**2. Bladder criteria**

### **2.1 Detrusor overactivity**

Detrusor overactivity (DO) is the urodynamic observation of involuntary detrusor contractions during the filling phase of cystometry (Abrams et al., 2002).Thus, DO can only be detected by urodynamic assessment, an invasive and expensive test. It has been demonstrated that DO was present in approximately 45% of OAB-dry and 60% of OAB-wet patients (Hashim & Abrams, 2006). As the main symptoms of OAB may suggest the presence of DO, several attempts have been made in order to correlate urgency with DO. However, in a recent study it was shown that reports of urgency sensations during filling cystometry were as likely to occur before or after an episode of DO and approximately one third of the DO events recorded were not associated with urgency (Lowenstein et al., 2009). In addition, DO, may be found in healthy individuals (Heslington & Hilton, 1996; van Waalwijk van Doorn et al., 1997; Hashim & Abrams, 2006). In fact, in the study by Hashim and Abrams 36% of the OAB patients studied (1076) did not present DO and more than 30% of individuals without OAB had DO (Hashim & Abrams, 2006). In addition, DO does not predict the response of patients to antimuscarinic treatment (Malone-Lee & Al-Buheissi, 2009). Hence, the combination of the discomfort felt by patients during an urodynamic evaluation with a low predictive value both for the diagnosis

therapy, the current mainstay for pharmacological management of OAB (Henderson & Drake, 2010; Athanasopoulos & Cruz, 2011). Nevertheless, despite significant improvement, antimuscarinics still produce important side-effects that may lead patients to discontinue treatment (Andersson, 2004; Andersson et al., 2009; Gulur & Drake, 2010). Moreover, antimuscarinics are contra-indicated for patients with narrow angle, may interfere with cognitive function and aggravate constipation (Gulur & Drake, 2010), all of which commonly occur in the typical OAB age group. More recently, the administration of vanilloids and botulinum toxin have been proposed as a possible treatment for OAB but these approaches should be taken with care as they are off-label procedures (Cruz & Dinis,

The key symptom in OAB, urgency, may often be confounded with urge to void. Urge is a normal bladder sensation, the intensity of which is proportional to the degree of bladder filling and allows the subject to fully control bladder function. Differentiation between urge and urgency may not always be an easy task for the caregiver or patients, particularly those who are cognitively impaired by age or disease (Michel & Chapple, 2009a, b). In addition, grading urgency is a difficult task to be accomplished by the clinician, even with the use of standardized questionnaires (Nixon et al., 2005; Starkman & Dmochowski, 2008). Currently, there is no objective test to diagnose OAB although several attempts have been made in order to overcome this. Here, we will review recent data proposing new biomarkers for a better characterization of OAB patients. The value of a biomarker in medicine is considerable and lies in its ability to identify the disease, back diagnostic and therapeutic decisions and establish a valuable prognosis to the condition. In addition, it will positively influence the outcome of the condition. In OAB, investigators have focused on bladder parameters (the presence of detrusor overactivity and the thickness of the bladder wall), serum proteins (the C reactive protein) and urinary elements (prostaglandins, cytokines and

Detrusor overactivity (DO) is the urodynamic observation of involuntary detrusor contractions during the filling phase of cystometry (Abrams et al., 2002).Thus, DO can only be detected by urodynamic assessment, an invasive and expensive test. It has been demonstrated that DO was present in approximately 45% of OAB-dry and 60% of OAB-wet patients (Hashim & Abrams, 2006). As the main symptoms of OAB may suggest the presence of DO, several attempts have been made in order to correlate urgency with DO. However, in a recent study it was shown that reports of urgency sensations during filling cystometry were as likely to occur before or after an episode of DO and approximately one third of the DO events recorded were not associated with urgency (Lowenstein et al., 2009). In addition, DO, may be found in healthy individuals (Heslington & Hilton, 1996; van Waalwijk van Doorn et al., 1997; Hashim & Abrams, 2006). In fact, in the study by Hashim and Abrams 36% of the OAB patients studied (1076) did not present DO and more than 30% of individuals without OAB had DO (Hashim & Abrams, 2006). In addition, DO does not predict the response of patients to antimuscarinic treatment (Malone-Lee & Al-Buheissi, 2009). Hence, the combination of the discomfort felt by patients during an urodynamic evaluation with a low predictive value both for the diagnosis

2007; da Silva & Cruz, 2009).

neurotrophins).

