Pathophysiology of urinary dysfunction in multiple sclerosis

Bladder and urethra are innervated peripherally by pelvic parasympathetic, lumbar sympathetic and pudendal nerves; but a complex of brain networks is involved in the micturition cycle and the pontine micturition centre (PMC) has a fundamental role. Bladder storage is secondary to activation of beta- and alpha-receptors with simultaneous inhibition of parasympathetic transmission and increased somatic discharges via the pudendal nerves. Bladder voiding involves coordination of sacral parasympathetic stimulation of the bladder, inhibition of sympathetic outflow and pudendal somatic outflow to the external striated sphincter. Lesions of the brain above the PMC are usually associated with detrusor overactivity; medullary lesions are characterised by urodynamic detrusor overactivity associated with detrusor-external sphincter dyssynergia. Sacral lesions can produce bladder areflexia and/or hypocontractility.