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Movement disorders (MDs) are a broad spectrum of motor and nonmotor disturbances arising from the dysfunction of subcortical motor control circuitry, including basal ganglia and thalamus, as well as other parts of the nervous system, involving the cortex, cerebellum, central, and peripheral autonomic nervous system. Patients suffering from MDs have normal muscle strength and sensation, but their normal voluntary motor activities are influenced or impaired by involuntary movement, alteration in muscle tone or posture, and loss of coordination or regulation—either facilitation or inhibition—of pyramidal motor activities as a result of malfunction. MDs can be classified into the following categories on the basis of their clinical manifestations: tremor, chorea and choreoathetosis, dystonia, myoclonus, tics, and ataxia. MDs include less movement (hypokinesia or akinesia), or excessive movement (hyperkinesias), or both (Table 44-1).
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ESSENTIALS OF DIAGNOSIS
Cardinal motor features
Bradykinesia
At least one of the following: 4–6-Hz resting tremor, muscular rigidity, postural instability (late presentation).
Absence of a secondary cause.
At least three supportive criteria: unilateral onset, progressive, resting tremor, persistent asymmetry affecting side of onset most, excellent reponse (70–100%) to levodopa, severe levodopa-induced chorea, levodopa response for ≥5 years, or clinical course of ≥10 years.
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General Considerations
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Parkinson’s disease (PD) is the second most common progressive neurodegenerative disorder after Alzheimer’s disease but remains the only neurodegenerative disease for which symptoms can be effectively controlled medically. It affects 1% of the global population aged 65 years and may double in 2030 with aging of the population. Numerous hypotheses have been explored to explain the process of the neurodegeneration, such as the effects of environment, genetics, or inflammatory processes, or defects in mitochondrial function, or oxidative stress, but without a definitive conclusion. Aging is the greatest risk factor associated with PD. Approximately 95% of PD cases are idiopathic/sporadic and occur in people aged >50 years. The incidence of PD is 1.5–2 times higher in males. Other risk factors include head trauma and exposure to pesticides or herbicides in association with rural living or exposure to well water. Five genes, including the best studied leucine-rich repeat kinase 2 (LRRK2, autosomal-dominant) and parkin (autosomal-recessive), may be the cause of 2–3% of PD. New genetic foci have been identified or investigated. An individual may have a doubled risk ...