**1. Introduction**

Voiding dysfunction is a urological condition characterized by slow or incomplete bladder emptying [1,2]. Being a major component of lower urinary tract symptoms (LUTS) in men, voiding dysfunction is actually not uncommon in women in clinical practice [3]. Detrusor underactivity (DU) and bladder outlet obstruction (BOO) are two fundamental etiologies of voiding dysfunction and both could result from either neurogenic or nonneurogenic origins [4]. The latter could further be subdivided into anatomical obstruction and functional obstruction.

Urodynamic study is often required for the diagnosis of voiding dysfunction. Invasive urodynamic studies such as pressure flow studies or videourodynamic studies (VUDS)

**Citation:** Kao, Y.-L.; Ou, Y.-C.; Tsai, K.-J.; Kuo, H.-C. Predictive Factors for a Successful Treatment Outcome in Patients with Different Voiding Dysfunction Subtypes Who Received Urethral Sphincter Botulinum Injection. *Toxins* **2022**, *14*, 877. https://doi.org/10.3390/toxins14120877

Received: 8 November 2022 Accepted: 13 December 2022 Published: 15 December 2022

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could differentiate DU from BOO as causes of voiding dysfunction [5]. VUDS could further undermine the underlying lower urinary tract dysfunction of BOO including urethral stricture, benign prostate obstruction (BPO), high-grade pelvic organ prolapse as anatomical obstruction, primary bladder neck obstruction, or urethral sphincter dysfunction as functional obstructions [6]. The accurate diagnosis and measurement of urodynamic parameters from VUDS may predict and even improve the outcomes of different voiding dysfunctions [7].

Except for simple anatomical obstruction such as BPO or high-grade pelvic organ prolapse, treating entities of voiding dysfunction may be challenging for urologists. Botulinum toxin A (BoNT-A) has been used to treat the neurogenic voiding dysfunction since the late 1980s [8]. Urethral sphincter injection of BoNT-A could decrease urethral resistance and improve voiding efficiency (VE) via chemical sphincterotomy through the blocking of acetylcholine release from presynaptic efferent nerves at the neuromuscular junctions [9]. Benefits of urethral sphincter BoNT-A injections in non-neurogenic voiding dysfunction were also reported afterwards [10,11]. This article aims to explore the effects of urethral sphincter BoNT-A injections in different types of functional, non-neurogenic voiding dysfunction in both genders and search for the predictive factor for treatment outcome.
