Approach to Reflex Testing

By admin On Dec 14, 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 2
– Neurologic Examination > Reflex Examination > Chapter 36 –
Approach to Reflex Testing

Chapter 36

Approach to Reflex Testing

PURPOSE

The purpose of testing reflexes is to localize
neurologic pathology to the central or the peripheral nervous system by
looking for evidence of upper motor neuron or lower motor neuron (or
peripheral sensory nerve) dysfunction.

WHEN TO TEST REFLEXES

Testing of muscle stretch reflexes and testing for the
Babinski sign should be performed on all patients as part of a standard
neurologic examination.

NEUROANATOMY OF REFLEXES

The muscle stretch reflexes and the Babinski sign are
spinal reflexes. In both of these reflexes, the stimulus sends an
afferent (sensory) impulse up a sensory nerve into the dorsal root of
the spinal cord, which completes the reflex arc by ultimately synapsing
on motor neurons within the spinal cord, causing an efferent (motor)
response. The corticospinal tract (the upper motor neuron) has an
inhibitory influence on the muscle stretch reflexes and the Babinski
sign.

EQUIPMENT NEEDED TO TEST REFLEXES

A reflex hammer to test muscle stretch reflexes (see Chapter 37, Examination of the Muscle Stretch Reflexes)
A blunt object to test for the Babinski sign (see Chapter 38, Testing for the Babinski Response)

HOW TO TEST REFLEXES

See Chapter 37, Examination of the Muscle Stretch Reflexes, and Chapter 38, Testing for the Babinski Response, for testing discussion.

NORMAL FINDINGS

Normally, patients should have intact but not severely
hyperactive muscle stretch reflexes. There should also be no Babinski
sign in either foot.

ABNORMAL FINDINGS

There are two main kinds of abnormal findings that can
be seen on reflex testing: findings due to the loss of the normal
inhibitory influence of the upper motor neuron on the reflexes and
findings due to lesions of the lower motor neuron or sensory nerve
affecting the reflex arc itself.

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TABLE 36-1 Interpretation of Abnormal Reflexes

Reflex Finding		Localization of Dysfunction Primarily Suggested
Hyperactive muscle stretch reflexes
	Diffuse hyperreflexic muscle stretch reflexes	Bilateral hemisphere or brainstem
	Diffuse hyperreflexic muscle stretch reflexes	Bilateral upper cervical spinal cord
	Unilateral hyperreflexic muscle stretch reflexes	Unilateral (contralateral) hemisphere or brainstem
		Unilateral (ipsilateral) spinal cord
	Hyperreflexic muscle stretch reflexes only in the legs	Thoracic spinal cord (cervical cord still possible)
Hypoactive muscle stretch reflexes
	Diffuse areflexic (or severely hyporeflexic) muscle stretch reflexes	Polyneuropathy or polyradiculopathy
	Distal absence of muscle stretch reflexes (e.g., absent ankle jerks)	Polyneuropathy
	Single absent muscle stretch reflex	Radiculopathy
Babinski sign
	Bilateral Babinski signs	Bilateral hemisphere, brainstem, or spinal cord
	Unilateral Babinski sign	Unilateral (contralateral) hemisphere or brainstem
		Unilateral (ipsilateral) spinal cord

Abnormalities due to Upper Motor Neuron (Corticospinal Tract) Dysfunction: Hyperreflexia and the Babinski Sign

The corticospinal tracts are the upper
motor neurons. Abnormalities on reflex testing that occur as a result
of corticospinal tract dysfunction are called upper motor neuron signs,
and they can occur due to any cause of corticospinal tract dysfunction
anywhere along their course, from their origin as neurons in the motor
cortex to their descent in the spinal cord. These upper motor neuron
signs occur due to the loss of the normal inhibitory influence that the
corticospinal tract has on the muscle stretch reflexes, which therefore
become hyperactive (hyperreflexic), and the loss of the normal inhibitory influence that the corticospinal tract has on the Babinski sign, which results.
In addition to muscle stretch reflex hyperreflexia and the Babinski sign, other upper motor neuron findings can include clonus
(a severe form of muscle stretch reflex hyperreflexia) and increased
tone (stiffness) due to spasticity in the involved limbs (see Chapter 27,
Examination of Tone). Upper motor neuron signs are usually, but not
invariably, also accompanied by weakness in the involved extremities.

Abnormalities due to Dysfunction of the Reflex Arc Itself: Hyporeflexia

Dysfunction of either the lower motor
neuron (efferent) or sensory (afferent) components of the reflex arc
may cause diminished (hyporeflexic) or absent (areflexic) muscle
stretch reflexes in the involved extremities. Depending on the cause
and severity of the process, the diminished reflexes may be accompanied
by weakness (due to lower motor neuron dysfunction), sensory loss, or
even hypotonia in the involved extremity.

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Table 36-1
summarizes the potential localizations suggested by the distribution of
abnormal reflexes. More information regarding the interpretation of
these abnormal reflexes can be found in Chapter 37, Examination of the Muscle Stretch Reflexes, and Chapter 38, Testing for the Babinski Response.