**2. Bladder criteria** 

**2.1 Detrusor overactivity** 

and successful outcome of OAB treatment impedes the routine use of urodynamic assessment for the majority of OAB patients. In a recent study, investigators tried to identify the presence of involuntary detrusor contractions through near-infrared spectroscopy (NIRS), a noninvasive method (Farag et al., 2011a; Farag et al., 2011b). NIRS is an imaging technique that can be used to monitor haemodynamic events. As the name indicates, it uses light in the nearinfrared area, which is able to penetrate the skin. It is absorbed by oxyhaemoglobin and deoxyhaemoglobin, the levels of which can reflect oxygen consumption. In those studies, investigators were able to demonstrate that detrusor contractions were accompanied by changes in those chromophores (Farag et al., 2011a; Farag et al., 2011b). The overall specificity of NIRS to detect DO was 86% when measuring oxyhaemoglobin, 80% for deoxyhaemoglobin and 72% for the sum of both chromophores. Despite obvious limitations, such as the inclusion of more men than women, results are interesting and deserve further investigation.

#### **2.2 Bladder wall thickness/Detrusor thickness (BWT/DT)**

In patients with bladder outlet obstruction, the thickness of the total bladder wall or simply the thickness of the detrusor layer was shown in several studies to be significantly increased in OAB patients when compared with healthy volunteers (Hakenberg et al., 2000; Oelke et al., 2006; Oelke et al., 2007). Hence, it was forwarded that BWT/DT could be influenced by the work overload of the bladder wall introduced by DO. Indeed, some authors have reported a trend of increasing DT associated with the severity of urgency as reported by Panayi and coworkers (Panayi et al., 2010). Khullar and co-workers analysed the total BWT via transvaginal ultrasound in a group of female patients with idiopathic DO (Khullar et al., 1996). They found that 58.7% of all analysed subjects had a mean BWT greater than 5 mm, 94% of which had DO. Only 1.6% of subjects had DO with a BWT of 3.5 mm or less. The authors proposed that the measurement of mean BWT by transvaginal ultrasound, with a cut-off of 5mm, is a suitable screening method (Khullar et al., 1996). In addition, by determining BWT also with transvaginal ultrasound, Kuhn and co-workers were able to differentiate between women suffering from stress urinary incontinence or bladder outlet obstruction (Kuhn et al., 2011). In OAB patients, DWT was reduced after anti-muscarinic treatment (Liu et al., 2009b; Kuo et al., 2010b). In addition, a positive correlation has been found between the presence of OAB and high BWT/DT(Robinson et al., 2002; Kuo, 2009).

However, the reliability of DT as a marker for DO or OAB is still debatable. BWT/DT are typically measured by ultrasound. One particular problematic issue is the well-known bias associated to the different operators of ultrasound. Another unsolved issue regards the best way to measure BWT/DT. Should the bladder be empty of filled? If filled, at which volume? Should one use an abdominal or transvaginal approach? Which are the costs? In addition, several studies failed to demonstrate significant differences between healthy controls, patients with DO, bladder outlet obstruction or with increased bladder sensation (Blatt et al., 2008). More recently, Liu et al measured the DT in normal controls and patients suffering from OAB or interstitial cystitis (Liu et al., 2009b). They found a wide variation amongst all groups of individuals with a trend of higher BWT/DT in OABwet patients that did not reach statistical significance. In another study, no differences in the BWT/DT were found between OAB patients and individuals with no OAB symptoms (Chung et al., 2010).

