Pain is not considered to be a characteristic of overactive bladder (OAB), but mechanisms underlying pain perception, and afferent hypersensitivity are thought to contribute to the clinical manifestations of OAB. It should be kept in mind that these patients may present with symptoms similar to chronic pain syndromes considering that central sensitization is one of the pathophysiological mechanisms in OAB (1).  In the current study, we aimed to examine the pain characteristics of women with OAB in order to determine the evidence of central sensitization in OAB pathophysiology, and to investigate whether they are different from healthy women.

The study was conducted between October 2018 and March 2019 prospectively, after ethical approval was obtained (KA18-281). A total of randomized 56 participants (28 OAB patients, and 28 healthy volunteers) who were evaluated for "Primary Outcome Measures" and "Pressure Pain Threshold" measurements were included in the study, according to the sample size power analysis determined with 95% power, and 0.05 error margin. Pain intensity and quality were evaluated with ‘’The Short Form of the McGill Pain Questionnaire’’. ‘’Self-Leeds Assessment of Neuropathic Symptoms, and Signs (LANSS)’’ were used to assess the presence of neuropathic pain, and pain threshold were evaluated with ‘’Algometer’’. ‘’8-item Overactive Bladder Questionnaire (OAB-V8)’’, ‘’Incontinence Impact Questionnaire-7 (IIQ7)’’ and ‘’Urogenital Distress Inventory-6 (UDI6)’’ were used to evaluate OAB symptoms. ‘‘Nottingham Health Profile’’ questionnaire was used to determine quality of life.

According to algometer, the measurement sites such as; symphysis pubis, right spina iliaca anterior superior (SIAS) anteromedial, right SIAS inferomedial, left SIAS inferomedial, right costachondral, left costachondral, right lateral epicondylitis, left lateral epicondylitis, right knee medial pillow, left knee medial, right occiput, right trapezius, left trapezius, right supraspinatus, left supraspinatus, right gluteus, left gluteus, right thoracanter major, and left thoracanter major exhibited statistically significant difference in OAB patients (p<0.05). Conversely, there was no difference in left SIAS anteromedial, right lower cervical, left lower cervical and left occiput sites (p>0.05).
There was found a statistically significant strong correlation between the McGill Short Form Questionnaire, and IIQ7 (r=0.666), OABV8 (r=0.640), and LANSS (r=0.610), whereas there was a statistically significant moderate correlation with UDI6 (r=0.576) (Table 1). According to ‘’The Short Form of the McGill Pain Questionnaire’’ for to evaluate the characteristics of pain showed that the median sensory sub-scale value was 6.5, the affective sub-scale value was 2, and the total value was 9 with a pain intensity of 4.6 cm. In the healthy controls, the median of all these values was found to be zero (p=0.001). The evaluation of the results of the LANSS scale, which was applied for the presence of neuropathic pain showed that the mean score was 10.86±6.49 in women with OAB, and 0.21±0.63 in the healthy controls (p=0.001) (Table 2).
Nottingham Health Profile showed significant difference in pain (p=0.001), sleep (p=0.003), social isolation (p=0.046), physical activity (p=0,001), energy (p=0.001), and in the total scores of part 1 (p=0.001) and part 2 (p=0.001) for OAB patients.

Reynolds et al. reported that a significant proportion of patients were accompanied by OAB with extensive body pain, which they explained to be the result of central sensitization. The authors also emphasized that comorbid central sensitization symptoms should be evaluated with respect to comorbidity in patients with OAB (2). There are no studies in the literature examining the changes in pain threshold, which is an important determinant of central sensitization in patients with OAB. These patients report pelvic pain accompanied by urinary urgency, and sensations of discomfort and pressure, in addition to predisposition to body-wide pain (2). For this reason, we performed pain threshold measurements of the patients both from the anatomical localizations in the pelvis and from the anatomical localizations of the sensitive points as defined in fibromyalgia to determine the whole-body pain. In the current study, the comparison of the pain threshold measurements in OAB patients with the healthy controls demonstrated that the pain threshold was lower in the anatomical locations such as anteromedial, and inferomedial of the superior symphysis pubis, anterior superior of the iliac spine and inferomedial in the pelvis, and at 18 sensitive points defined by fibromyalgia. It was shown that the pain intensity in OAB patients increases in parallel with the severity of symptoms, which supports this result. This increase occurred in both affective and sensory scales of pain. The result of our study, which supports the pathophysiology of central sensitization, is highly significant with respect to contributing to the literature.

The comparison between the women with OAB and healthy controls demonstrated that there was a decrease in pain threshold in respect of Algometer measurements. It was determined that there was an increase in the intensity of sensory and affective characteristics of pain. This result, independent of the effect of OAB on emotional state, confirms the theorem that central sensitization predisposes to pain syndromes in the pathophysiology of OAB.

McKernan L, Cohn J, Bruehl S, Dmochowski R, Reynolds WS. Overactive bladder and co-occurring interstitial cystitis/bladder pain syndrome: The role of central sensitization in the clinical presentation. Journal of Urology, Vol. 197, No. 4S, Supplement, Saturday, May 13, 2017.
Reynolds WS, Dmochowski RR, Wein A, Bruehl S. Does central sensitization help explain idiopathic OAB? Nature Review Urology. 2016; 13(8): 481-91.