Diagnosis of fibromyalgia based on the International Classification of Diseases, 10th Revision may lead to misdiagnosis, according to a retrospective analysis of cases in a single rheumatology clinic.
Results of the study showed that clinicians failed to identify almost 50% of positive fibromyalgia cases according to the published criteria.
The study, “Diagnosis of Fibromyalgia: Disagreement Between Fibromyalgia Criteria and Clinician-Based Fibromyalgia Diagnosis in a University Clinic,” was published in the journal Arthritis Care & Research.
Recently, an increasing amount of studies have reported that fibromyalgia is overdiagnosed, with about 75 percent of the people diagnosed with the disease not satisfying the currently published criteria.
“The self-report nature of fibromyalgia symptoms facilitates the uncertainty that surrounds fibromyalgia diagnosis,” the researchers wrote.
To investigate possible diagnostic misclassification, these researchers compared expert physician diagnoses with published criteria. They considered both underdiagnoses as well as overdiagnoses.
They analyzed data from 497 patients followed at a rheumatology clinic who completed the Multidimensional Health Assessment Questionnaire (MD-HAQ), which scores on a scale from zero to three, with three indicating the worst status. Patients were also evaluated according to the 2011 modification of the American College of Rheumatology (ACR) Preliminary Diagnostic Criteria for Fibromyalgia, currently the gold standard for diagnosis, which can be used to determine a “calculated prevalence” of fibromyalgia in a given population.
“The fibromyalgia questionnaire and MD-HAQ were used together to estimate the usefulness of the MD-HAQ in the diagnosis of fibromyalgia,” they wrote.
They compared the questionnaire results to those of clinical diagnoses reached using the International Classification of Diseases, 10th Revision (ICD-10), for the diagnosis of fibromyalgia.
The ICD-10 was used at the rheumatology clinic to not only identify fibromyalgia but also other diseases, including systemic lupus erythematosus (86 patients), osteoarthritis (152 patients), and rheumatoid arthritis (88 patients).
According to the 2011 ACR criteria, 121 patients (24.3 percent) satisfied the fibromyalgia criteria, while 104 patients (20.9 percent) received a clinical diagnosis of fibromyalgia according to the ICD-10, establishing an agreement between both methods at 79.2%.
“However, agreement beyond chance was only fair,” the researchers said. The results showed that physicians failed to identify 60 criteria-positive patients (49.6%) and incorrectly identified 43 criteria-negative patients (11.4%).
Among the 104 patients with a clinical diagnosis of fibromyalgia, only 58.7% of them (61 patients) satisfied the 2011 criteria, while of the 393 patients clinicians said didn’t have fibromyalgia, 15.3% of them (60 patients) satisfied the 2011 criteria.
In the pool of patients diagnosed with rheumatoid arthritis, agreement between both diagnostic methods was 84.1%. However, of 13 rheumatoid arthritis patients with criteria-positive for fibromyalgia, only five were identified by clinicians, and six patients were wrongfully diagnosed with fibromyalgia.
Results were worse for those with systemic lupus erythematosus, with only four patients diagnosed by clinicians out of 19 with criteria-positive fibromyalgia. Of 44 patients with osteoarthritis and criteria-positive fibromyalgia, 28 were identified by clinicians.
The analysis revealed that 97.7% of the patients clinicians diagnosed with fibromyalgia were women, compared with 83.3% according to the fibromyalgia criteria. Additionally, clinically diagnosed patients had higher scores on the symptom severity scale and lower scores on the widespread pain index, two components of fibromyalgia criteria questionnaires.
“This suggests that a bias exists toward overidentification of fibromyalgia in women or in those with psychological distress, and that such a bias may distort case identification,” the researchers wrote.
Additional factors, such as a family history of fibromyalgia and the presence of additional disorders, such as irritable bowel syndrome and restless leg syndrome, may have played a role in the clinicians’ assessment.
Researchers also claimed that the increased diagnoses of fibromyalgia in patients who do not satisfy criteria may be the result of what they called extensive direct-to-patient pharmaceutical advertising, after a previous study found that fibromyalgia diagnosis in the U.S. military doubled “following advent of federally approved drugs for [fibromyalgia] in concert with pharmaceutical industry marketing.”
“We found that expert physicians in a university clinic often misdiagnose fibromyalgia when compared with published criteria, probably for a variety of reasons,” the researchers wrote.
“Misdiagnosis is a public health problem and one that can lead to overdiagnosis and overtreatment, as well as to inappropriate treatment of individuals not recognized to have fibromyalgia symptoms,” the study concluded.
“We have recently studied the same issue in 3,000 primary care patients and found about the same results. Therefore, our conclusions are secure,” Frederick Wolfe, MD, of the National Data Bank for Rheumatic Diseases and study lead author, said in a press release.
In an accompanying editorial, Don Goldenberg, MD, at the Oregon Health & Science University, however, stressed that the clinicians’ opinion is still the ultimate standard for diagnosing the disease, since it accounts for many variables that may be missed by the criteria.
“The diagnostic gold standard for fibromyalgia will continue to be the rheumatologist’s expert opinion, not classification criteria, no matter how well-refined and intentioned,” he wrote. “This is the only way to capture the variability and severity of inter-related symptoms as they play out over time.”