Biomarkers in the Overactive Bladder Syndrome 193

reporting the presence of histological signs of inflammation in biopsies from OAB patients (Comperat et al., 2006; Apostolidis et al., 2008). However, confirming the presence of inflammation through biopsies is certainly an invasive procedure not exempt of morbidities. The detection of signs of inflammation in the urine of OAB patients is a more attractive alternative. Tyagi and co-workers have recently collected urine samples from patients and determined the levels of various cytokines, chemokines, growth factors and soluble receptors (Tyagi et al., 2010). Using a luminometry-based assay, they found a significant increase, when compared with controls, in the concentration of various elements, including the monocyte chemotatic protein-1 (MCP-1), the soluble fraction of the CD40 ligand, the macrophage inflammatory protein (MIP-1β) and interleukins 10, 5 and 12. Another group of researchers also analysed of urine samples from healthy individuals and OAB patients using a proteomic approach (Ghoniem et al., 2011). Interestingly, their results indicate that while the concentration of certain elements increases (such as interleukin 16), the concentration of others decreases (such as interleukin 7). Thus, the actual role of all of these cytokines in OAB

Neurotrophins are tissue-derived trophic factors necessary for the embryonic differentiation, survival and maintenance of neuronal cells both in the peripheral and central nervous system (Pezet & McMahon, 2006). The most well studied neurotrophins are Nerve Growth Factor (NGF) and Brain Derived Neurotrophic Factor (BDNF). They exert their effects via their specific tyrosine kinase (Trk) receptors. NGF binds to TrkA while TrkB is the receptor of BDNF. Both TrkA and TrkB are present in the bladder urothelium and sensory afferents innervating the organ (Qiao & M.A. Vizzard, 2002; Murray et al., 2004).

NGF has attracted considerable attention in the Urology field. It is accepted that NGF is produced by detrusor muscle cells and by the urothelium (Steers et al., 1991; Steers et al., 1996; Clemow et al., 1997; Clemow et al., 2000; Steers & Tuttle, 2006). In humans and in rodents, the production of NGF in the lower urinary tract and in the neuronal circuits regulating bladder function is increased in pathological conditions, including cystitis and spinal cord injury (Lowe et al., 1997; Vizzard, 2000; Murray et al., 2004). In addition, exogenous NGF is known to induce bladder overactivity, irrespective of the route of delivery (Lamb et al., 2004; Yoshimura et al., 2006; Zvara & Vizzard, 2007). Likewise, manipulation of NGF levels improves bladder function and referred pain in rats with

Recent studies have demonstrated the presence of NGF in the urine of OAB patients (Kim et al., 2005; Kim et al., 2006; Liu & Kuo, 2008; Liu et al., 2009a, b; Liu et al., 2009c; Jacobs et al., 2010; Liu et al., 2011a). Levels were significantly higher than in healthy individuals and subsided after successful treatment with antimuscarinics (Liu et al., 2009b) or botulinum toxin-A (Liu et al., 2009a), in parallel with a decrease in the USS score. Based on these results, some authors have forwarded the use of NGF as presumed biomarker for OAB (Kuo et al., 2010a). Nevertheless, caution should be advised as most studies have not been placebo

is far from being well understood, undermining its utility as biomarkers.

**3.3 Neurotrophins** 

**3.3.1 Nerve Growth Factor (NGF)** 

cystitis (Hu et al., 2005; Frias et al., 2009).

controlled which may hamper the interpretation of results.

Clearly, the measurement of BWT or DT by ultrasound faces some drawbacks that are not yet overcome. Intra- and inter-operator variability in ultrasound measurements is probably the most important one. The use of different ultrasound probes, as well as in the resolutions of ultrasound-generated images (Kuo, 2009), is another limiting factor to the use of BWT/DT as a biomarker. Although clinically appealing, more studies are necessary before it becomes a tool for daily practice.
