Fibromyalgia Pain Characteristics

Pain Characteristics

Pain Quality

The McGill Pain Questionnaire (MPQ) 35,70. can provide information on the characteristics of pain in FMS by use of inquiry into 78 "pain" adjectives, which are divided into four major categories: sensory (e.g., hot, burning, scolding, searing); affective (e.g., fearful, frightening, terrifying); evaluative (e.g., annoying, troublesome, miserable, intense, unbearable); and miscellaneous sensory (e.g., cool, cold, freezing). A pain rating index can be obtained, based on the ranked value of each description for the four categories, both individually and combined. As this index takes 10 to 15 minutes to complete, a short form MPQ (SF-MPQ) has been validated. This consists of 15 adjectives (11 sensory, 4 affective) taken from the large MPQ. These are rated on a scale from O= none to 3 = severe pain."

Table 1. CLINICAL ASSESSMENT OF PAIN

Characteristic Instrument (examples)
Quality McGill Pain Questionnaire
Severity McGill Pain Questionnaire
  Visual Analog Scale
  Verbal Rating Scale
Distribution Pain Diagram
Threshold Digital Palpation
  Dolorimeter
  Myalgic Scores
Tolerance Dolorimetry
Behavior Direct-observation
  Indirect-Illness Behavior
  Questionnaire
Modulation Observation

 


Pain Severity

Alternatively, a verbal rating scale may be used whereby the patient is asked to grade overall severity of the pain by choosing among words that describe it. These words form an ordinal scale. Pain may be assessed in isolation (e.g., none, mild, moderate, severe) or in relation to a previous evaluation (e.g., better, unchanged, worse)." Perhaps the most convenient and commonly used method to assess pain severity is with a visual analogue scale (VAS). A 100 mm horizontal line is shown with a statement such as "no pain" at one end and "pain as bad as it could be" at the other end. The subject is asked to mark the point corresponding to his or her pain at a particular time or during an interval, such as the past 24 hours or past week. The distance in millimeters from one end is used as the result in most studies. VAS scores are reproducible and correspond with verbal rating scales and the MPQ. Transformation to normalize the data or use of nonparametric statistical analysis is required."

The pain subscale of the Arthritis Impact Measurement Scale (AIMS) instrument can be used as a measure of pain for patients with FMS. A number of other instruments have been used to define aspects of pain measurement." It is emphasized that choice of instrument needs to be tailored to the clinical situation under consideration.

Pain Distribution

Pain distribution may be indicated on a pain diagram. Such diagrams are often included in assessment of a patient with FMS. For instance, the MPQ" incorporates a body outline on which a subject can indicate the location of their pain. No formal assessment of drawings from this questionnaire appears in the literature. Pain diagrams are incorporated in the Clinical Health Assessment Questionnaire (CLINHAQ) and body area (scored O-l) may be summed for a Body Pain Index. Various templates have been tested for scoring such a diagram."

Pain Threshold General Comments

Pain threshold is the first barely perceptible pain to appear in a instructed subject under given conditions of noxious stimulation. Related to pain threshold are the descriptors hyperalgesia, meaning increased pain response to a stimulus that is normally painful, and allodynia, pain induced by a stimulus that does not normally cause pain. FMS subjects have a lowered pain threshold and thus have hyperalgesia. Allodynia accompanies this change. When the pain complaint is widespread, there is generalized hyperalgesia in FMS subjects compared with asymptomatic subjects. 43, 73, 85, 94, 98. The same situation holds when there is localized pain complaint with accompanying localized hyperalgesia. 43, 44.

Pain threshold may be assessed using thermal, chemical, or mechanical noxious stimuli. Most studies use pressure to measure pain threshold (PPT). Digital palpation is the most widely used technique; in this method, the force needed to blanch the fingernail of the thumb is the appropriate pressure to use on the "tender point" sites to establish whether this constitutes a painful stimulus. The American College of Rheumatology (ACR) classification criteria use this methodology." Algometry, using a dolorimeter, is also used. Two common dolorimeters, the Chaitollon (Chaitollon Instruments, Kew Gardens, NY) and the Fischer [Pain Diagnostics and Thermography, Great Neck, NY], are force gauges that measure the amount of pressure applied to a specific location. These instruments differ in the cross-sectional area of the foot pad applied to the site to be tested; the former instrument has 1.54 cm2 of surface area, and the latter has 1 cm2 of surface area. PPT measurements using these two instruments differ." The Fischer instrument is convenient in the clinic but is expensive. After a preliminary trial on the forearm and explanation of the method, the amount of pressure required to elicit pain in any specific site is recorded. After application to the skin, the pressure gauge is advanced at the rate of 1 kg of pressure per second. The subject is instructed to indicate when the pressure sensation changes to pain. At that time, the instrument is withdrawn, and the indicator needle stops automatically on the highest amount of pressure applied and stays at that measurement until it is reset. There are high correlations between use of a pressure dolorimeter and use of the thumb," although use of the thumb or finger provides further information about "feel" of the tissue and reaction by the subject that is clinically useful, although difficult to quantitate.

Classification Criteria

PPT is assessed at sites deemed to be tender points and at sites deemed not tender, so-called control points. 108 Both sites have lowered PPT in FMS patients compared to control subjects. 4n In general, PPT of less than 4 kg/cm2, roughly equivalent to the pressure induced by the thumb with the fingernail blanched, i.e. deemed to represent a tender point. A positive rep]y to the question "does this hurt or is it painful?" constitutes a positive response. This yes-no response is more reliable than scoring of degree of tenderness on a O to 4 scale: Tenderness itself is not to be taken as a positive response. The number of tender points can be added. Various classification criteria sets have included the number of tender points to classify an individual as having FMS.10 The ACR 1990 classification criteria for FMS include the need for widespread pain (upper and lower body and bilateral), together with ll of a possible 18 predesignated points being deemed as tender points.108 These criteria have a high specificity and sensitivity with an accuracy of 84.9%,, higher than most other criteria sets. The methodology in constructing such criteria has been criticized, 75 but it is now widely used and appears to identify a uniform patient population. Although validated in the clinic, ACR criteria have been used in community surveys.

