Syndrome of inappropriate secretion of antidiuretic hormone (SIADH) in a patient with multiple sclerosis.

Association of the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) with multiple sclerosis (MG) is very rare, although many other disorder of the nervous system have been reported to be associated with this syndrome; there is only one case report in the literature. We describe here a patient with the syndrome associated with MS. A 62-year-old women had a variety of neurologic symptoms, where clinical course was typical of MS. Transient episodes of hyponatremia and disturbance of consciousness occurred repeatedly with deterioration of MS. The concentration of antidiuretic hormone (ADH) was high whereas the plasma osmolality was low in the presence of concentrated urine, during the episodes of hyponatremia. Urinary Na excretions exceeded 20 mEq/day. Computed tomography and magnetic resonance imaging revealed lesions in the brain, especially in the periventricular region. The hypothalamus and pituitary appeared normal by these imaging methods. Since the periventricular region surrounds and may be functionally connected to the hypothalamus which plays the central role in the regulation of ADH secretion, it was concluded that association of SIADH and MS in this patient was not coincidental, and that demyelinating processes in the periventricular region exerted an abnormal influence on ADH secretion resulting in SIADH. Contribution of other mechanisms as increased intrathoracic pressure, however, could not be excluded completely.