Botulinum toxin as a new therapy option for voiding disorders: current state of the art

Botulinum toxin is a presynaptic neuromuscular blocking agent inducing selective and reversible muscle weakness up to several months when injected intramuscularly in minute quantities. Different medical disciplines have discovered the toxin to treat mainly muscular hypercontraction. In urology, indications for botulinum-A toxin have been neurogenic detrusor overactivity, detrusor-sphincter dyssynergia, motor and sensory urge and, more recently, chronic prostatic pain. The available literature was reviewed using Medline Services. The keywords "botulinum-A toxin", "detrusor-sphincter dyssynergia", "neurogenic bladder", "spinal cord injury", "denervation", "chronic prostatic pain", "chronic urinary retention" were used to obtain references. A toxin injection is effective to treat detrusor-sphincter dyssynergia when injected either transurethrally or transperineally. After treatment, external urethral sphincter pressure, voiding pressure and post-void residual volume decreased. The effect lasts between 2 to 9 months depending on the number of injections. Best indications seem to be multiple sclerosis and incomplete spinal cord injury patients suffering from neurogenic detrusor overactivity and detrusor-sphincter dyssynergia. According to the previous results, the use of botulinum-A toxin injections into the external urethral sphincter has been extended to a variety of bladder obstructions and to decrease outlet resistance in patients with acontractile detrusor. In cases of successful treatment, spontaneous voiding re-occurs and catheterization can be resumed. Injections of the toxin into the external urethral sphincter also seem to have a beneficial effect on chronic prostatic pain, presumably by reducing hypertonicity and hyperactivity of the external urethral sphincter. Injections of botulinum-A toxin into the detrusor muscle has first been tested to treat neurogenic detrusor activity in spinal cord injured patients and in myelomeningocele children. Long lasting (mean 9 months) detrusor relaxation occurs after injection of usually 300 units of Botox). Continence is restored in about 95% of the patients and anticholinergic drugs can be markedly reduced or even stopped. Excellent results of botulinum-A toxin injections into the detrusor in neurogenic detrusor overactivity have lead to an expansion of this treatment to incontinence due to idiopathic detrusor overactivity. Although preliminary results are promising, adequate dosage of the toxin required for this indication is not yet known. In conclusion, it appears that botulinum toxin injection into either the external urethral sphincter or the detrusor offers new promising treatment options for many different urological dysfunctions. However, large controlled trials are absolutely required to establish the role of botulinum-A toxin injections in the fields of urology and neurourology on evidence based medicine.