There are many methods for testing superficial pain sensation. A simple and commonly used method, as reliable as any, is to use a common safety pin bent at right angles so its clasp may serve as a handle. The instrument should be sharp enough to create a mildly painful sensation, but not so sharp as to draw blood. A hypodermic needle is far too sharp unless its point has been well blunted against some hard surface. A broken wooden applicator stick is often used, and is usually satisfactory provided the shards are sharp. Adequately sharp ends can be obtained by holding the stick at the very ends while breaking it. Disposable sterile devices, sharp on one end and dull on the other, are commercially available. While it is not necessary for the stimulating instrument to be sterile, whatever is used must be discarded after use on a single patient to avoid the risk of transmitting disease from accidental skin puncture. A helpful trick is to hold the pin or shaft of the applicator stick lightly between thumb and fingertip, and let the shaft slide between fingertip and thumb tip with each stimulation. This helps insure more consistent stimulus intensity than putting a fingertip on the end of the instrument and trying to control the force with the hand or wrist. Experience teaches how to gauge the intensity of the applied stimulus and the expected reaction to it.

It is best to do the examination with the patient’s eyes closed. The patient should be asked to judge whether the stimulus feels as sharp on one side as on the other. Always suggest the stimuli should be the same, as by language such as, “Does this feel about the same as that?” Avoid such language as “Does this feel any different?” or “Which feels sharper?” Suggesting there should be a difference encourages some patients to overanalyze and predisposes them to spurious findings and a tedious, often unreliable examination. A commonly used technique is asking the patient to compare one side to the other in monetary or percentage terms, for example, “If this (stimulating the apparently normal side) side is a dollar’s worth (or 100%), how much is this (stimulating the apparently abnormal side) worth?” The overanalytical but neurologically normal patient often responds with an estimate on the order of “95 cents,” while the patient with real, clinically significant sensory loss is more apt to respond with “5 cents” or “25 cents.” Delivering alternately sharp and dull stimuli, as with the sharp and blunt ends of a safety pin, and instructing the patient to
reply “sharp” or “dull” is frequently useful but may not detect subtle sensory loss only detectable in comparison with an uninvolved area. Slight changes can sometimes be demonstrated in a cooperative patient by asking her to indicate the alterations in sensation when a pinpoint is drawn lightly over the skin. A cooperative patient with a discrete distribution of sensory loss may be able to map out the involved area quite nicely if instructed how to proceed and left alone for a short time with tools and a marking instrument. The affected area can then be compared with a figure showing sensory distributions.