Pain Amplification Syndromes

Evaluation of Musculoskeletal Pain

Pain is the subjective expression of an unpleasant sensation or emotional experience associated with actual or perceived tissue damage. It is difficult, if not impossible, for an observer to know with any certainty to what extent another person is in pain. Even experienced observers may differ in their assessments of the degree of pain a child is experiencing. Although parents and children tend to make a similar assessment of the degree of pain, parents may over- or underestimate their child’s pain in relation to the child’s own self-report. An important premise in the evaluation and management of a child in pain is that the child’s report of pain and its severity must be accepted at face value. According to Meinhart and McCaffery, “Pain is what the patient says it is, and exists when he says it does.” Prolonged malingering in childhood is exceedingly rare and, if present, is best addressed through psychotherapy. For pain management to be effective, the child must know that he or she is believed.

Many interacting issues determine whether a child’s pain disturbs the child’s and the family’s functioning, and when, if ever, medical help should be sought ( Fig. 53.1 ).

Laboratory Examination

It is important to have a clear rationale for undertaking any investigation because these children are at risk for overmedicalization. In many situations, no testing is required. A large number of investigations increase the likelihood of false-positive results that may obfuscate the physician and family, cause unnecessary angst, lead to further testing, and delay appropriate treatment. Usually it is appropriate to evaluate indices of inflammation (i.e., complete blood count, erythrocyte sedimentation rate, and C-reactive protein). It is unwise to make a diagnosis of a noninflammatory condition in a child with an abnormal blood count, or increased acute phase reactants, unless the abnormalities can be clearly ascribed to an intercurrent illness. In the absence of clinical evidence of inflammatory disease, the benefit of obtaining tests for antinuclear antibodies and rheumatoid factor is outweighed by the risk of obtaining false positive results. Imaging studies should be directed to rule in or out a specific diagnosis (e.g., plain radiographs or bone scintigraphy to exclude trauma or tumor and magnetic resonance imaging [MRI] to exclude spinal cord lesions). Bone scintigraphy in adults with complex regional pain syndrome (CRPS) had a sensitivity of only 0.80 and specificity of 0.73. Bone edema is frequently seen on MRI but cannot be differentiated from trauma. There are no data on children and adolescents.

Amplified Musculoskeletal Pain

Many children with severe musculoskeletal pain do not have an identified inflammatory disease or mechanical derangement to cause the degree of pain and associated debility. These children have usually been seen by multiple health care providers, have undergone multiple investigations, and failed multiple therapeutic trials before the correct diagnosis is made. Unfortunately, attempts to identify an increasingly rare and unlikely cause for the pain or escalating empiric treatment aimed at organic pain can result in perpetuating the amplified pain. Kaufman et al. have documented the increasing overmedicalization of children with amplified pain. A physician who recognizes the condition promptly can provide a great service to the child and family by halting further medical investigations and initiating appropriate therapy.

Historical Review

Chronic musculoskeletal pain in children received scant attention until the latter half of the 20th century. In 1951 Naish and Apley published their landmark study on pediatric limb pains resulting from nonarthritic causes. They attributed roles for emotional factors in many of these children. Since then it has been increasingly recognized that a significant number of children suffer from both chronic and amplified musculoskeletal pain. ^, Reflex sympathetic dystrophy (Chronic regional Pain syndrome, CRPS) was first described in a child in 1971. The first description of childhood fibromyalgia was published in 1985. CRPS and fibromyalgia are the subjects of most studies, whereas other, less clearly classified amplified musculoskeletal pain conditions, are less frequently reported.

Definition and Classification

Current terms used to describe these conditions have, until recently, been inadequate and confusing because many children have features that are shared among different subsets. ^, Authors have categorized these children depending on physical features (i.e., the presence of overt autonomic signs or number of painful points with a variety of systemic symptoms) location (localized in one or two body regions), or diffuse (in three or more body regions). ^{, , ,} The new ICD 11 classification defines chronic pain as persistent or recurrent pain for at least 3 months. This minimum duration is arbitrary, but consistent with previous definitions. The main categories are chronic primary pain and chronic secondary pain. Chronic primary pain is a concept originating from the idea that conditions associated with chronic pain should be acknowledged in their own right, even if a clear understanding of the underlying etiology or pathophysiology is missing. From a pediatric musculoskeletal pain perspective, the relevant sections within Chronic Primary Pain are chronic primary musculoskeletal pain and complex regional pain syndrome. Persistent pain in conjunction with a rheumatologic disease (e.g. juvenile idiopathic arthritis) would fall into the Chronic Secondary Pain category, according to this proposal. ^18a The terminology used is, in one sense, moot because evaluation and treatment are similar between subsets. ^{, ,}