The Muller criteria 76 identify somewhat more individuals as having FMS, whereas the Yunus criteria, "2 when used correctly, appear to give similar results to the ACR criteria. There are no direct comparative studies, however. The ACR criteria depend on palpation to identify tender points, but many other studies use dolorimeter criteria. It has been suggested that the dolorimeter may be a less reliable and valid method for identifying tender points. 76

Regional pain complaints without identifiable cause and with accompanying clinical features typical of (generalized) FMS are common and the nomenclature localized fibromyalgia is used by many clinicians. No satisfactory classification criteria exist for such syndromes, but regional tender point counts together with regional pain complaint and other features characteristic of FMS appear to be a useful operational compromise. "~ " In such situations, care is needed to exclude a nociceptive cause of the regionalized pain, such as a trigger point or deeply located paraspinal tissue pathology. Classification criteria are not synonymous with diagnostic criteria, in which the global picture is taken into account. Although the ACR criteria appear to be useful for diagnosis in the clinic, FMS presents as a spectrum of clinical features and fluctuates with time. The diagnostic process includes all dimensions of FMS, not just the widespread pain and hyperalgesia of the ACR classification criteria.

Myalgic scores

Various combinations of PPT may be used to construct a myalgic score (Table 2). Using digital palpation, a rating for elicited pain can be given as follows: O = no pain, 1 = mild pain, 2 = a verbal exclamation of pain, and 3 = withdrawal or flinching. In such a scale, the ACR designated tender point sites are evaluated, and the maximum score thus is 54 (i.e., 3 x 18)." PPT in kg/cm2 may be measured directly and adduced across all or selected tender and/or control points. No uniform system exists to describe this, but a total myalgic score using Dolorimetry appears helpful and is useful as a comparison between groups. To accommodate for localized fibromyalgia, a scoring system using selected ACR tender points plus control points can be used. In this system, an algometer can record PPT, which can be scored as follows: O = >4 kg/cm2, 1= >3, 2 = >2, 3 = <2. These can be added across all 18 standard ACIi tender point sites, and control points, or representative sites from each quarter of the body also can be used. 44, 46

Other PPT measures

PPT also can be assessed using other noxious modalities such as thermal or chemical stimuli.41, 61. There is a need for further refinement in regard to choice and use of instrument to measure PPT,104 the establishment of normal ranges, changes with age, sex, and ethnic and cultural background factors, as well as the distribution of changes in PPT over the body surface in healthy people.

Allodynia

Allodynia also reflects a reduction in pain threshold. This sign is usually elicited by palpation of a fold of skin gently pinched between the thumb and forefinger and rolled over an area such as the upper back. Allodynia can be scored as being present or absent, and the amount of discomfort present may be rated on a Ritchie-like scale of O= no pain, 1 = mild pain (painful test with mild discomfort only), 2 = moderate pain (painful test with obvious discomfort but without Pain Tolerance.

Pain tolerance is the level at which a person refuses to accept any further increase in noxious stimulation. This variable is dependent on a variety of social, cultural, and psychologic factors. Pain tolerance may be evaluated using the mechanical stimulus of a pressure algometer. This instrument may need a larger scale than that used to measure pressure pain threshold (O to 13 kg/cm2 compared to O to ll kg/cm2 on a more standard instrument). To measure pain tolerance, the instrument continues to be applied at 1 kg per second increase in pressure until the subject indicates they cannot accept any further pain by stating the word "stop".73. Many people with FMS have lowered pain tolerance .withdrawal reaction), 3 = severe pain (painful test with withdrawal reaction). The highest intensity of pain is chosen from all regions tested.46

Table 2. MYALGIC SCORES IN FMS


Right Left

TeP PPT TeP PPT

Examination Point (0-3) (kg/cm') (0-3) (kg/cm')

ACR Points

  1. Occiput [at suboccipital muscle insertion]
  2. Low cervical [anterior aspect of intertransverse spaces CS-C7]
  3. Trapezius [midpoint upper border]
  4. Supraspinatus [origin above medial border scapular spine]
  5. Second rib [upper surface just lateral to costochondral junction]
  6. Lateral epicondyle [2 cm distal to epicondyle]
  7. Gluteal [upper outer quadrants of buttocks in anterior fold of muscle]
  8. Greater trochanter [posterior to trochanteric prominence]
  9. Knee [medial fat pad proximal to joint line]
  10. Control Points
    1. Mid deltoid
    2. Thumb
    3. Mid anterior thigh
    4. Big toe

ACR Tender Point Score - number of Tender Points 1-9 right and left-maximum 18.

Total Myalgic Score

  1. qualitative-sum of scores 0-3 (see text) of each Tender Point-maximum 54
  2. quantitative-sum of all PPT values at every Tender Point

Total Control Score-sum of all PPT values at sites 10-13

Regional Tender Point Pressure Threshold Score (accommodates localized FMS)-the lowest PPT at each of four bilateral sites (4,5,8 and 9) modified according to O = > 4 kg/cm2. 1 = 1=> 3, 2 = > 2, 3 =< 2 kg/cm2. Maximum score = 4 x 3 = 12

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