Amyotrophic lateral sclerosis (ALS) is a progressive disorder of unknown cause, characterized primarily by loss of upper and lower motor neurons. This includes the large pyramidal motor neurons of the cerebral cortex, brainstem motor nuclei, and anterior horn cells of the spinal cord. Because there are no specific biological markers or radiographic findings that define the disease, diagnostic criteria are established based on the neurological examination and electrodiagnostic studies, supplemented by neuroimaging and laboratory studies to exclude disorders that may mimic ALS, and by neuropathological studies that may support or exclude the diagnosis. Patients with ALS demonstrate evidence of upper motor neuron (UMN) and lower motor neuron (LMN) dysfunction, with spread of symptoms or signs over time. It is possible for a patient to develop a clinical syndrome that is characterized by some or all of these features and occurs in the setting of a known malignancy, or one in which a malignancy is identified as being present concurrently with, or shortly after the appearance of, the neurological syndrome. These ALS-like syndromes may or may not meet all criteria for ALS and may be associated with other neurological symptoms and signs outside the motor system. The term motor neuron disease (MND) may be used to describe some such patients.
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