## 1 Introduction  
Chronic pelvic pain (CPP) is defined as a chronic or persistent pain perceived in structures related to the pelvis of either men or women, lasting for at least six months. It is often associated with negative cognitive, behavioral, sexual, and emotional consequences as well as with symptoms suggestive of lower urinary tract, sexual, bowel, pelvic floor or gynecological dysfunction. Causes may include local pathology such as infections, malignancy or primary anatomical, functional or neurogenic disease of the pelvic organs. Otherwise, when there is no evidence of proven underlying disease accounting for the pain, it refers to a chronic pelvic pain syndrome (CPPS) [1].  
The etiology of CPP is difficult to determine, as the physiopathology is complex and may vary between patients' population and disease subtype. Several theories and associated findings are currently under investigations [2]. Both animal and clinical studies have historically evaluated the physiopathology of this syndrome proposing mechanisms in which pain is maintaining even in the absence of peripheral stimuli or a recognized pathology [3]. Moreover, it is difficult to assess the real prevalence of CPPS, considering both sexes and all types of subclassification, mainly because of the different diagnostic criteria and the overlapping symptoms with other diseases. A few studies have tried to investigate the prevalence of CPP, and with different results. [PERSON] et al. reported a prevalence of CPP among US women aged 18-50 years around 14.7%, and in more than half of cases the etiology was unknown [4]. In a more recently study, [PERSON] et al. described a prevalence of symptoms suggestive of CPP of 5.7% and 2.7% in women and men, respectively [5].  
The management of CPPS is based on a bio-psychosocial model which includes an active patients' involvement. Pharmacological and non-pharmacological interventions such as psychotherapy, physiotherapy, drugs and invasive treatments rarely works in isolation and often need to be considered together as a part of a personalized treatment strategy [1; 6].  
Botulinum toxin is currently used for the treatment of various pain disorders. It is a neurotoxin well known due of its action that blocks the exocytosis of the acetylcholine on the presynaptic cholinergic peripheral nerves. This ends in a skeletal muscle relaxation and in an analgesic effect. There are seven different types of botulinum neurotoxins, named from A to G [7]. The serotype A (BTX-A) was first investigated in 1990 for the treatment of detrusor external sphincter dyssynergia in patients with spinal cord injuries [8]. Few years later it was used against neurogenic detrusor overactivity. Nowadays neurotoxin A is also used as a third line treatment against non-neurogenic overactive bladder [9]. International guidelines already considered BTX-A, for the management of chronic prostatitis (CP)/prostate pain syndrome (PPS) and functional anorectal pain [1]. However, there are conflicting results in literature, among studies assessing the real effect of BTX-A in the treatment of CPP. Aim of this systematic review is to investigate the efficacy of BTX-A injection in CPPS management.