Overview of the Sensory Examination

Sensory nerve roots supply cutaneous innervation to
specific dermatomes. The dermatome innervation of the extremities is
complex, in part due to the migration of the limb buds during embryonic
development. As a result, the C4-C5 dermatomes abut T1-T2 on the upper
chest, and the L1-L2 dermatomes are close to the sacral dermatomes on
the inner aspect of the thigh near the genitalia. The generally
available dermatomal charts are primarily derived from three sources:
Head and Campbell, Foerster, and Keegan and Garrett, who all used very
different approaches. Figure 26.5 shows the dermatome distributions as
depicted by Keegan and Garrett.

Sensory function is divided clinically into primary
modalities and secondary or cortical modalities. The primary modalities
include touch, pressure, pain, temperature, joint position sense, and
vibration. The cortical or secondary modalities are those that require
synthesis and interpretation of primary modalities by the sensory
association area in the parietal lobe. These include two-point
discrimination, stereognosis, graphesthesia, tactile localization, and
others. When the primary modalities are normal in a particular body
region, but the cortical modalities are impaired, a parietal lobe
lesion may be responsible. Itch and tickle sensations are closely
allied to pain; they are probably perceived by the same nerve endings
and are absent following procedures used for the relief of pain.

Many terms have been used, not always consistently, to
describe sensory abnormalities. The definition of esthesia is
perception, feeling, or sensation (Gr. aesthesis “sensation”). Algesia refers to the sense of pain (Gr. algos
“pain”). Hypalgesia is a decrease, and analgesia (or analgesthesia) an
absence, of pain sensation. The combining form “algia” refers to any
painful condition. Hypesthesia is a decrease, and anesthesia an
absence, of all sensation. Paresthesia is an abnormal sensation;
dysesthesia (Gr. dys “bad”) is an abnormal, unpleasant, or painful sensation. Table 22.1 summarizes some of the definitions.

Sensory abnormalities may be characterized by an
increase, decrease, absence, or perversion of sensation. An example of
increased sensation is pain—an unpleasant or disagreeable feeling that
results from excessive stimulation of certain sense organs, fibers, or
tracts. Perversions of sensation take the form of paresthesias,
dysesthesias, and phantom sensations. Impairment and loss of sensation
result from decreased acuity of the sensory organs or receptors,
impaired conduction in sensory fibers or tracts, or dysfunction of
higher centers causing impairment in the powers of perception or
recognition.

The sensory examination is performed to discover whether
areas of absent, decreased, exaggerated, or perverted sensation are
present, and to determine the type of sensation affected, the degree of
abnormality, and the distribution of the abnormality. Findings may
include loss, decrease, or increase of one or more types of sensation;
dissociation of sensation with loss of one modality type but not of
others; loss of ability to recognize differences in degrees of
sensation; misinterpretations (perversions) of sensation; or areas of
localized hyperesthesia. More than one of these may occur
simultaneously.

The sensory examination is arguably the most difficult
and tedious part of the neurologic examination. Some examiners prefer
to assess sensory functions early in the course of the examination,
when the patient is most likely to be alert and attentive. Fatigue
causes faulty attention and slowing of the reaction time, and the
findings are less reliable when the patient has become weary during the
examination. Others argue the routine sensory examination is the most
subjective and least useful part of the neurologic examination, and
prefer to leave it until the end. Since the results depend largely on
subjective responses, the full cooperation of the patient is necessary
if conclusions are to be accurate. Occasionally, objective evidence,
such as withdrawal of the part

stimulated,
wincing, blinking, and changes in countenance, may aid in the
delineation of areas of sensory change. Pupillary dilation,
tachycardia, and perspiration may accompany painful stimulation.
Keenness of perception and interpretation of stimuli differ in
individuals, in various parts of the body, and in the same individual
under different circumstances.

For a reliable sensory examination, the patient must
understand the procedure and be ready and willing to cooperate.
Accurate communication is vital. The purpose and method of testing
should be explained in simple terms, so that the patient understands
the expected responses. During the examination the patient should be
warm, comfortable, and relaxed. The best results are obtained when the
patient is lying comfortably in a warm, quiet room. Obtaining patient
confidence is important. Satisfactory results cannot be obtained when
the patient is suspicious, in pain, uncomfortable, fearful, confused,
or distracted by sensations such as noise or hunger. If the patient is
in pain or discomfort, or if he has recently been sedated, the
examination should be postponed. The areas under examination should be
uncovered but it is best to expose the various parts of the body as
little as possible. The patient’s eyes should be closed or the areas
under examination shielded to eliminate distractions and to avoid
misinterpretation of stimuli. Homologous areas of the body should be
compared whenever possible.

The detail and technique used for the sensory
examination depend on the history. For example, a patient with no
sensory complaints referred for evaluation of headache or vertigo
requires only a screening examination. A patient who is seen for
possible carpal tunnel syndrome, radiculopathy, peripheral neuropathy,
or a suspected parietal lobe lesion requires a very different approach.

