Examination of Pinprick Sensation

By admin On Dec 11, 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 > Sensory Examination > Chapter 29 –
Examination of Pinprick Sensation

Chapter 29

Examination of Pinprick Sensation

PURPOSE

The main purpose of the examination of pinprick
sensation is to localize neurologic pathology by looking for
characteristic distributions of pinprick loss.

WHEN TO EXAMINE PINPRICK SENSATION

Examination of pinprick sensation should be performed on
any patient who has a sensory complaint, such as numbness or tingling.
Pinprick testing should also be performed on most patients with signs
or symptoms of any focal disorder of the central or peripheral nervous
system, because the finding of associated pin loss may aid in
localization. Examination of pinprick sensation otherwise does not need
to be performed routinely in all patients.

NEUROANATOMY OF PIN SENSATION

The pathway for pinprick sensation begins in sensory
nerve endings in the skin, travels up the peripheral nerves to the
dorsal nerve roots to enter the spinal cord and, immediately after
entering, crosses to the other side of the cord and becomes the spinothalamic tract.
The spinothalamic tract ascends the spinal cord and synapses in the
thalamus, where the sensory information for pin sensation is relayed to
the parietal cerebral cortex. In other words, pin sensation felt on the
left side of the body ascends the right side of the spinal cord and
ends up in the right thalamus and right sensory cortex.

EQUIPMENT NEEDED TO TEST PIN SENSATION

A safety pin (preferred) or the point of a broken wooden cotton swab.
Make sure that the pin is fresh from the
factory and has not been used before. It is mandatory that the pin (or
pointed stick) be used only on your one patient, and it should be
discarded in a sharps container after use. Never use a hypodermic
needle to test pin sensation (these are too sharp and draw blood), and
never use any nondisposable pins, such as pins that come screwed into
the top of some reflex hammers.

HOW TO EXAMINE PINPRICK SENSATION

Inform the patient that you’ll be lightly
touching his or her skin with the point of a pin and that it shouldn’t
hurt (because it shouldn’t hurt if you test for pin sensation
correctly). Tell the patient that you will be asking if the pin
sensation feels about the same in terms of “pointedness” in different
areas compared to others. The patient’s eyes can remain open when
assessing pinprick sensation with the method described here.
Lightly touch the area of skin you want
to test with the point of the pin, asking the patient if he or she
feels the “pointedness” of the pin. Never scratch the skin or press
hard enough that it would be truly noxious or draw blood. When
comparing one area of skin to another, ask if the “pointedness is about
the same” or not. If the patient reports a difference in sensation, ask
the patient to describe the difference to you.

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Plan your examination of pin sensation
depending on your diagnostic suspicion, based on your patient’s
symptoms and the preceding and evolving examination findings.
- If you suspect a possible brain,
  thalamic, or brainstem localization of your patient’s symptoms,
  concentrate on detecting side-to-side differences in pin sensation. To
  do this, test pinprick sensation once on one arm, then ask the patient
  if the pin feels about the same as you test the same area of the
  opposite arm to a single pinprick. This can be tested in a few areas of
  one arm (or body) and compared to the other side, checking the
  sensation to an area on one side first and then checking its mirror
  image. Do the same in the lower extremities by testing pin sensation on
  one leg compared to the other.
- If you suspect a spinal cord localization
  of your patient’s symptoms, concentrate on detecting a decrease in
  sensation below a dermatomal level. For example, if you think there is
  a possible thoracic cord localization, march the pin down one side of
  the chest and abdomen by testing single pinpricks scattered inches
  apart while asking the patient if the pointedness feels about the same
  as you go down. Do the same on each side of the chest and abdomen,
  anteriorly and posteriorly.
- If you suspect a nerve root localization,
  concentrate on checking pin sensation within the dermatome of the nerve
  root of concern (depending on the patient’s symptoms), comparing to
  other nerve root distributions. To do this, check the patient’s
  sensation to pinprick within several areas of the extremity (or body)
  that likely belong to the involved dermatome (see Fig. 28-1),
  then ask the patient if the pinprick sensation is about the same or
  different as you assess pinprick in other dermatomes in the same
  extremity and the opposite extremity.
- If you suspect a lesion of a specific
  nerve, concentrate on assessing sensation to pinprick within the
  distribution of that nerve (see Fig. 28-2),
  comparing it to the sensation to pin within areas supplied by other
  nerves of the same extremity and the other extremity, analogous to the
  assessment of nerve root sensory loss.
- If you suspect a polyneuropathy,
  concentrate on checking for a change in sensation in the distal
  extremities compared to the proximal extremities. Because most
  polyneuropathies are worse in the lower extremities, test for distal
  sensory loss by marching the pin down one leg, starting in the calf or
  thigh and proceeding down to the toes. Test with single pinpricks
  spaced a few inches apart as you go down. Make sure that the patient
  can define the pin as “sharp” or “pointed” wherever you start
  proximally, then ask if the pinprick is about the same or less sharp as
  you proceed distally. Do the same test on the other leg.
It is often helpful to assist patients in
their description of a sensory change to pinprick. Patients usually
have little difficulty reporting that the sensation is decreased or
otherwise altered (e.g., tingly or uncomfortable). When they report
that the sensation is decreased, however, you may want to quantify this
to help you determine how clinically significant the decrease is. One
way to do this is to touch the patient with the pin in an area that the
patient has reported as being normal and tell the patient “This is 100%
of pointedness.” Then, touch the patient with the pin in an area that
the patient has reported as having a decrease in sensation and ask
“What percent of pointedness is this?”

