Pain is considered chronic when it is constant or recurrent and lasts for more than 3 months. It may persist because of ongoing tissue inflammation, as seen in children with inflammatory bowel disease or juvenile rheumatoid arthritis.
It may also occur without tissue inflammation when peripheral or central nervous system neurons become abnormally modified by disease or lesion, or neuropathic pain. Neuropathic pain syndromes are an enigmatic and heterogeneous group of disorders that have been recognized by a variety of names for over 100 years and continue to baffle physicians, patients, and their families. This perplexity stems from the lack of known precise pathophysiologic mechanisms responsible for the debilitating symptoms. Neuropathic pain syndromes are likely caused in part by abnormalities of the peripheral, central, and autonomic nervous system. Other contributory factors include myofascial dysfunction and/or psychological distress. Neuropathic pain conditions are best understood through a biopsychosocial framework wherein multiple factors contribute to the manifestation of this complex pain presentation.
Neuropathic pain is not as uncommon during childhood as once thought. The most common type of neuropathic pain in children is complex regional pain syndrome type 1 (CRPS-1), which is the focus of this chapter.
Complex Regional Pain Syndrome
In 1993, the International Association for the Study of Pain (IASP) recommended that neuropathic pain syndromes should be grouped together and called complex regional pain syndrome (CRPS). CRPS is divided into two different types depending on the initiating injury: CRPS type 1 (formerly called reflex sympathetic dystrophy) follows a soft tissue injury, and CRPS type 2 (formerly called causalgia) follows a peripheral nerve injury. CRPS-2 is rare in children and will not be discussed further in this chapter.
The differential diagnosis of a painful condition involving the distal extremity is long (see Table 36.1 ).
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It is usually possible to eliminate most conditions based on the results of prior diagnostic evaluations, history, and physical examination. Furthermore, the diagnosis of CRPS-1 is excluded by the existence of conditions that would otherwise account for the degree of pain and dysfunction. Unfortunately, there are no tests that can confirm the diagnosis of CRPS-1. The IASP has established and validated diagnostic criteria for CRPS-1 called the “Budapest Criteria ” after an international consensus meeting was held there in 2003. However, it still remains a diagnosis of exclusion.
Delayed diagnosis of CRPS-1 is common and may exceed a year from the time symptoms begin. Diagnostic delays lead to prolonged pain, suffering, and disability, and may result in harmful therapies such as splinting or casting. Immobilization of the effected extremity may exacerbate the condition.
There are several aspects of CRPS-1 in children that may provide clues to the proper diagnosis. As with adults, females are affected more than males by a ratio of 4:1, but unlike adults, the lower extremities are most often affected. A history of trauma, albeit trivial, can be elicited in many children. Frequently the trauma occurs during an organized sporting event. At the time of diagnosis, many of these children are disabled and unable to attend school or participate in normal activities. Some children with lower-extremity CRPS-1 are able to ambulate with crutches, but in more extreme cases children are bedridden or wheelchair bound.
Children diagnosed with CRPS-1 will often manifest psychological symptoms that contribute to their pain and disability. These include fear, anxiety, anger, depression, maladaptive coping skills and behaviors, and sleep disturbances. In three large pediatric reports, psychological disorders were identified in 25% to 77% of patients.
Clinical Signs and Diagnosis
The clinical presentation of children with CRPS is heterogeneous and starts with pain that can be out of proportion to any inciting event, which in many instances is minor or even absent. The individual should report change in the following four categories: sensory, vasomotor, sudomotor, and motor changes. They should also report these changes during examination. Per the Budapest Criteria, the individual should report a constellation of at least one symptom from three of the four categories and the physician should document at least one sign in two or more categories during the physical exam. Lastly, as CRPS remains a diagnosis of exclusion, no other disease process should better explain all the signs and symptoms of the child.
The sensory symptoms of allodynia (defined as pain caused by a stimulus that does not normally provoke pain) or hyperesthesia (defined as increased sensitivity to stimulation) are usually the most obvious cues to the child that something is amiss. A wool sock might be so scratchy that the child must remove it immediately, or the pressure of a bed sheet on the affected extremity causes extreme pain. Often, these unusual sensations cause the child to sleep with an extremity propped in the air so that nothing touches or stimulates the affected extremity. Hygiene can become difficult if the temperature of warm water used in bathing is felt as scalding water on the child’s affected body part. These sensory changes are not often in a dermatomal distribution and can be described as “burning, sharp, or achy.” On examination, pinprick may provoke hyperalgesia while vibration or light touch or joint movement may provoke allodynia.
The vasomotor changes relate to color or temperature changes in the skin. This can be asymmetric color or temperature changes between the affected and unaffected extremity or skin color changes over the affected body part. An adolescent may mention or display periods of redness and warmth followed by other periods of mottled or pale skin. Infrared thermometry can confirm temperature differences which in some studies vary by 0.6°C between the colder affected limb and the unaffected limb.
