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.
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.Related posts:
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