A prospective study assessing the prevalence and etiology of pain in children and young adults with cancer treated by the pediatric branch of the National Cancer Institute over a 6-month period demonstrated that pain was present in 54% of hospitalized patients and 25% of outpatients. The individual frequencies of the various causes of pain differed markedly from those reported in a similar adult series. Tumor-related pain accounted for 34% of the pain experienced by hospitalized children and only
18% of the pain experienced by outpatients. Treatment-related pain was commonly reported in children who were both inpatients and outpatients. Even in patients with active malignancy, tumor-associated pain accounted for only 46% of the pain experienced, and therapy-related pain accounted for 39%; pain of both etiologies was reported by 14% of patients.

Several obvious differences between adult and pediatric malignancies contribute to these reported differences. First, the spectrum of malignancies seen in children is different from that in adults. The most common malignancies seen in children (acute lymphoblastic leukemia, primary brain tumors, rhabdomyosarcoma, neuroblastoma, and other soft tissue and bone sarcomas) are rarely seen in adults, whereas carcinoma, the most common adult malignancy, rarely occurs in children. Second, most pediatric malignancies become widely metastatic and are rapidly fatal once they become refractory to standard therapy. An adult, by contrast, may survive for many years with advanced disease. Third, most pediatric cancers are initially managed with aggressive multimodal treatment regimens that combine surgery, radiation therapy, and chemotherapy. These treatments are highly effective in inducing tumor remission but also result in considerable morbidity. Fourth, when conventional therapy is no longer effective, many children continue to receive anticancer treatment (often investigational treatment) until shortly before their death. This approach is designed to test new treatment strategies and to offer an approach that reasonably addresses parental concerns; however, it inevitably leads to an increase in treatment-related morbidity and pain for children.

In other chronic and terminal illnesses in children, such as AIDS, cystic fibrosis, and congenital heart disease, pediatric patients may have the more “adult” experience of prolonged disability with superimposed acute exacerbations and intervention-related distress.

Until recently, many clinicians assumed that “neurologic immaturity” prevents very young children from experiencing pain. Current research disputes this contention. Pain transmission pathways develop during fetal life. Nerve tracts in the spinal cord and brainstem begin to myelinate around the gestational age of 22 weeks and are completely myelinated by 28 to 30 months after birth. More specifically, myelination is complete up to the thalamus by 30 weeks’ gestation, and the thalamocortical pain connections to the cortex are myelinated by 37 weeks’ gestation. Therefore, pathways that conduct noxious information from nociceptor to cortex are present in the newborn infant. Cortical descending inhibition develops postterm.

Most neurotransmitters and neuromodulators are present in the fetus. Calcitonin gene-related peptide (CGRP) and substance P are present at 8 to 10 weeks’ gestation, whereas others such as enkephalin and vasoactive intestinal peptide (VIP) appear 2 to 4 weeks later. Catecholamines are present in late gestation, and, in
the human fetus, serotonin has been found at 6 weeks postnatally. Neurotransmitters that enhance the perception of pain are produced earlier in the fetus than are endogenous opioids.

It appears, therefore, that pain processing in the mature fetus and newborn is adequately developed so that the infant may exhibit behavioral and physiologic responses to noxious stimuli and may even have enhanced nociception. The misconception that neonates and infants do not feel pain combined with a fear of using opioids in very young children resulted in gross undertreatment of pain in this population. Recent research has emphasized the importance of providing adequate pain control in newborns and young infants. It is now clear that the undertreatment of pain can have major short-term physiologic effects. The long-term consequences of untreated pain in the developing organism are not yet defined, but some studies suggest that early pain responses influence later pain behaviors.

Piagetian theory is often used to describe the developmental levels of understanding pain in school-age children; these levels are listed in Table 1. Speculations about younger children have been extrapolated from that framework. However, recent findings have shown that younger children have a more sophisticated understanding of pain than was previously reported. Children of 18 months of age can express and localize pain. Although younger children may recover more rapidly from surgery and report less pain after surgery, they typically have more pain from needle procedures that older children. Young children’s limited cognitive development may preclude an understanding of the context of the needle pain, the realization that the pain will be over quickly, and the use of effective cognitive coping strategies.

Coping strategies are influenced by cognitive development. Children as young as 18 months indicate, through structured play sessions, the awareness of ways to eliminate their pain, generally by seeking hugs and kisses and asking for medicine. Children who
are 3 to 4 years of age spontaneously use distraction and also report that play makes them feel better. Although they may use this technique spontaneously, children cannot deliberately distract themselves or use self-initiated cognitive strategies to decrease pain before the age of approximately 5 years. Cognitive and behavioral strategies, such as relaxation, are generally beyond their capabilities.

Communicating pain is also influenced by cognitive development (see section entitled General Principles in subsequent text).

The assessment of pain in children should be systematic, and requires reevaluation throughout the course of the illness. Because infants cannot communicate verbally, behavioral and physiologic responses can be used to assess pain in the very young, including facial expression, tachycardia, and stress-related hormones. However, these signs may not be specific to pain. The child’s cognitive development and ability to understand pain influence the choice of suitable measurement tools.

In children, pain measurement must consider the following:

Measurement tools are summarized in Table 2.

Children as young as 18 months can indicate their pain and give a location, but it is not possible to obtain a self-report of intensity of pain before approximately 3 years of age. Children who are 3 years old can give a gross indication, such as “no pain,” “a little pain,” and “a lot of pain.” Similarly, many children at this age can use concrete measures such as “poker chips” representing “pieces of hurt” to convey the intensity of their pain. The use of more abstract self-report instruments, such as the “smiling faces scale” (see Chapter 6

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