Fibromyalgia and Coexisting Chronic Pain Syndromes
Fibromyalgia is associated with many somatic symptoms, including fatigue, gastrointestinal complaints, and headaches. Five physical and psychological symptoms, called the SPADE pentad—sleep disturbance, pain, anxiety, depression, and low energy/fatigue—have been especially prominent in subjects with other chronic pain conditions, making the differential diagnosis sometimes difficult. Indeed, there is a significant overlap between fibromyalgia and what have been termed the functional pain disorders: irritable bowel syndrome (IBS), interstitial cystitis/painful bladder syndrome (IC/PBS), vulvodynia, migraine, and temporomandibular joint disorder (TMJD), also termed orofacial pain. These disorders all are now considered on the spectrum of central sensitization syndromes.
The overlap of symptoms among these syndromes was illustrated in a survey of 2,299 people living in northwest England. Of the almost 2,300 participants, 27% (587 people) reported having 1 or more syndrome, including chronic widespread pain (CWP), orofacial pain, IBS, or chronic fatigue. Of the 587 patients, 404 (18%) had 1 syndrome, 134 patients (6%) reported 2 coexisting conditions, 34 patients (2%) reported 3, and 15 patients (1%) had all 4 syndromes (Table 1).
Having 1 central sensitization syndrome places the patient at higher risk of developing another syndrome,including chronic fatigue syndrome (CFS) and chronic headache. The odds ratio for comorbidity of fibromyalgia, chronic headaches, IBS, TMJD, and IC/PBS has varied from 3 to 20 in twin studies and in large population database surveys. In addition, the number of pre-existing functional somatic syndromes was noted to be a strong risk factor for the presence of fibromyalgia, CFS, and IBS.
Making the Diagnosis
The exact label of a central sensitization syndrome may depend on the type of specialist the patient sees rather than on substantial clinical differences between these common disorders.
A Central Sensitization Inventory (CSI) was proposed as a new self-report screening instrument to help identify patients with these overlapping syndromes, including fibromyalgia. In a study evaluating CSI, approximately 75% of the subjects met clinical criteria for 1 or more central sensitization syndromes, and “CSI scores were positively correlated with the number of diagnosed central sensitization syndromes.”
Irritable Bowel Syndrome
IBS has been reported to occur in 7% to 21% of the general population.Part of the reason there is such a wide variation in reported prevalence is the different diagnostic criteria that have been proposed. According to Chey et al, “Factors important to the development of IBS include alterations in the gut microbiome, intestinal permeability, gut immune function, motility, visceral sensation, brain-gut interactions, and psychosocial status.
IBS is subdivided into 3 categories: IBS with diarrhea, IBS with constipation, or mixed IBS. Symptoms of IBS are similar to those of fibromyalgia and the other central sensitization disorders, including heightened pain sensitivity, excess fatigue, and sleep and mood disturbances.
In addition to overlapping symptoms, IBS and fibromyalgia frequently coexist. The prevalence of IBS in patients with fibromyalgia has varied from 30% to 70%, according to a number of studies. In 1 study from Norway, the prevalence of IBS was found to be 8.4%, with women affected more often than men. Patients with IBS are also at higher risk of having fibromyalgia (OR = 3.6), as well as patients with mood disorders (OR = 3.3). The co-occurrence of IBS and fibromyalgia is more common in women than in men, and many patients with IBS also suffer from chronic fatigue.
As noted, generalized pain hypersensitivity is a characteristic of IBS. This has been demonstrated in adults, adolescents, and children with IBS. In a population-based study, adolescents with IBS had a higher incidence of hyperalgesia (lower heat-pain thresholds and pressure-pain threshold) compared with controls—suggesting a central sensitization process in patients with IBS.
