Measuring Pain

Lecture 17

Nelson Hendler, MD, MS, Former Assistant Professor of NeurosurgeryJohns Hopkins University School of MedicinePast president-American Academy of Pain Management

Measuring Pain-Can It Be Done?• Pain is a subjective experience• Depression is a subjective experience• Anxiety is a subjective experience• Happiness is a subjective experience• So how is it possible to measure a subjective

experience? • Measure by subjective self reporting• Measure by associated symptoms which are

quantifiable, i.e hours out of bed, or hours of sleep, or weight gain or weight loss, or income

Variables in Measuring Pain• Pain is a subjective experience that can be

perceived directly only by the sufferer. • Pain is a multidimensional phenomenon that can

be described by pain location, intensity, temporal aspects, quality, impact and meaning.

• Pain does not occur in isolation but in a specific human being in psycho-social, economic, and cultural contexts that influence the meaning, experience and verbal and non-verbal expression of pain.

• (National Institutes of Health 1987 p36)

Variables in Measuring Pain• Ethnicity-Cultural-where the expression of pain is

either encouraged or stoic. Harold Merskey, MD• Psychological state of the individual means feelings

which change over time. The best test to measure this is the SCL-90, which asks how a patients feels over the past 5 or 7 days, and how they feel pain

• Psychological traits of the individual means character traits which are fixed and do not change over time, such as obsessive compulsive characteristics, supposedly related to feeling pain

• Genetics-levels of enkephalin and endorphins determine “pain threshold.”

Visual Analogue ScaleIncredibly, this is the Food and Drug Administration (FDA) accepted method of determining the efficacy of a pain relieving medication. The patient is asked to rate his pain, on a 100 mm long line, before receiving the medication, and then the patient takes the medication. After the medicine begins to work, the patient answers how much pain he has, by marking another 100 mm line. The researcher measures how many “mm of pain” the patient had before and after the medication, to determine the effectiveness.

McGill-Melzack • Ron Melzack from McGill, and Warren Torgeson

at Johns Hopkins, recognized that patients used different words to describe their pain.

• Dr. Melzack rank ordered 30 words used to describe the severity of pain, from mild, to nagging to sharp, severe, and excruciating.

• This scale is used to measure the severity of pain….and theoretically measure improvement or worsening over time.

• Melzack failed to recognize that different types of pain fibers have specific types of pain associated with them, i.e. C fibers have sharp pain, etc.

Rat Hot-Plate Test• Pharmaceutical companies measure the efficacy

of early stage pharmaceuticals by the following methods:

• They inject a mouse with a medication, and place the mouse on a hot-plate.

• If the mouse jumps, the interpretation is that the drug has no analgesic properties.

• If the mouse doesn’t jump, they interpret this as the drug is an analgesic, but don’t necessarily consider that the drug may be a sleep inducing drug, paralytic, or ionic flux drug

Petrovich Pain Apperception Test

A patients is shown a series of 17 cards, and has to rank order which pain hurts more, by putting the cards in ascending order. From this sequencing, the physician is theoretically able to determine the pain threshold of the patient, and ability to tolerate pain. The question becomes—to what end?Would you rank the card on the left as hurting more than the card on the right, or the other way around?

5th vital sign• James Campbell, MD past president of the

American Pain Society, felt pain was under-treated, and want medical staff to be aware of the severity of pain in their patients.

• So he implemented asking patients how much pain they had on a scale of 1-5, and considered this the “5th vital sign” along with pulse, blood pressure, weight and height

• Dr Campbell was able to get the “5th vital sign” accepted as a “standard of care” for medical practices and hospital care.

Smiley Face“Smiley Face” is typically used to measure pain in children or semi-literate patients

Ascending and Descending Just Noticeable Differences (JND)

• The Difference Threshold (or "Just Noticeable Difference") is the minimum amount by which stimulus intensity must be changed in order to produce a noticeable variation in sensory experience.

• Ernst Weber (pronouned vay-ber), a 19th century experimental psychologist, observed that the size of the difference threshold appeared to be lawfully related to initial stimulus magnitude. This relationship, known since as Weber's Law.

Weber’s Law

• Weber’s Law can be expressed as:

Weber’s Law• Weber's Law, more simply stated, says that the size of the just noticeable

difference (i.e., delta I) is a constant proportion of the original stimulus value. For example: Suppose that you presented two spots of light each with an intensity of 100 units to an observer. Then you asked the observer to increase the intensity of one of the spots until it was just noticeably brighter than the other. If the brightness needed to yield the just noticeable difference was 110 then the observer's difference threshold would be 10 units (i.e., delta I =110 - 100 = 10). The Weber fraction equivalent for this difference threshold would be 0.1 (delta I/I = 10/100 = 0.1). Using Weber's Law, one could now predict the size of the observer's difference threshold for a light spot of any other intensity value (so long as it was not extremely dim or extremely bright). That is, if the Weber fraction for discriminating changes in stimulus brightness is a constant proportion equal to 0.1 then the size of the just noticeable difference for a spot having an intensity of 1000 would be 100 (i.e., delta I = 0.1 X 1000 = 100).