In this chapter, the term amplified musculoskeletal pain is used because it is descriptive, does not presume an etiology, and differentiates these children from adults with chronic pain. The word amplified refers to the idea that the body amplifies the pain in much the same way as feedback: a vicious cycle between a microphone and a speaker. It is not meant to imply that the child is willfully hyperbolizing. When evaluating any particular study, it is important to know which criteria were used to classify children with various forms of amplified musculoskeletal pain ( Table 53.1 ). Discrete subsets exist in each of the groups. Specifically, children who fulfill criteria for fibromyalgia and chronic widespread pain are included with those with diffuse idiopathic musculoskeletal pain, and those with CRPS are included with those with localized idiopathic musculoskeletal pain. There is a subset of children with intermittent amplified musculoskeletal pain in whom the criterion for duration is not satisfied; they are, nevertheless, included in some reports because of the severity of their pain and marked dysfunction that may recur over years. Because CRPS and fibromyalgia are relatively distinctive and have their own literature, we use these terms when discussing these specific subsets. There are two kinds of CRPS: type I and type II. Type II is similar to the older term causalgia and implies nerve damage. It is exceedingly rare in children, so further all mention of CRPS refers to type I. Many children present with more than one form of amplified pain, such as CRPS of a limb and localized pain to the back or abdomen or even total body pain. Some children meet the definition for both fibromyalgia and CRPS, but actually there is only one underlying condition: amplified pain. Both fibromyalgia and CRPS have overlapping clinical characteristics, demographics, and response to therapy. ^{, ,}

Epidemiology

There are limited data on the prevalence and incidence of musculoskeletal pain in youth and on the prevalence of pain-associated suffering or disability. However, pain is a common experience during childhood. One study showed that 83% of school-aged children had experienced an episode of pain during the preceding 3 months. Pain is a normal sensation but becomes disabling when it persists and is associated with suffering. In this same study, 31% of the children and adolescents stated that pain had been present for over 6 months. Musculoskeletal pain accounted for 64% of all the pains that were reported. Other studies support this finding and that childhood pain persists into adulthood. ^,

The epidemiology of chronic widespread pain (diffuse amplified pain or juvenile fibromyalgia) is difficult to accurately assess. There are no universally agreed diagnostic criteria, although some authors have suggested using the term juvenile fibromyalgia and proposed diagnostic criteria akin to the adult fibromyalgia criteria. The HUNT study showed that 8.5% of a population of 7373 adolescents in Norway fulfilled their criteria for chronic widespread pain; whereas a UK study showed the prevalence of chronic widespread pain in 17-year-olds to be 4.5%. ^, Other authors have reported fibromyalgia and widespread pain to have a frequency in children and adolescents of 2% to 6%.

Hypermobility, as currently defined, is present in 20% of the normal UK adolescent population. There is a relationship between localized pain and significant hypermobility (Beighton score ≥6).

Low back pain is commonly reported. A UK observational cohort study reported the prevalence of low back pain as 16% in 17-year-olds.

The incidence of CRPS in adults is estimated to be 5 to 26 per 100,000. ^, In children, the epidemiology of amplified pain has not been robustly evaluated, but studies have demonstrated that approximately 80% of the cases reported are girls ranging from 8 to 16 years. There tends to be a delay in recognizing the diagnosis. A complicating factor is the lack of clear diagnostic criteria for children.

There are no specific data regarding the other amplified musculoskeletal pain syndromes, but 5% to 8% of new patients presenting to North American pediatric rheumatology centers most likely have a form of amplified musculoskeletal pain. ^, Many pediatric rheumatologists believe they are seeing increasing numbers of children with amplified musculoskeletal pain.

In juvenile idiopathic arthritis (JIA), it is clear that persistent pain is a significant problem for many children after inflammation is in remission. A significant minority progress to develop localized or diffuse musculoskeletal pain that is not directly related to the control of their inflammatory condition.