International Consultation on Incontinence-research society defined the coexistence of overactive-underactive bladder as a real clinical syndrome for the first time in 2019. Coexistent overactive-underactive bladder (COUB) is not the fusion of the single overactive bladder (OAB) and underactive bladder (UAB). Literature lacks in many aspects about characteristics of population with COUB. 
Primary purpose of this investigation was the creation of a database including all clinical and pathological data of these patients. Finding of predictive clinical factors for early diagnosis and function of urodynamic test were secondary purposes.

Data were collected involving nine Italian hospital centers from January to December 2020. Inclusion criteria were clinical evidence of coexistence of OAB symptoms (urgency/frequency/urgency urinary incontinence) + UAB symptoms/signs (sensation of incomplete bladder emptying and/or postvoid residual [PVR] >100 ml and/or Qmax ≤12 ml/s on uroflowmetry in both men and women).
Age and sex of patients, aetiology, BMI, personal history, time of diagnosis, parity in women, urinary tract infection rate, sexual activity, previous gynecological surgery, presence, and stage of pelvic organ prolapse, stress/urgency urinary incontinence, urodynamic test, medical therapy, intermittent catheterization, advanced treatments data were collected.

Two-hundred and one patients were enrolled in the study and were divided into 2 groups based on the aetiology: 34 neurogenic and 167 non-neurogenic. The neurogenic group showed lower mean age at diagnosis than other group (p 0.0004), higher rate of urgency urinary incontinence (p 0.008) and constipation (p 0.006), lower Qmax (p 0.0001), higher PVR (p 0.0002). The non-neurogenic group (mostly women, p 0.001) presented a higher mean BMI (p 0.006). Table 1 expresses response to treatment.
Medical therapy (alpha-blockers, antimuscarinics, mirabegron and combinations) had high efficacy rate in 68% of patients (no statistically significant difference between the 2 groups). Comparing the two groups of treated versus not treated patients (31.8%), those treated had more improvements than the others, regardless of aetiology (p 0.002). 
The neurogenic group revealed higher rate of self-catheterism (p 0.002). Urodynamic test was performed in 143 patients with diagnosis of detrusorial overactivity (DO) (50.3%), detrusor underactivity (DU) (38.5%), coexistence of DO+DU (15.4%), obstruction (46.1%). Predictive factors by multivariable analysis were lower Qmax, higher PVR and lower rate of POP in women (p 0,0002; p 0,05; p 0,04 respectively).

Mirabegron achieved the best results either alone and in combination and is recommended as the first line for treatment. Intradetrusorial injection of botulinum toxin performed excellently on OAB, but also in mixed cases, saving detrusor energy in the storage phase and improving muscle contraction during voiding. Sacral neuromodulation had better results in non-neurogenic group. No predictive characteristics can be defined, and coexistent symptoms should be treated, often in combination therapy.

COUB (with or without urodynamic confirmation) is not the simple fusion of both syndromes, and a specific treatment of the pre-dominant symptoms is suggested. Urodynamic test really confirmed the coexistence of DO + DU in 15.4% of cases only, and it is recommended in doubtful situations or in non-responder patients after the first line treatment.