• Weber's Law can be applied to variety of sensory modalities (brightness, loudness, mass, line length, pain, etc.). The size of the Weber fraction varies across modalities but in most cases tends to be a constant within a specific task modality.

Von Frey Hairs• A von Frey hair is a type of aesthesiometer designed in

1896 by Maximilian von Frey.• These hairs are made from nylon filaments of varying

diameter. The hairs are to be pressed against the skin with enough force so that the hair buckles and forms a U-shape. Given that the force required for this is assumed to be constant, these hairs can be used to apply a very accurate force on specific areas of the skin, thus making von Frey hairs a possible diagnostic, research, and screening tool.

• von Frey hairs are readily used to study skin areas with normal responsiveness, as well as hyper- or hyposensitive areas.

A Von Frey Hair Tool Kit. This tells a physician the relative pressure it takes to feel the hair, and then if the hair is painful. The hair start at a small diameter and ascend to larger ones.

Tourniquet Test- Sternbach• A patient rates their chronic pain as a percent of

unbearable, i.e. “my pain is 50% of unbearable”• A tourniquet is applied to the arm, and the

patient is asked to tell the doctor when the acute pain in the arm equals the pain the patient normally feels, and then tells the doctor when the pain is unbearable, and the tourniquet has to be removed.

• The doctor takes a ratio base on time before the acute pain equals normal chronic pain over time to maximum tolerance, and comparers it to the original estimate. But acute doesn’t equal chonic

Tourniquet Test- Sternbach• So if the patient originally ranked his pain as

50% of unbearable, but after 30 seconds of tourniquet time said the pain from the tourniquet equaled the pain he normally felt and at 2 minutes (120 seconds) said the pain was unbearable, then the doctor would calculate the tested pain as 25% of unbearable, and accuse the patient of exaggerating their pain, because he reported it was 50% of unbearable, before the “objective” tourniquet test, where it was tested to be only 25% of unbearable. (see Sternbach-Pain Patients-Traits and Treatment)

Using Psychological Tests to Measure Pain

• Of all of the misapplications of psychological tests, the MMPI (Minnesota Multiphasic Personality Disorder) test has been the most misapplied.

• Researchers claim they can measure the severity of pain, or presence or absence of pain, based on scores on the MMPI test, which is a 566 question test, with true-false answers, which measure personality traits.

MMPI of “low back losers”• Pilling, Bleumer, and Sternback, based on their

misunderstanding of pain and the MMPI, labeled patients “Pain prone patient,” “pain neurosis,” and “low back loser.”

• They based this on the elevated scales of 1 and 3 (hysteria and hypochondriasis), of the MMPI, and the absence of the elevation of scale 2 (depression).

• This formed the so called “Conversion V” because the graph of the scales has a V in it.

• This is normal in early and late stage chronic pain, but considered pathological by other authors

Example of graphic representation of MMPI scores. Hs is hysteria, D is depression, Hy is hypochondriasis. If all three scales are elevated, and depression is more elevated than Hs, and Hy, then Bleumer calls this a neurotic triad. Hendler calls this a normal response to chronic pain, and Bleumer calls it “pain neurosis.”.

Lees-Haley “Fake Bad Scale” of MMPI• This test has been thrown out of court a number

of times in Florida. • The scale of the MMPI Lees-Haley put together

“diagnoses” plaintiffs as malingering 85% of the time.

• These statistics are not supported by other research, and in fact, are rejected by noted MMPI authorities.

Sims, Dorothy C., “Cross Examining the Psychiatric Expert,” WILG (April 2005): 12-15.Tortter v. Washington Group International, Inc, et al, Case No A466763, Deposition of Paul

Lees-Haley, Vol. 1, taken August 19, 2004Sims, Dorothy C, The Myth of Malingering, Plaintiff Magazine, December, 2007,

Cold Tolerance Test-Ice Water Immersion • This technique uses the same rationale as the

tourniquet test, but instead of “unbearable pain” measured with a tourniquet, ice water is used.

• A patient rates their pain as a percent of unbearable, i.e. my pain is 50% of unbearable

• The patient’s arm is plunged in ice water, and the patient is asked to tell the doctor when the pain in the arm equals the pain the patient normally feels, and then tells the doctor when the pain is unbearable, and the arm has to be removed from the ice water.

