Multiple sclerosis causes demyelinating lesions, which can induce multiple symptoms. If motor disorders are the most visible disability, urinary disorders are frequent, with prevalence from 32 to 86%. The first ones are due to pyramidal, cerebellar or proprioceptive lesions. The seconds are due to specific lesion in inhibitor/activator encephalic centers, or interruption on medullary conduction. It seems to be evident that walk and urinary disorders are link, because of similar anatomic ways and control process. Effect of bladder filling is well known on motoneuronal excitability. The effect of bladder filling on walk stay unknown, while medullary integration of these two functions is very close, in medullary cone.

Primary aim is to assess the effect of need to void on walk speed in multiple sclerosis with lower urinary tract symptoms. Secondary aim is to identify clinical or urodynamic factor link with major walk impairment when patients need to void.

Patient with multiple sclerosis over 18 years old, consulting for lower urinary tract symptoms in a tertiary center are included.

History and treatment, high, weigh, symptoms severity by USP score, cognitive impairment by MMSE score and last urodynamic data are recorded. Patient are asked to drink water until they feel a strong need to void, for which they would go to urinate at home.

Walk tests are realized in a specific place, with calm and no passage. A chair is placed at each end of the path. Toilets are just next to the hall where they realize the tests. A 10 Meters Walk Test is done during this condition, 3 times (only the intermediate 6 meters are recorded). They can take 30 seconds of rest between each try if necessary. One Timed up and go is done. Patient can use their habitual walking device. Speed walk asking is comfortable for the two test.

Next, patient can urinate. 3 post void residual volume with portable echography are done, and the higher is recorded.

Patient achieve the same walk tests after urinate, in the same order. They must use the same walking device.

Primary outcome is mean gait recorded for 10 meters walk test.

Secondary outcome is time for timed up and go test.

Individual variability between the 3 10MWT in the two conditions will be study.

Influence of age, EDSS, severity of symptoms, MMSE, detrusor overactivity on speed impairment will be study in secondary analysis.

Inclusion Criteria:

• Multiple sclerosis
• Follow in neuro-urology for lower urinary tract symtpoms
• Able to walk 50 meters without human assistance
• able to hold on void during 3 minutes at least

Exclusion Criteria:

• actual urinary tract infection
• relapse in the last week
• Mini Mental State Examination < 10

Patients consulting in a tertiary center in neuro-urology