After studying this chapter, the student should be able to:
Understand the various pathologies underlying movement disorders.
Identify and distinguish the clinical features of the various movement disorders and correlate these with basal ganglia anatomy.
Identify the various medical and surgical treatments for movement disorders.
Given the breadth of pathologies responsible for the various movement disorders, there is great variation in disease prevalence. More will be discussed later for each of the diseases, but in general, movement disorders are relatively common neurologic problems. The most prevalent movement disorder is essential tremor, with a prevalence of roughly 400 per 100,000. While essential tremor is common, many of the cases are mild, and often these patients do not seek treatment. The most common movement disorder encountered in clinical practice is Parkinson disease, a serious and debilitating disorder affecting approximately 200 people per 100,000 population and >1 million people in the United State and 10 million people worldwide. Combined direct and indirect cost of care of US patients with Parkinson disease is estimated at $25 billion per year. Huntington disease is rare, with a prevalence in the 7 per 100,000 range.
The entire motor system is quite extensive, spanning from motor cortex to muscle. For simplicity, however, disorders of the motor system are divided anatomically. Disorders involving the corticospinal tract (pyramidal) extending out to the peripheral muscle are classified as neuromuscular disorders (see Chapter 31). Disorders of the basal ganglia and cerebellum (extrapyramidal) are grouped into the field of movement disorders and will be discussed here. Pathways through the basal ganglia moderate and adjust voluntary movement (Figure 28–1). The direct pathway primarily facilitates movement (“go”), whereas the indirect pathway primarily inhibits movement (“no go”).
Functional circuitry between the cerebral cortex, basal ganglia, and thalamus. The major neurotransmitters and their excitatory (+) or inhibitory (−) effects are indicated. In Parkinson disease, there is degeneration of the pars compacta of the substantia nigra, leading to overactivity in the indirect pathway (red) and increased glutamatergic output from the subthalamic nucleus. GABA, γ-aminobutyric acid. (Reproduced with permission from Katzung BG: Basic and Clinical Pharmacology, 14th ed. New York, NY: McGraw Hill; 2018.)
We will discuss each of the main movement disorders, but to establish a framework, most movement disorders are classified as either predominately hypokinetic (too little movement) or hyperkinetic (too much movement). The prototypical hypokinetic movement disorder is Parkinson disease, whereas the prototypical hyperkinetic movement disorder is Huntington disease.
HYPOKINETIC MOVEMENT DISORDERS
Parkinsonism is the umbrella term for a tetrad of symptoms: rigidity, resting tremor, bradykinesia, and postural instability. Together, these are the cardinal signs of parkinsonism. Rigidity...