The sudomotor changes described by the child may consist of edema or sweating. Often these reports will consist of asymmetric changes that have no apparent provocation. The affected limb will have edema or unusual sweating. A swollen, discolored extremity has been the classic presentation of CRPS. Direct examination and comparison with the unaffected limb can yield signs of sudomotor changes.
Finally, motor and trophic changes can have the most significant effect on the functional ability of the adolescent. There could be complaints of hair loss over a distal extremity or brittle nails. Other trophic changes can involve the bones losing density and wasting of the skin, tissue, and muscle. The adolescent may complain that she is unable to complete simple tasks because of weakness or that tremors affect her handwriting. Problems using the affected area often limit participation in activities such as sports, dance, music playing, and social events. Often, routine activity such as school attendance is abandoned because of the functional disability associated with CRPS.
Therapies
Reported therapies include nonsteroidal antiinflammatory drugs (NSAIDs), tricyclic antidepressants, opioids, anticonvulsants, corticosteroids, sympathetic blocks, physiotherapy, transcutaneous electrical nerve stimulation (TENS), and psychological therapies, particularly cognitive-behavioral therapies. Although most of these achieve modest success, none has proven effective in prospective, controlled, clinical trials. Yet children with CRPS-1 appear to be more responsive to therapy than adults. Combinations of the above therapies result in resolution of symptoms in 46% to 69% of children, the average recovery time being 7 weeks (range 1 to 140 weeks). In recent years, several intensive interdisciplinary pain rehabilitation programs using inpatient and day-hospital models have demonstrated large improvements in functioning and reductions of pain in children treated with a combination of intensive physical therapy, occupational therapy, and cognitive-behavioral therapies, with or without medications or sympathetic blocks.
Children with CRPS are best cared for by an experienced multidisciplinary team of individuals that includes a physician, a psychologist, and a physical therapist. The physician confirms the diagnosis, coordinates physical and psychological therapies, and when appropriate starts medications or performs sympathetic blocks to facilitate participation in physical therapy.
Daily physical therapy is the cornerstone of treatment for children with CRPS-1. It should focus on desensitization, full weight-bearing, and functional usage of the extremity. The goal is to return the affected extremity to normal functioning, rather than only pain relief. The therapist should acknowledge the presence of pain during initial treatments but continue nonetheless. It is thought that the pain of CRPS-1 results when the body misinterprets sensory information and responds as though an acute injury is in progress. Physical therapy halts this inappropriate response and reestablishes normal neuronal responses. The central nervous system is bombarded with “normal” sensory information such as the perception of touching or weight-bearing by using the affected body part in functional activities.
Additional therapies such as hot and cold packs, TENS, and ultrasound are not usually effective. Immobilization of the affected limb is contraindicated because it may enhance progression of the disease.
Psychological Assessment
The purpose of psychological assessment is to estimate the severity of the child’s and the family’s pain-related distress and dysfunction and to assist in treatment planning. The psychologist will attempt to gain an understanding of their expectations for treatment, their coping styles and skills, recent stressful events and other life changes, and developmental and social histories. The psychologist will help the child and family understand the mechanism of the pain in general terms and will teach coping strategies, relaxation techniques, techniques that maximize function, and cognitive restructuring techniques to address negative thinking. The psychologist will evaluate symptoms of depression and anxiety and will teach the child and family how to increase their sense of self-control over the pain and disability.
Some families may resist psychological involvement because they view it as an indication that the pain is psychosomatic. Therefore the medical team should present psychological therapy as an integral component of the global pain management program and inform families of the ways in which psychological techniques are useful in pain management. The treatment team should emphasize the mind-body connection so that patients understand that pain is not necessarily a medical or psychological entity, but rather that pain treatment requires a combination of medical and psychological approaches.
There is a growing consensus in chronic pain research that the immune system is clinically involved in the mechanistic changes that occur between acute and chronic pain. Through the communication between neurons and immune cells, the immune system has the ability to propagate and maintain a chronic pain state including neuropathic pain such as CRPS. The immune system can work both peripherally and centrally to release mediators that sensitize neurons which provide a positive feedback loop which can perpetuate chronic pain. This might in part explain why many current medications are poor at treating chronic pain as almost none slow this immune-mediated-positive feedback loop while multidisciplinary programs have some success by focusing on improved function and exercise, regulated sleep, improved diet, and psychological stress reduction, which are all demonstrated to improve immune system function.
Clinical Course and Progression
The clinical course and progression of CRPS-1 is highly variable and difficult to predict with reasonable accuracy. Most children will experience a remission of symptoms but about 30% will relapse at the original site or at a new location. Outcomes are variable, with some children returning to their premorbid activities and others having a chronic, progressive course with severe pain and disability.
In summary, CRPS-1 is a chronic pain disorder associated with significant morbidity. Its inciting factors and pathophysiology are not fully known. Prompt intervention by an experienced multidisciplinary team can lead to resolution of severe symptoms in most children. However, remissions marked by persistent pain and disabilities are common.
References
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