All chronic musculoskeletal pain syndromes involve pain complaints of at least 3 mo in duration in the absence of objective abnormalities on physical examination and laboratory screening. Additionally, children and adolescents with musculoskeletal pain syndromes often complain of persistent pain despite previous treatment with nonsteroidal anti-inflammatory drugs and analgesic agents. The location varies, with pain complaints either localized to a single extremity or more diffuse and involving multiple extremities. The prevalence of musculoskeletal pain syndromes increases with age and is higher in females, thus rendering adolescent girls at highest risk.

The pain complaints of children and adolescents with musculoskeletal pain syndromes are commonly accompanied by psychologic distress, sleep difficulties, and functional impairment throughout home, school, and peer domains. Psychologic distress can include symptoms of anxiety and depression, such as frequent crying spells, fatigue, sleep disturbance, feelings of worthlessness, poor concentration, and frequent worry. Indeed, a substantial number of children with musculoskeletal pain syndromes display the full range of psychologic symptoms, warranting an additional diagnosis of a comorbid mood or anxiety disorder (e.g., major depressive episode, generalized anxiety disorder). Sleep disturbance in children with musculoskeletal pain syndromes may include difficulty falling asleep, multiple night awakenings, disrupted sleep-wake cycles with increased daytime sleeping, nonrestorative sleep, and fatigue.

For children and adolescents with musculoskeletal pain syndromes, the constellation of pain, psychologic distress, and sleep disturbance often leads to a high degree of functional impairment. Poor school attendance is common, and children may struggle to complete other daily activities relating to self-care and participation in household chores. Peer relationships may also be disrupted because of decreased opportunities for social interaction due to pain. Therefore, children and adolescents with musculoskeletal pain syndromes often report loneliness and social isolation, characterized by having few friends and lack of participation in extracurricular activities.

Adapted from Anthony KK, Schanberg LE: Assessment and management of pain syndromes and arthritis pain in children and adolescents, Rheum Dis Clin N Am 33:625–660, 2007.

Juvenile primary fibromyalgia syndrome (JPFS) is a common pediatric musculoskeletal pain syndrome. Approximately 25-40% of children with chronic pain syndromes can be diagnosed with JPFS. Although specific diagnostic criteria for JPFS have not been determined, all children and adolescents with JPFS have diffuse musculoskeletal pain in at least 3 areas of the body that persists for at least 3 mo in the absence of an underlying condition. Results of laboratory tests are normal, and physical examination reveals at least 5 well-defined tender points (Fig. 162-1). Children and adolescents with JPFS also present with many associated symptoms, including nonrestorative sleep, fatigue, chronic anxiety or tension, chronic headaches, subjective soft tissue swelling, and pain modulated by physical activity, weather, and anxiety or stress. There is considerable overlap among the symptoms associated with JPFS and the complaints associated with other functional disorders (e.g., irritable bowel disease, migraines, temporomandibular joint disorder, premenstrual syndrome, mood and anxiety disorders, and chronic fatigue syndrome), raising speculation that these disorders may be part of a larger spectrum of related syndromes.

Figure 162-1 Fibromyalgia tender points.

Although the precise cause of JPFS is unknown, there is an emerging understanding that the development and maintenance of JPFS are related both to biologic and psychologic factors. JPFS is an abnormality of pain processing characterized by disordered sleep physiology, enhanced pain perception with abnormal levels of substance P in cerebrospinal fluid, disordered mood, and dysregulation of hypothalamic-pituitary-adrenal and other neuroendocrine axes resulting in lower tender point pain thresholds and increased pain sensitivity. Children and adolescents with fibromyalgia also often find themselves in a vicious cycle of pain, whereby symptoms build on one another and contribute to the onset and maintenance of new symptoms (Fig. 162-2).

Figure 162-2 Cycle promoting juvenile primary fibromyalgia syndrome symptoms and their maintenance.

(Adapted from Anthony KK, Schanberg LE: Juvenile primary fibromyalgia syndrome, Curr Rheumatol Rep 3:162–171, 2001.)

JPFS has a chronic course that can detrimentally affect child health and development. Adolescents with JPFS who do not receive treatment or are inadequately treated may withdraw from school and the social milieu, complicating their transition to adulthood. Treatment of JPFS generally follows consensus statements of the American Pain Society. The major goals are to restore function and to alleviate pain, and treatment should address co-morbid mood and sleep disorders. Treatment strategies include parent/child education, pharmacologic interventions, exercise-based interventions, and psychologic interventions. Graduated aerobic exercise is the recommended exercise-based intervention, whereas psychologic interventions should include training in pain coping skills, stress management skills, and sleep hygiene. Drug therapies, although partially unsuccessful in isolation, may include tricyclic antidepressants (amitriptyline 10-50 mg orally 30 minutes before bedtime), selective serotonin reuptake inhibitors (sertraline 10-20 mg daily), and anticonvulsants. Pregabalin was approved by the U.S. Food and Drug Administration (FDA) for treatment of fibromyalgia in adults but has not yet been studied in children. Muscle relaxants are generally not used in children, because they often adversely affect school performance.

