Localization of Neurologic Disease

By admin On Dec 8, 2024

Ovid: Field Guide to the Neurologic Examination

Authors: Lewis, Steven L.

Title: Field Guide to the Neurologic Examination, 1st Edition

> Table of Contents > Section 1
– Neurologic Diagnosis: General Considerations > Chapter 2 –
Localization of Neurologic Disease

Chapter 2

Localization of Neurologic Disease

PURPOSE OF NEUROLOGIC LOCALIZATION

The purpose of neurologic localization—an essential
component of neurologic diagnosis—is to determine where in the nervous
system the patient’s dysfunction is occurring, paving the way for the
second key element of neurologic diagnosis, the determination of the
mechanism of that dysfunction (see Chapter 3, Mechanisms of Neurologic Disease).

WHEN TO PERFORM NEUROLOGIC LOCALIZATION

Neurologic localization needs to be performed in every
patient who presents with a symptom that is potentially due to nervous
system dysfunction. Localization is often not hard, especially if you
initially think in terms of the gross neuroanatomic areas described in
this chapter and don’t try to overcomplicate things. Neurologic
localization is a thought process that should occur during and after
every neurologic history and during and after every neurologic
examination.

NEUROANATOMY OF NEUROLOGIC LOCALIZATION

Neurologic disease can occur due to dysfunction anywhere
within the central or peripheral nervous system. The nervous system can
be divided into eight major areas as listed in Box 2-1, and these are
the regions to which you should initially try to localize neurologic
disease. Although narrower localization is clearly optimal (i.e., where
in the brain or spinal cord is the problem?), you’ve made a lot of
headway if you can decide in which of these eight major areas your
patient’s problem most likely resides.

The diagnostic importance of the ability to localize
your patient’s neurologic dysfunction to one of these gross
neuroanatomic regions should not be underestimated. Table 2-1 summarizes some of the diagnostically relevant functions of these eight regions of the nervous system; in Table 2-1, the brain (cerebral hemispheres) is subdivided into the cerebral hemispheric cortex and the deep cerebral hemisphere.

EQUIPMENT NEEDED TO LOCALIZE NEUROLOGIC DISEASE

None (other than the equipment used for the neurologic examination—localization is a thought process).

HOW TO LOCALIZE NEUROLOGIC DISEASE

Localization is based on the symptoms obtained from the
history and the signs found during the neurologic examination. The
process of localization consists of deciding which area of nervous
system dysfunction best explains these symptoms and signs based on
knowledge of the function of these regions. Table 2-2
summarizes some symptoms and signs that are helpful in localizing
neurologic disease to the general regions of the nervous system.

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These
principles and the use of signs and symptoms to further narrow the
regions of localization are described in greater detail throughout this
book.

BOX 2-1 General Locations of Nervous System Disease

Central Nervous System

Brain (cerebral hemispheres)^a

Brainstem

Cerebellum

Spinal cord

Peripheral Nervous System

Nerve root

Peripheral nerve^b (including most cranial nerves^c)

Neuromuscular junction

Muscle

^a
Although the brainstem and cerebellum are technically part of the
brain, most clinicians think of “the brain” as the cerebral hemispheres
without the brainstem and cerebellum.

^b The brachial plexus and the lumbar plexus would be included within the “peripheral nerve” localization.

^c
Most of the cranial nerves are peripheral nerves, except for cranial
nerves I and II, which are actually extensions of the central nervous
system.

NORMAL FINDINGS

Patients without neurologic disease have nothing to localize.

ABNORMAL FINDINGS

The abnormal finding on neurologic localization is the
region of localization itself. During the diagnostic process, the
localization can be reported broadly (e.g., left hemisphere or spinal
cord) or narrowly (e.g., left temporal lobe or cervical spinal cord) as
you feel is most appropriate given the clues from the history and
examination and the outcome of investigations.