Cold Tolerance Test-Ice Water Immersion • The doctor takes a ratio base on time before pain

equal normal pain over time to maximum tolerance, and comparers it to the original estimate.

• If the patient originally ranked his pain as 50% of unbearable, but after 30 seconds in ice water said the pain from the ice water equaled the pain he normally felt and at 2 minutes (120 seconds) said the pain was unbearable, then the doctor would calculate the tested pain as 25% of unbearable, and accuse the patient of exaggerating their pain, because he reported it was 50% of unbearable, before the “objective” ice water test, where it was tested to be only 25% of unbearable.

Lamp Black on Forehead• In the 1940s, a group of doctors at the University of Cornell, led

by Hardy, set out to create a unit of pain intensity. Using the "dol" as a unit, the physicians created a 21-point quantitative scale, from ½ to 10.5 “dols”

• Studies on Pain: A new method for measuring pain threshold, researchers inflicted pain upon subjects using by applying heat to their foreheads for three seconds at a time. 8 dols left 2nd degree burns.

• The intensity of pain increased as researchers increased the heat in each experiment.

• Discrimination of differences in intensity of a pain stimulus as a basis of a scale of pain intensity, with a single dol divided into two "just discernible changes in pain".

Diagnostic Value of Measuring Pain• The severity of pain had no diagnostic value• Since there are so many variables contributing to

the perception of pain from the psychological state of the individual, to the ethnicity, to the biochemistry of the body, the severity of pain is too inconsistent from one individual to another.

• However, the type of pain had diagnostic value. A burning pain suggest neuralgia, and numbness severe neuropathy. A constant pain suggests compression, while an intermittent pain suggests mechanical damage. A throbbing pain is vascular.

Research Value of Measuring Pain• Pain relief is one way researchers quantify the

value of their treatment. • There are many problems using pain relief as a

measure of success, since pain perception is so highly variable.

• Relief measurement of a patient before and after a treatment is more reliable than comparing relief in a group of patients before and after a treatment.

• The best measures are quantifiable indirect measures, such as how much medicine is used.

Pain Validity Test from www.MarylandClinicalDiagnostics.com• The test does not ask about pain severity• Records the impact of pain on the life of the patient• The Pain Validity Test is the only test which has

been proven to have a predictive medical ability• The Pain Validity Test can predict with 95%

accuracy which patient will have a moderate or severe abnormality on at least one correct objective medical test

• The Pain Validity Test can predict with 85% accuracy which patient will not have abnormalities

Pain Validity Test• Pain Validity Test is available on Internet, at

www.MarylandClinicalDiagnostics.com, to validate pain, by predicting the presence or absence of organic pathology.

• It allows a physician to improve diagnostic accuracy, and serves as a screening tool to help get an accurate diagnosis.

• There are 7 articles about the Pain Validity Test, involving 794 patients.

• The test has 32 questions, and takes only 15 minutes to administer & results in 5 min.

• It is available in English and Spanish

Scattergram of Computer Scored Pain Validity Test.On the left, 3* is a severe abnormality, 2 a moderate abnormality, 1 a mild abnormality,

and 0 is no abnormality on at least one objective medical test. At the bottom, 8-25 represent the score on the Pain Validity Test. 17 or less is an Objective Pain Patient, 21

point or higher is an Exaggerating Pain Patient

0

1

2

*3

2118 20178 1210 14 15 1613119 19 22 23 24 25

11/13 = 85%

65/69 = 95%

Objective Pain Patient

Exaggerating Pain Patient

Explanation of the PVT Scattergram• Look at Scattergram- Objective Pain Patients have a 95%

chance of having moderate or severe abnormalities on at least one correct objective measure of organic pathology, such as EMG nerve conduction studies, root blocks, facet block, provocative discograms, MRI, CT, etc.

• Medical articles prove that the MMPI has no predictive medical capabilities. Insurance companies often claim that the MMPI does, but can’t prove it.

• Pain Validity Test can identify patients who will not have medical abnormalities with 85% accuracy.

• In a series of articles, it was reported that only 6%-13% of patients are exaggerating

Available at www.MarylandClinicalDiagnostics.com

Summary• There is little or no diagnostics value to trying

to measure the severity of pain• Measurement of pain is useful for measuring

treatments and outcomes of treatment• Indirectly measuring the impact of pain on a

person’s life is more objective than measuring pain itself

• Knowing the type of pain, and what makes it better or worse, has some diagnostic value

• Psychological traits have no predictive value for the causes of pains