Approach to the Motor Examination

By admin On Jun 7, 2023

Ovid: Field Guide to the Neurologic Examination

Authors: Lewis, Steven L.

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

> Table of Contents > Section 2
– Neurologic Examination > Motor Examination > Chapter 24 –
Approach to the Motor Examination

Chapter 24

Approach to the Motor Examination

PURPOSE

The purpose of the motor examination is to localize
neurologic pathology by looking for characteristic distributions of
muscle weakness.

WHEN TO EXAMINE MOTOR FUNCTION

Examination of muscle strength is an essential part of
all neurologic examinations and is particularly important in the
examination of patients who present with a complaint of weakness. The
choice and extent of muscles to be tested should be dictated by the
clinical scenario; for example, the muscles that should be examined in
a patient in a screening neurologic examination would differ from that
of a patient who complains of weakness in an extremity. The assessment
for drift of the outstretched arms (see Chapter 25,
Examination of Upper Extremity Muscle Strength) should also be
performed routinely. Muscle tone, a component of the motor examination
that does not need to be assessed in all patients but is helpful in
many situations, is described in Chapter 27, Examination of Tone.

NEUROANATOMY OF THE MOTOR EXAMINATION

The pathway for muscle movement begins in nerve
cells—the upper motor neurons—located on the precentral gyrus of each
frontal lobe. The axons from these nerve cells become the corticospinal
tracts, which travel through the internal capsule and into the
brainstem; each corticospinal tract then crosses in the low medulla to
the opposite side and continues downward through the spinal cord.
Within the spinal cord, the corticospinal tracts on each side synapse
with nerve cells in the anterior horns of the ipsilateral spinal cord
gray matter. Axons from these second-order neurons—the lower motor
neurons—leave the spinal cord as the cervical, thoracic, or lumbosacral
nerve roots. The nerve roots in the extremities become the brachial or
lumbosacral plexus and then the peripheral nerves, which innervate
muscles through the neuromuscular junction.

EQUIPMENT NEEDED TO TEST MUSCLE STRENGTH

None.

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TABLE 24-1 Grading of Muscle Strength

Grade	Definition
0	Complete paralysis of a muscle
1	Just a trace of muscle movement
2	Muscle movement that cannot overcome the resistance of gravity
3	Muscle can move against gravity but cannot overcome any other resistance
4	Muscle is weak but can move against gravity and additional resistance
5	Normal muscle strength

HOW TO EXAMINE MUSCLE STRENGTH

Inspect the muscles for atrophy or fasciculations.
Test muscle strength one muscle at a
time. It’s usually best to test the muscle on one side first and then
the other side to assess for symmetry. When weakness on one side is
suspected, test the muscle on the strong side before testing the weak
side. Sometimes, particularly when focal weakness is not suspected,
it’s reasonable to test the strength of the same muscles on both sides
simultaneously.
For each muscle to be tested, ask the
patient to hold the limb in the optimal position for testing of that
muscle, and instruct the patient to do his or her best to resist as you
pull or push in the opposite direction of the action of that muscle, as
illustrated and described in Chapter 25, Examination of Upper Extremity Muscle Strength, and Chapter 26, Examination of Lower Extremity Muscle Strength.
Grade the strength of each muscle on a scale of 0 (weakest) to 5 (strongest). Table 24-1 summarizes the definition of the grading scale for muscle strength testing.
Report the strength of each muscle as its
grade out of 5. For example, a muscle with a grade of 4 is reported as
4 out of 5 and is written as 4/5 or, often, simply 4.

NORMAL FINDINGS

Normally, there should be no atrophy or fasciculations
of the muscles. Strength should be full (5/5) and symmetric in all
muscles tested of the arms and legs.

ABNORMAL FINDINGS

Inspection of the Muscles

Muscle atrophy or fasciculations (visible involuntary
twitches of the muscle) are abnormal and suggest dysfunction of the
lower motor neuron supplying that muscle; this can occur from a lesion
occurring at or anywhere distal to the anterior horn cell, including
the motor nerve root, plexus, or peripheral nerve.

Muscle Strength Testing

Any muscle strength that is less than 5/5 is abnormal. Table 24-2 summarizes the common terminology used to describe muscle weakness.

Muscle weakness can occur due to upper
motor neuron (corticospinal tract) or lower motor neuron dysfunction
from lesions located anywhere along the motor pathway from the cerebral
cortex to the muscles themselves.

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TABLE 24-2 Terminology Used to Describe Muscle Weakness

Terminology	Definition
–plegia (suffix)	Paralysis of a muscle or a limb (0/5)
–paresis (suffix)	Weakness less severe than complete paralysis (1/5 to 4/5)
Hemiparesis and hemiplegia	Weakness of the arm and leg on one side of the body
Quadriparesis and quadriplegia (sometimes called tetraplegia)	Weakness of both arms and both legs
Paraparesis and paraplegia	Weakness of both legs

Use the distribution of any weakness you discover to help determine the most likely localization of the patient’s pathology (Table 24-3).
As you proceed with the rest of the
examination, look for further clues to support or refute your
hypothesis regarding the localization of the cause of the patient’s
weakness, such as the distribution of sensory findings (if any) and the
presence or absence of any upper or lower motor neuron signs on reflex
testing (see Chapter 36, Approach to Reflex Testing).

ADDITIONAL POINTS

Although the motor grading scale is easy
to understand and use, there’s still a significant subjective component
to it. There may be significant interphysician and intraphysician
variability in muscle grading, even of the same patient.

Many clinicians like to add a + or a –
sign to the muscle grade (for example, 4-) to imply subtle additional
distinctions in muscle strength. Be

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aware, however, that many clinicians add the + sign to all
whole number muscle grades when reporting muscle strength—that is, all
muscles with a grade of 4 are written as a 4+. In this situation, only
the – sign implies a specific distinction.

TABLE 24-3 Lesion Localization Suggested by the Distribution of Weakness

Distribution of Weakness	Localization Suggested
Arm and leg on one side of body (hemiparesis)	Contralateral brain or brainstem
Both arms and both legs (quadriparesis)	Cervical cord (myelopathy), bilateral hemispheres or brainstem, or diffuse neuromuscular process
Both legs (paraparesis)	Spinal cord or cauda equina (or, less likely, both frontal lobes)
Proximal arms and legs	Muscle disease (myopathy) or other diffuse neuromuscular process
Distal arms and legs	Diffuse neuropathic process (polyneuropathy)
Muscles supplied by one nerve root	Nerve root (radiculopathy)
Muscles supplied by portion of brachial or lumbar plexus	Plexus (plexopathy)
Muscles supplied by single peripheral nerve	Single nerve trunk (mononeuropathy)
Muscles supplied by several individual peripheral nerves	Multiple nerve trunks (mononeuropathy multiplex)

When testing muscle strength, don’t be
overzealous and wrestle with the patient. It doesn’t take a great deal
of resistance or power on your part to determine that muscle strength
is normal or abnormal or to distinguish a 3 from a 4.
Save any designation of less than 5 for
true muscle weakness and not the giveaway of muscle strength that can
occur, for example, due to discomfort or bony or joint pathology. Also,
don’t grade a patient’s normal muscle strength at less than a 5 simply
because you are bigger, younger, or stronger than the patient. Most
elderly patients, for example, are 5 out of 5 in all muscle groups,
unless they have a neurologic problem causing focal or diffuse weakness.