TABLE 2-1 Simplified Listing of Some Diagnostically Relevant Functions of the Major Regions of the Nervous System

Region	Some Major Functions of the Region
Brain (hemispheric cortex)	Thought, language, memory, visual perception of contralateral space, contralateral motor and sensory function
Brain (deep cerebral hemisphere)	Contralateral motor and sensory function
Brainstem	Eye movements, motor and sensory function of face and body, alertness, sensation of nausea, coordination of extremities, balance
Cerebellum	Coordination of extremities, balance
Spinal cord	Motor and sensory function of the body and extremities, bowel and bladder control
Nerve root	Motor and sensory function in territory of nerve root
Peripheral nerve (or cranial nerve)	Motor and sensory function in territory of nerve or cranial nerve
Neuromuscular junction	Motor function of extremities, eye movements, swallowing, breathing
Muscle	Motor function

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TABLE 2-2 Characteristic Symptoms and Signs of Neurologic Disease at Different Major Locations

General Location	Characteristic Symptoms and Signs Suggestive of Localization to This Region^a
Brain (hemispheric cortex)	Cognitive dysfunction Speech and language dysfunction Hemiparesis Hemisensory loss Visual field deficits Headache Upper motor neuron signs
Brain (deep hemisphere)	Hemiparesis Hemisensory loss Headache Upper motor neuron signs
Brainstem	Diplopia, dysarthria, nausea, vomiting, vertigo Alterations in level of consciousness Ataxia of gait or extremities Unilateral or bilateral weakness or sensory loss Crossed hemiparesis (e.g., weakness on one side of the face and the opposite side of the body) Crossed hemisensory loss (numbness on one side of the face and the opposite side of the body) Upper motor neuron signs
Cerebellum	Ataxia of gait or extremities Dysarthria, nausea, vomiting, vertigo Headache
Spinal cord	Bilateral weakness and sensory loss Bowel and bladder dysfunction Brown-Séquard syndrome (see Chapter 51, Examination of the Patient with a Suspected Spinal Cord Problem)
	Upper motor neuron signs
Nerve root	Radiating pain corresponding to a nerve root distribution Numbness or weakness in a nerve root distribution Diminished reflex (lower motor neuron signs) in territory of nerve root
Peripheral nerve	Distal paresthesias, sensory loss, or weakness Diminished distal reflexes (distal lower motor neuron signs)
Neuromuscular junction	Waxing and waning weakness, dysarthria, dysphagia, ptosis, diplopia
Muscle	Weakness (especially proximal)
^a Not all lesions in these locations produce these symptoms and signs; however, the finding of these symptoms and signs would be consistent with this localization.

Some areas of localization have their own neurologic
terminology to describe them. These useful terms, which are listed and
defined in Table 2-3, are helpful in
categorizing sites of neurologic dysfunction. Because these terms are
generic and only imply broad localization, a causative process is not
implied; the only implication is that there is pathology of some sort
(hence the suffix –opathy) involving that structure.

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TABLE 2-3 Common Terms Used to Describe Localizations of Neurologic Dysfunction

Term	Meaning	Origin of Prefix	Comments
Encephalopathy	Disease of brain	Encephalo: brain	Refers to diffuse, not focal, brain dysfunction
Myelopathy	Disease of spinal cord	Myelo: spinal cord	Refers to any cause of spinal cord dysfunction
Radiculopathy	Disease of nerve root	Radiculo: root	Refers to any cause of nerve root dysfunction
Neuropathy	Disease of nerve	Neuro: nerve	Refers to any cause of nerve dysfunction
Myopathy	Disease of muscle	Myo: muscle	Refers to any cause of muscle dysfunction

ADDITIONAL POINTS

Localization is the key to neurologic diagnosis; it’s why we’re taught neuroanatomy in medical school.
The neuroanatomy that you need to know to
localize neurologic disease is not really that much (less than what you
were taught in medical school)! The important basic pathways (and
shortcuts) that you need to know for neurologic localization and for
understanding the role of each component of the examination are
described throughout this book.