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NORMAL FINDINGS

Normally, patients should feel pinprick equally on both
sides of the body, within all cutaneous distributions, and sensation
should be the same distally as proximally.

ABNORMAL FINDINGS

A difference in sensation to pinprick in
one area of the body compared to another is abnormal. This difference
could be a feeling of diminished sensation (hypesthesia or anesthesia)
or other altered sensation (hyperesthesia or dysesthesia). Areas of
diminished sensation are more likely to be of clinical significance the
greater the patient’s subjective quantification of that decrease (i.e.,
a hypesthetic area described as 50% of normal is more likely to be a
significant finding than one described as 90% of normal).
A difference in pinprick sensation of the
extremities or body on one side compared to the other side suggests a
brain, thalamic, or brainstem localization of symptoms. The side of the
body that shows the diminished or altered sensation is the abnormal
side and would be contralateral to the central nervous system lesion.
(Hemi-spinal cord lesions would also cause a unilateral decrease in
pinprick sensation on one side of the body contralateral to the lesion,
but there would also be a loss of posterior column sensation on one
side of the body ipsilateral to the lesion; see Chapter 51, Examination of the Patient with a Suspected Spinal Cord Problem.)
A decrease or other altered sensation to
pinprick below a dermatomal level suggests a spinal cord localization
of symptoms. The dermatomal level where the sensory loss begins to
change represents the patient’s sensory level.
The sensory level found on examination represents the lowest possible
level of the patient’s spinal cord lesion (the actual level of the
lesion might be somewhere above the dermatomal level found; see Chapter 51, Examination of the Patient with a Suspected Spinal Cord Problem).
A decrease or other altered sensation to
pinprick confined to the distribution of a nerve root suggests a nerve
root (radicular) lesion at that level.
A decrease or other altered sensation to
pinprick confined to the distribution of an individual peripheral nerve
suggests a lesion of that nerve.
A decrease or other altered sensation to
pinprick confined to the distal aspects of the extremities suggests a
polyneuropathy. If the distal sensory change is only found in the legs,
this is called a stocking pattern of sensory loss; when more severe, the sensory change may also be found in the distal upper extremities and is called a stocking-glove pattern.

ADDITIONAL POINTS

Another method of pinprick testing
involves asking the patient to discriminate “sharp” from “dull” by
asking the patient to close his or her eyes, then asking the patient if
you are touching the skin with the sharp side (point) of the pin or the
dull side (the side of the safety pin opposite the point). This method
is more time-consuming, and differences between areas can’t as easily
be compared; however, this way to assess pin sensation can be useful as
an adjunct to confirm any sensory loss suggested by the method
described in How to Examine Pinprick Sensation.
Another important modality mediated by
the same pathways as pinprick sensation is the perception of
temperature sensation. Temperature sensation rarely needs to be
assessed, but testing for this modality is helpful in the clinical
assessment of spinal cord lesions, particularly hemi-spinal cord
lesions (the Brown-Séquard syndrome), discussed in Chapter 51, Examination of the Patient with a Suspected Spinal Cord Problem.