Chronic Overlapping Pain Conditions

Prevalence

The prevalence of COPCs is unknown, ranging from 20% to >50% depending on which symptom is being assessed and how much overlap exists across disorders. A large study from 28 countries (about 400,000 participants) found a prevalence of headache of 54%, stomachache 50%, and backache 37%, occurring at least once a month for at least 6 mo. Females had a higher prevalence of having all 3 complaints when compared to males; the prevalence increased with age. These three pain syndromes, headache, stomach-ache and backache, frequently coexist.

IBS and chronic abdominal pain affect 6–20% of children and adolescents. Idiopathic musculoskeletal pain affects about 16% of schoolchildren age 5-16 yr and is often associated with sleep disturbances, headache, abdominal pain, daytime tiredness, and feeling sad (see Chapter 193 ). Migraines present >6 mo occur in about 8% of the population (children and adolescents <20 yr) (see Chapter 613.1 ). Fibromyalgia is present in 1.2–6% (see Chapter 193.3 ). The prevalence of chronic disabling fatigue increases during adolescence from about 1.9% at age 13 to 3% at 18 yr (see Chapter 147.1 ). As with most COPCs, fibromyalgia has many comorbid disorders, such as sleep disturbance, fatigue, headache, sore throat, joint pain, and abdominal pain. The American College of Rheumatology definition of fibromyalgia incorporates some of these comorbid conditions.

Symptom/Disorder Overlap

Diagnostic criteria of many of these disorders overlap with one another, making differentiation between two disorders more of a semantic issue rather than a clinical differentiation. Chronic fatigue syndrome (CFS) , clinically the most concerning symptom, shares many of the diagnostic criteria with fibromyalgia. Patients with a single pain condition, such as fibromyalgia, CFS, IBS, multiple chemical sensitivity (MCS), headaches, or temporomandibular joint disorder (TMJD), will typically have another disorder. This overlap of symptoms may reflect a shared pathophysiology, possibly a central nervous system (CNS) dysfunction, as was implied in the prior term “central sensitization syndrome”. A CNS pathophysiology would also explain the “invisibility” of these disorders to usual screening tools that most often target an end organ.

COPCs also harbor many symptoms that are not strictly “pain,” although they may be equally or more disabling. Adolescents seen in a tertiary referral center with a functional gastrointestinal disorder (FGID) also manifest dizziness, chronic nausea, chronic fatigue and sleep disturbance, as well as migraines. Up to 50% of adolescents complain of weekly fatigue, and 15%, daily fatigue.

Migraine headaches are frequently associated with anxiety and depression. Anxiety also predicts the persistence of migraine headaches. Sleep disturbance and migraine also interact closely. Poor sleep can trigger a migraine or a migraine cluster; migraine headache itself disturbs sleep. Juvenile fibromyalgia is associated with sleep disturbances such as prolonged sleep latency, frequent awakening, less total sleep time, and periodic limb movements. Adult patients with IBS also have sleep disturbances, correlating with anxiety, depression, and stress.

The comorbidities of hypermobility Ehlers-Danlos ( hEDS ) and postural orthostatic tachycardia syndrome (POTS) have been significant. Patients with hEDS may complain of widespread and sometimes debilitating pain with or after activity, severe fatigue, handwriting difficulties, “cracking” of joints, joint swelling, joint dislocation, subluxation, or back pain. The chronic pain reduces exercise tolerance, with poorer quality of life and an ever-worsening cycle because exercise is a key piece of management. Patients with FGID may also have hEDS, fibromyalgia, chronic pains, and higher somatizations scores than those with organic gastrointestinal (GI) disorders.

Diagnosis of pediatric POTS requires an increase in heart rate >40 beats/min in the 1st 10 min of upright tilt test associated with orthostatic symptoms. POTS is also associated with multiple comorbidities, including sleep disruption, chronic pain, Raynaud-like symptoms, GI abnormalities, and less frequently headaches, syncope, and urinary complaints. Patients with both POTS and hEDS usually have more migraines and syncope than those with POTS alone. The prevalence of comorbid disorders in children with COPC is identical whether they have POTS or hEDS.

Psychiatric Comorbidities

Many of these disorders have significant psychiatric comorbidities. Juvenile fibromyalgia is associated with anxiety disorders and major mood disorders. Children with medically unexplained symptoms generally have more anxiety and depression than children with other chronic disorders. Other associations include disruptive behaviors, symptom internalization, fearfulness, greater dependency, hyperactivity, and concern about sickness.

Predisposing Factors

Female gender and older age (adolescence) increase the risk of COPCs. Certain conditions (e.g., headache) are more common in males or have similar prevalence across genders during childhood, but the prevalence in females increases after puberty. Trauma or posttraumatic stress disorder increases psychological comorbidities in juvenile fibromyalgia. Some studies suggest that anxiety predisposes to chronic pain. A population-based study following children from 18 mo to 14 yr of age suggested that maternal psychological distress in early childhood and depressive and pain complaints in preadolescence increase the risk of recurrent abdominal pain at age 14. Postinfectious IBS is an identifiable risk factor for new-onset anxiety, depression, and sleep disruption in adults. Children with recurrent abdominal pain often have parents with abdominal pain. It is unclear if this association is caused by a common environmental/genetic factor or a learned behavior of the child imitating the parent.

Natural History

The natural history of COPC is not well known. Chronic disabling fatigue in the general adolescent population persists 2-3 yr in about 25% of patients, but only 8% of youth affected at age 13 still had the complaints at ages 16 and 18. A meta-analysis suggests that the prognosis of CFS in children is usually good, with a small minority having persistent disabling symptoms. The patient's belief in an underlying physical disorder and the presence of psychiatric comorbidities predicts a poorer outcome.

In a study of children with FGID, the outcome depended on specific variables. Those who perceived their abdominal pain as more threatening, with high levels of pain catastrophization and little capacity to cope with pain because of reduced activity levels, had a poorer outcome. This “high pain dysfunctional profile” subgroup was predominantly female (70%) with a mean age of 12.2 yr. Two thirds of this subgroup still complained of FGID at follow-up, vs about one third of those in the other groups. These groups included a “high pain adaptive profile” group with similar pain levels but better adaptive skills and less catastrophization, predominantly slightly younger (11.8 yr) females, and a “low pain adaptive profile” group, slightly younger (11.1 yr), with equal males and females but less abdominal pain, better coping mechanisms, and less impairment of daily activities. In the high pain dysfunctional profile group, 41% had both FGID and nonabdominal chronic pain at follow-up, vs 11% in the high pain adaptive and 17% in the low pain adaptive group. Another study following children age 4-16.6 yr with IBS demonstrated resolution of symptoms in 58%, usually without medication. The differences between these studies may result from the age of the groups, with better outcome in the younger patients, as well as the number of comorbidities and psychological profile.