Review Question - QID 217654

This man with chronic mask-like facies (difficult to distinguish facial expressions), shuffling gait, resting tremor, and rigidity with a finding of alpha-synuclein depositions has the classic symptoms of Parkinson disease, which is diagnosed by physical examination.

Parkinson disease is a progressive nervous system disorder that primarily manifests with motor symptoms. The etiology is still considered to be idiopathic, but likely involves an interaction between host susceptibility and environmental factors. The symptoms associated with Parkinson disease are caused by the loss of a number of neurotransmitters, most notably dopamine. This occurs due to alpha-synuclein depositions in the dopamine neurons of the substantia nigra (specifically the pars compacta), which collectively form Lewy bodies and result in an overall excitatory drive in the basal ganglia. This results in decreased dopamine, which produces the resultant characteristic symptoms, such as pill-rolling tremor at rest, rigidity, shuffling gait, impaired balance, and lack of arm movement with walking. While a dopamine uptake scan can be used for diagnosis, this is not necessary in classic cases and is an expensive newer technology. The gold standard for diagnosis remains a thorough physical examination. Treatment options include levodopa-carbidopa, dopamine agonists, and monoamine oxidase-B inhibitors. Some patients may benefit from deep brain stimulation.

Zafar et al. described the pathophysiology of Parkinson disease, review the clinical features, and outline management considerations.

Figure/Illustration A depicts Lewy bodies (red arrows), which are alpha-synuclein inclusions in neurons that are a common finding in the substantia nigra of patients with Parkinson disease.

Incorrect Answers:
Answer 1: Cognitive function testing is the most appropriate diagnostic measure in patients with concern for Alzheimer disease. This condition is defined by memory impairments (short-term and long-term). This patient's physical examination findings are not diagnostic or characteristic of this pathology. Futhermore, alpha-synuclein depositions are not characteristic of this condition.

Answer 2: A dopamine uptake scan can be used, though this is an expensive newer technology that is not necessary for diagnosis. Currently, the gold-standard methodology for the diagnosis of Parkinson disease is still a physical examination, given the myriad of physical symptoms and signs that define this disorder.

Answer 3: Electromyography (EMG) measures muscle response or electrical activity in response to stimulation of the muscle and is used to identify neuromuscular abnormalities. The neuromuscular abnormalities in Parkinson disease; however, are not in the peripheral neurons, musculature, or neuromuscular junction. Because the disease is limited to the central nervous system, EMG is not an appropriate diagnostic test.

Answer 4: Magnetic resonance imaging in Parkinson disease may show loss of the normal swallow tail appearance in the substantia nigra on axial imaging, but this is not a common finding and is not considered a necessary diagnostic approach for the disease.

Bullet Summary:
Parkinson disease is a clinical diagnosis, arrived at based on a patient's symptoms and physical examination.