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ESSENTIALS OF DIAGNOSIS
Muscle weakness and atrophy
Absence of overt cognitive and sensory changes
Altered tendon reflexes—hyperactive if upper motor neurons (UMNs) are affected and either hypoactive or absent if lower motor neurons (LMNs) are involved
Babinski sign (if UMN is involved)
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General Considerations
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By convention, the term motor neuron disease encompasses disorders that predominantly or exclusively affect upper motor neurons, lower motor neurons, or both. By definition, sensory neurons are spared in these diseases. Motor neuron diseases can be acquired or inherited; however, the most common of these diseases in adults, amyotrophic lateral sclerosis (ALS), is typically sporadic and its cause is unknown (Tables 20–1 and 20–2).
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