) are best identified by inspecting the mouth when the child is asleep. Deep tendon reflexes are absent. With progression, breathing becomes rapid, shallow, and predominantly abdominal. In an extremely weak child, respiratory compromise leads to atelectasis, pulmonary infection, and death. Most infants with SMA type 1 die within the first 2 years. Children with SMA type 2 may survive to adulthood. Children with SMA type 3 can appear normal, with slower progression of weakness and a normal life expectancy.