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Location, location, location. This is true in real estate and even more so in clinical neurology. Differential building and neurologic decision-making are heavily influenced by the “localization of the lesion.” The lesion is the structure or system that is not functioning correctly.
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Fundamentally, there are 2 primary types of localizations, focal and diffuse (Figure 12-1).
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In a focal lesion, there is a physical change in a specific location (eg, the left corona radiata or the right elbow). If a meningioma grows adjacent to the visual cortex, it will produce visual signs and symptoms. If the same exact tumor grew adjacent to the motor cortex, it would instead produce motor symptoms.
In a diffuse lesion, there is a functional change of a specific system (eg, “the upper motor neurons” or “the peripheral nerves”). Everywhere that system is present, it is likely to not work correctly, but other systems in the same physical place will probably work just fine. If a neurodegenerative disorder targets cerebellar systems, then the patient will show abnormalities everywhere the cerebellar systems are active, including eye movements, speech articulation, swallowing, limb movements, gait, torso balancing, and so on, but will not show any deficits in areas where the cerebellum is not involved.
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PEARL: Wait a second! What about multifocal? True, most neurology texts include multifocal in addition to focal and diffuse. Conceptually, multifocal just means that a patient has more than 1 focal lesion. In each lesion, the location of the lesion, not its nature, is what determines the deficits, rather than the other way around.
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Goals of the Neurologic History
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Obtain the patient’s description of their symptoms, as well as pertinent absent symptoms.
Determine which systems and structures appear to work normally and abnormally.
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Goals of the Neurologic Examination
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Combine the information gathered in the history and examination to decide if the patient’s problems all originate from a particular place (focal) or from a particular system (diffuse).
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When Should I Engage in a Neurologic Examination?
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When patients present with symptoms suggestive of a neurologic problem
When screening for the presence of abnormalities in patients at risk for the development of neurologic disorders
When screening and documenting baseline function of those who are otherwise healthy
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PEARL: This is appropriate for individuals who have no subjective symptoms suggestive of a neurologic problem yet have systemic illnesses that might put them at risk for neurologic dysfunction (eg, patients with diabetes or thyroid disease).