Complex regional pain syndrome (CRPS) is characterized by ongoing burning limb pain that is subsequent to an injury, immobilization, or another noxious event affecting the extremity. CRPS1, formerly called reflex sympathetic dystrophy, has no evidence of nerve injury, whereas CRPS2, formerly called causalgia, follows a prior nerve injury. Key associated features are pain disproportionate to the inciting event, persisting allodynia (a heightened pain response to normally non-noxious stimuli), hyperalgesia (exaggerated pain reactivity to noxious stimuli), swelling of distal extremities, and indicators of autonomic dysfunction (i.e., cyanosis, mottling, and hyperhidrosis) (Table 162-4).

Table 162-4 DIAGNOSTIC CRITERIA FOR COMPLEX REGIONAL PAIN SYNDROME

Data from Wilder RT, Berde CB, Wolohan, M, et al: Reflex sympathetic dystrophy in children: clinical characteristics and follow-up of seventy patients, J Bone Joint Surg Am 74:910–919, 1992.

The diagnosis requires the following: an initiating noxious event or immobilization; continued pain, allodynia, hyperalgesia out of proportion to the inciting event; evidence of edema, skin blood flow abnormalities, or sudomotor activity; and exclusion of other disorders. Associated features include atrophy of hair or nails; altered hair growth; loss of joint mobility; weakness, tremor, dystonia; and sympathetically maintained pain.

Although the majority of pediatric patients with CRPS present with a history of immobilization or minor trauma or repeated stress injury (e.g., caused by competitive sports), a sizeable proportion are unable to identify a precipitating event. Usual age of onset is between 9 and 15 yr, and girls with the disease outnumber boys with the disease by as much as 6 : 1. Childhood CRPS differs from the adult form in that lower extremities rather than upper extremities are most commonly affected. The incidence of CRPS in children is unknown, largely because it is often undiagnosed or diagnosed late, with the diagnosis frequently delayed by nearly a year. Left untreated, CRPS can have severe consequences for children, including bone demineralization, muscle wasting, and joint contractures.

The treatment of CRPS involves a multistage treatment approach. Aggressive physical therapy should be initiated as soon as the diagnosis is made, and cognitive-behavioral therapy (CBT) should be added as needed. Physical therapy is recommended 3 or 4 times/wk, and children may need analgesic premedication at the onset. Physical therapy is initially limited to desensitization and then moves to weight-bearing, range-of-motion, and other functional activities. CBT used as an adjunctive therapy targets psychosocial obstacles to fully participating in physical therapy and provides pain coping skills training. Sympathetic and epidural nerve blocks should be attempted only in refractory cases and only under the auspices of a pediatric pain specialist. The intent of both pharmacologic and adjunctive treatments for CRPS is to provide sufficient pain relief to allow the child to participate in aggressive physical rehabilitation. If CRPS is identified and treated early, the majority of children and adolescents with the disease can be treated successfully with low-dose amitriptyline (10-50 mg orally 30 minutes prior to bedtime), aggressive physical therapy, and CBT. Opioids and anticonvulsants such as gabapentin can also be helpful. Notably, multiple studies have shown that noninvasive treatments, particularly physical therapy and CBT, are at least as efficacious as nerve blocks in children with CRPS.

Children with erythromelalgia experience episodes of intense pain, erythema, and heat in their hands and feet (Fig. 162-3) and less commonly in their face, ears, or knees. Symptoms may be triggered by exercise and exposure to heat, and they last for hours and occasionally for days. Although most cases are sporadic, an autosomal dominant hereditary form results from a mutation in the gene SCN9A on chromosome 2q31-32, which is responsible for sodium channel function in dorsal root ganglia. Erythromelalgia is also associated with an array of disorders, including myeloproliferative diseases, peripheral neuropathy, frostbite, hypertension, and rheumatic disease. Treatment includes avoidance of heat exposure as well as other precipitating situations and the utilization of cooling techniques that do not cause tissue damage during attacks. Nonsteroidal anti-inflammatory drugs, narcotics, anesthetic agents, anticonvulsants, and antidepressants as well as biofeedback and hypnosis may be useful in managing pain. Drugs acting on the vascular system (aspirin, sodium nitroprusside, magnesium, misoprostol) may also be effective.

Figure 162-3 Typical redness and edema of the foot in erythromelalgia.

(From Pfund Z, Stankovics J, Decsi T, et al: Childhood steroid-responsive acute erythromelalgia with axonal neuropathy of large myelinated fibers: a dysimmune neuropathy? Neuromusc Disord 19:49–52, 2009.)