Several authors have shown that women with refractory detrusor overactivity (RDO) are found to experience bacterial cystitis in 30-40% of cases. The associated inflammatory response with release of cytokines may increase the sensitivity of local afferent nerves and contribute to patient urgency. The aim of our study was to observe any differences in concentrations of a range of cytokines in the urine of RDO patients both with and without bacteriuria.

Midstream urine (MSU) samples were collected with careful labial toilet from postmenopausal women (>50 years) attending outpatient clinics, with a portion sent to the microbiology department for culture. Genuine stress incontinence (GSI) or prolapse patients with sterile urine were controls. RDO patients with normal voiding function were subdivided into three groups: (1) no growth (RDO NG), (2) Urinary tract infections (RDO UTI); e.g. the presence of a single bacterial species >106 CFU/mL, or (3) patients with mixed growth (RDO MG); more than one bacterial species isolated +/- epithelial cells, +/- pyuria. Mixed growth was included in view of recent PCR studies showing that mixed bacteriuria may become pathogenic [1]. 

A broad selection of 27 cytokines were analysed using a Human Cytokine 27-plex Assay (Bio-Rad). Urinary cytokines were grouped into pro-inflammatory, chemokines and regulatory cytokines based on their known clinical properties; results were compared between each clinical group. A history of recurrent UTI was defined as >3 infections in 12months. Analysis was by Mann-Whitney test.

Urine was collected in 45 controls and a consecutive series of 95 women with RDO, subdivided into RDO NG (n=48), RDO MG (n=28), and classical UTI (RDO UTI n=19). The median age of control (71, IQR 62-75.5) and RDO groups (70, IQR 61-78) were similar. 

The RDO group with sterile urine (RDO NG) was found to express four cytokines at significantly higher concentrations than the control group (Table 1). RDOs with current proven UTI had significantly higher cytokine levels in 17/27 assays. Similarly, the presence of mixed growth in RDO patients was associated with elevated cytokines in 11/27 assays. Patients with RDO and a previous history of recurrent UTI and current UTI had markedly increased cytokines in 12/27 assays. No difference was noted between all groups for the expression of IL-9, IL-10, IL15, IFN-γ, VEGF, MCP-1 (data not shown in Table 1).

A major finding of this study is the breadth of the pro-inflammatory cytokines, chemokines and regulatory factors that are elevated in women with refractory DO. It was interesting to note that in RDO women with uninfected urine there were four cytokines that were elevated compared to control samples. These four cytokines (IL-5, IL-12p70, IL-17A and GM-CSF) show persistent elevation across all bacteriuria groups. 

With the exception of GM-CSF, these factors are not commonly associated with the immune response to infection [2]. These cytokines are however associated with activity of innate lymphoid cells (ILC) [3]. ILC’s are newly discovered immune cells that play a key role in maintain the balance between inflammation and inflammatory disease [3]. For example, IL-12p70 activates ILC class 1 cells, IL-5 activates ILC class 2 cells which are associated with allergic asthma and IL17A is produced by ILC class 3 cells and is associated with Crohn’s disease [3].

Previous studies of cytokine signals in women with urge incontinence have mainly focused on patients with newly diagnosed OAB. In this study of 95 women with urodynamically proven refractory DO and 45 age matched controls, our investigation of 27 cytokines have shown that refractory DO women with no UTI still had significant elevation four cytokines that are associated with activation of innate lymphoid cells. The refractory DO women with UTI have significant elevation in 17 of 27 cytokines.  

To our knowledge this is the most definitive study of cytokine levels of refractory DO women, in relation to UTI status. Our findings support the notion that increased cytokine signalling may enhance the sensitivity of afferent nerves and promote distressing urgency symptoms. Antimuscarinic medications do not target this mechanism and thus the refractory state may persist.

Thomas-White K.J., et al (2016). Incontinence medication response relates to the female urinary microbiota. International Journal of Urogynecology, 27:723-733.
Sundac et al., (2016) Protein-based profiling of the immune response to uroprathogenic Escherichia coli in adult patients immediately following hospital admission for acute cystitis. Pathogens and Disease. 74. ftw062.
Ebbo, M., et al (2017). Innate lymphoid cells: major players in inflammatory diseases. Nature Reviews: Immunology. 17(11): 665-678.