ObjectiveThe purpose of the research is to test the measurement of the total urinary volume, induced by the diuretic osmotic action of mannitol, in a group of symptomatic MD patients and in healthy controls.ResultsAn altered excretory urinary volume after mannitol challenge was observed in symptomatic MD (874.3 ± 302.1) compared to healthy volunteers (361.7 ± 181.6) (p = 0.0001). This easy and self-administered method might be proposed to replace the analysis of the urinary sugars’ concentration in symptomatic MD patients.