The examiner should first determine whether the patient
is aware of subjective changes in sensation or is experiencing abnormal
spontaneous sensations. Sensory symptoms may be divided into negative
symptoms, lack of sensation, and positive symptoms, abnormal sensory
discharges such as paresthesias and dysesthesias. Positive and negative
symptoms may occur together. Inquire whether the patient has noticed
pain, paresthesias, or loss of feeling; whether any part of the body
feels numb, dead, hot, or cold; whether he has perceived sensations
such as tingling, burning, itching, “pins and needles,” pressure,
distention, formication, or feelings of weight or constriction. If such
symptoms are present, determine their type and character, intensity,
distribution, duration, and periodicity, as well as exacerbating and
relieving factors. Spontaneous pain must be differentiated from
tenderness. Pain and numbness may exist together, as in thalamic pain
and peripheral neuropathy. The patient’s manner of describing the pain
or sensory disturbance and the associated affective responses, the
nature of the terms used, the localization, and the precipitating and
relieving factors may aid in differentiating between organic and
nonorganic disturbances. Nonorganic abnormalities are often associated
with inappropriate affect (either excessive emotionality or
indifference), are often vague in character or location, and reactions
to them are not consistent with the degree of disability.

If the patient has no sensory symptoms, testing can be
done rapidly, bearing in mind the major sensory nerve and segmental
supply to the face, trunk, and extremities. In certain situations, more
careful sensory testing is required. If there are specific sensory
symptoms; motor symptoms such as atrophy, weakness, or ataxia; or if
any areas of sensory abnormality are detected on the survey
examination; or if the clinical situation suggests the likelihood of
sensory abnormalities; then detailed sensory examination should be
performed. The presence of trophic changes, especially painless ulcers
and blisters, is also an indication for careful sensory testing, since
these may be the first manifestations of a sensory disorder of which
the patient is unaware. In patients with limited cooperation, it may be
desirable to examine the areas of sensory complaint first and then
survey the rest of the body.

The simpler the method of examination, the more
satisfactory the conclusions. Explain to the patient what is to be done
and demonstrate in an area expected to be normal what the stimulus
feels like. Then have the patient close his eyes and begin the testing.
The subject should be asked to tell the type of stimulus perceived and
its location, with the examiner taking care not to suggest responses.
Responses are normally prompt, and a consistent delay in answering may
indicate an abnormal delay in perception. There are two general
screening patterns: side to side and distal to proximal. The
side-to-side screening should usually compare the major dermatomes and
peripheral nerve distributions, although more abbreviated screening may
be appropriate in certain clinical circumstances. Distal to proximal
testing is appropriate when peripheral neuropathy is part of the
differential diagnosis. The distribution of abnormalities can be drawn
on the skin with a marker and recorded on a chart, indicating areas of
change in the various modalities by horizontal, vertical, or diagonal
lines, stippling, or different colors. A key helps to explain the
meaning of the various symbols and colors, as does a note regarding the
cooperation and insight of the patient and an estimate of the
reliability of the examination. Sensory charts are helpful for
comparison with the results of subsequent examinations in following the
course of the patient’s illness, and for comparison with the results of
other examiners.

Accuracy in localization of pain, temperature, and
tactile stimuli is also informative. Tactile localization is a
sensitive test of sensory function; there may be loss of localization
before there is a detectable change in sensory threshold. Tactile
localization is most accurate on the palmar surfaces of the fingers,
especially the thumb and index finger. The patient should name or point
to the area stimulated, comparing responses on the two sides of the
body.

The results of the sensory examination may at times seem
unreliable and confusing. The process can become tedious, and the
findings difficult to interpret. Sensory changes due to suggestion are
notoriously frequent in emotionally labile individuals, but suggestion
can produce nonorganic findings in patients with organic disease. Care
must be taken in drawing conclusions. To obtain reliable results, it
may be necessary to postpone the sensory examination if the patient has
become fatigued, or to repeat the testing at a later time. The sensory
examination should always be repeated at least once to confirm the
findings. Sensory testing, more than any other part of the neurologic
examination, requires patience and detailed observation for reliable
interpretation.

The following are some of the difficulties that may be
encountered in performing the sensory examination. The uncooperative
patient may be indifferent to the sensory examination or object to the
use of painful stimuli. The overly cooperative patient, on the other
hand, may make too much of small differences and report changes that
are not present. Some areas of the body, such as the antecubital
fossae, the supraclavicular fossae, and the neck, are more sensitive
than others; apparent sensory changes in these regions may lead to
fallacious conclusions. The last in a series of identical stimuli may
be interpreted as the strongest. Even though pain sensibility is
absent, a patient may still be able to identify a sharp stimulus with a
pin. Occasionally in syringomyelia, with lost pain but preserved
tactile sensibility, the patient may recognize the pin point in an
analgesic area and give confusing and inconsistent responses. Sensory
findings are difficult to evaluate in individuals with low intellectual
endowment, language difficulties, or a clouded sensorium, but it may be
necessary to carry out the examination despite these obstacles. In
patients with altered mental status or a decreased sensorium, pain may
be tested grossly by pricking or pinching the skin, comparing responses
on the two sides of the body. In such patients, it may only be possible
to determine whether or not the patient reacts to painful stimuli in
various parts of the body. A child may be fearful of testing, requiring
assurance at the outset that the examination will be brief and not
actually painful. In young children, it is often best to delay sensory
testing until the end of the examination, particularly when even mildly
uncomfortable, yet threatening, stimuli are applied. This may also hold
true for some apprehensive adults.