Diagnostic injections (blocks) are a valuable tool in the management of chronic noncancer pain. By precise blockade of specific neural structures and observation of pain responses, pain mechanisms can be accurately defined. With such information, therapeutic procedures targeting neural structures are possible. Fibromyalgia is a disorder of pain processing with characteristic symptoms. The 2010 American College of Rheumatologists fibromyalgia diagnostic criteria evaluates these symptoms in a scoring system, allowing more objectivity in the diagnosis. We hypothesize that patients with fibromyalgia phenotype fulfilling the 2010 American College of Rheumatologists criteria may respond to diagnostic blocks differently when compared to patients without fibromyalgia phenotype.
This study was designed to establish whether diagnosis or suspected diagnosis of fibromyalgia should influence the decision to perform diagnostic blocks for chronic non-cancer pain.
A prospective observational research study was performed at our institution. IRAS project ID: 231514.
Tertiary pain clinic in the UK.
Patients were selected to receive diagnostic block by usual clinical assessment after which they were asked to consent to take part in the study. All participating patients completed the 2010 American College of Rheumatologists fibromyalgia diagnostic questionnaire prior to the diagnostic block. Patients were divided into 2 groups A and B based on the outcome of block – primary outcome. Group A experienced a 70% or greater improvement in pain severity following the block for the anticipated duration of action of the local anesthetic, Group B experienced a less than 70% reduction in pain. Statistical analysis between groups A and B was conducted by comparing categorical data, described as percentages, with the chi squared test. Ordinal variables such as Widespread pain index and Symptom severity score are presented as median and analyzed with Mann-Whitney test.
Seventy-seven patients were included in the study. Two patients were lost to follow-up. Of the 75 remaining patients, 44 received lumbar medial branch blocks, 19 genicular nerve blocks, 3 blocks to nerves supplying the sacroiliac joint, one suprascapular nerve block, and 6 cervical and 2 thoracic medial branch blocks. Group A contained 38 patients and group B contained 37 patients. There was no statistically significant difference in the prevalence of fibromyalgia screening questionnaire positive patients between groups A (13 out of 38 patients) and B (13 out of 37 patients), P = 0.93. There was no statistically significant difference in the prevalence of fibromyalgia screening questionnaire positive patients in subgroups undergoing the same type of diagnostic block (spinal pain and knee pain).
Selection of patients prior to inclusion in the study may introduce bias. Patients were selected by individual treating clinicians using usual clinical practice; however, the exact selection criteria were not standardized.
We conclude that after physician selection, the presence of fibromyalgia phenotype does not influence the outcome from diagnostic block. It is likely therefore that fibromyalgia phenotype should not influence the decision to perform diagnostic blocks if indicated based on assessment by an experienced pain physician.

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