Prevalence of lower urinary tract symptoms (LUTS) in patients with multiple sclerosis (MS) increases with disease duration. Current management of urinary clinical symptoms in MS is mainly conservative. Its long-term outcome is often poor because of the progressive disease course and the treatment related side effects. Alternative therapeutic options are botulinum toxin injections, electrical stimulation of dorsal penile/clitoral nerve, and sacral nerve modulation. Posterior tibial nerve stimulation (PTNS) is a second minimally invasive method of electrical stimulation. Multiple benefits may derive from the development and validation of a dedicated protocol of a new self-activated neuromodulation therapy, which may improve therapy compliance/effectiveness, quality of life and social life in MS patients with refractory LUTS. Furthermore, it may contribute to reduce outpatient visits, health costs and work absenteeism.

Inclusion Criteria:

1. Male or female aged 18 - 80;
2. Diagnosis of multiple sclerosis according to McDonald [20];
3. Clinical stability over the past 6 months (no relapses and no disability progression, defined as worsening of ≥1 point in the EDSS score if reference EDSS is ≤5.5, and ≥0.5 points if reference EDSS is>5.5);
4. One or more of: urinary frequency greater than 8 times/24 hours, urinary urge incontinence at least 2 episodes in 24 hours on 3-day voiding diary;
5. Urodynamic diagnosis of detrusor over-activity (DOA)and / or detrusor-sphincter dyssynergia (DSD);
6. Previous failure of conservative treatments (challenge over ≥6 months) i.e. lifestyle modification-fluid consumption, behavioral modification, and pharmacological therapy and stable OAB medications for at least 30 days;
7. No pharmacological treatment of overactive bladder (antimuscarinics and beta-3 agonists) for 2 weeks prior to screening;
8. Positive response to ongoing PTNS treatment defined as ≥50% reduction in urinary frequency, and/or ≥50% fewer incontinence episodes, or a return to normal voiding frequency (<8 voids/day), based on retrospective diary review (treatment compliant and non-compliant patients) or PTNS treatment naïve able to sense tibial nerve stimulation (to be tested with TENS exam).
9. Competent sphincter mechanism and normally functioning upper urinary tract;
10. Leg circumference in the range of 20-30 cm at implantation site;
11. No contraindications for surgical intervention (e.g. being immunocompetent, no anticoagulant treatment, no current infection);
12. For female patients: using effective contraceptive methods;
13. Ability to comply with study requirements;
14. Having provided written informed consent.

Exclusion Criteria:

1. Previous participation in another study with any investigational drug or device within the past 90 days;
2. Any metal implant in the area of StimRouter lead implantation site;
3. Anatomical defects that preclude use of the device;
4. Treatment with botulinum toxin injections, urinary incontinence surgery or implantation of artificial graft material, spinal or genitourinary surgery, abdominoperineal resection of the rectum or radical hysterectomy (female)/ prostatectomy (male) within the last 6 months;
5. Previous treatment with sacral neuromodulation;
6. Diagnosis of pelvic pain disorders, stress incontinence, current urinary tract infection, urinary stone and/or urinary tract malignancy; cystocele, enterocele or rectocele of grade 3 or 4;
7. Critical limb ischemia;
8. Previous or current pelvic radiotherapy and/or chemotherapy;
9. Severe uncontrolled diabetes;
10. Being prone to excessive bleeding;
11. Having a pacemaker or implantable defibrillator or other neural stimulation systems;
12. Exposure to diathermy or electrocautery;
13. Clinically significant peripheral neuropathy;
14. Neutropenic or immune compromised;
15. Pelvic radio- and/or chemotherapy;
16. Morbid obesity (BMI >40);
17. Pregnant or lactating women, or women planning a pregnancy during the study, <9 months post-partum;
18. Male: alpha-blocker for benign prostatic hyperplasia;
19. Allergy to local anesthetic or adhesive;
20. Life expectancy <1 year.