 Introduction/Background Movement disorders and neurodegenerative diseases are a variety of conditions that involve progressive neuronal degeneration, injury, or death and may involve the cortex, deep gray nuclei, subcortical white matter, brainstem, cerebellum, and spinal cord, along with connections to associated motor pathways in the cortex or extrapyramidal system. Movement disorders can present as either hypokinetic disorders, which include the Parkinsonian syndromes (idiopathic and atypical), or hyperkinetic disorders, which include Huntington disease (HD), prion disease, and neurodegeneration with brain iron accumulation (NBIA). Motor neuron diseases are a related group of syndromes that involve degeneration of upper or lower motor neurons. Amyotrophic lateral sclerosis (ALS) is the most common motor neuron disease and is characterized by degeneration of both the upper and lower motor neurons. Establishing the correct diagnosis of a movement disorder or neurodegenerative process can be difficult because of the variable and complex features of these conditions, the unusual clinical presentations of some of these patients, and the overlapping symptoms and characteristics. A combination of imaging techniques is often needed for complete evaluation of the patient and to help establish the most likely diagnosis. Initial assessment using structural imaging, with MRI preferred over CT, is helpful not only to look for patterns of atrophy, parenchymal abnormality, or abnormal substance deposition but also to exclude other potential etiologies, including underlying structural or vascular lesions, autoimmune or infectious processes, drug or medication toxicity, or hydrocephalus.
Movement Disorders and Neurodegenerative Diseases.  Introduction/Background Movement disorders and neurodegenerative diseases are a variety of conditions that involve progressive neuronal degeneration, injury, or death and may involve the cortex, deep gray nuclei, subcortical white matter, brainstem, cerebellum, and spinal cord, along with connections to associated motor pathways in the cortex or extrapyramidal system. Movement disorders can present as either hypokinetic disorders, which include the Parkinsonian syndromes (idiopathic and atypical), or hyperkinetic disorders, which include Huntington disease (HD), prion disease, and neurodegeneration with brain iron accumulation (NBIA). Motor neuron diseases are a related group of syndromes that involve degeneration of upper or lower motor neurons. Amyotrophic lateral sclerosis (ALS) is the most common motor neuron disease and is characterized by degeneration of both the upper and lower motor neurons. Establishing the correct diagnosis of a movement disorder or neurodegenerative process can be difficult because of the variable and complex features of these conditions, the unusual clinical presentations of some of these patients, and the overlapping symptoms and characteristics. A combination of imaging techniques is often needed for complete evaluation of the patient and to help establish the most likely diagnosis. Initial assessment using structural imaging, with MRI preferred over CT, is helpful not only to look for patterns of atrophy, parenchymal abnormality, or abnormal substance deposition but also to exclude other potential etiologies, including underlying structural or vascular lesions, autoimmune or infectious processes, drug or medication toxicity, or hydrocephalus.