A 67-year-old man with
SIADH complicated by slowly progressing autonomic failure was described. The patient noticed
constipation at the age of 57. In the following years, he suffered from
urinary incontinence, depletion of sweating,
impotence,
sleeplessness with snore, and
dizziness while walking. Physical examination revealed a masked oily face with slight cerebellar disturbance. Abnormality of autonomic function tests was recognized and he was diagnosed as
Shy-Drager syndrome with gradually progressing, diffuse autonomic failure accompanied by slight
cerebellar ataxia and
Parkinsonism. Both serum
sodium level and plasma osmotic pressure were reduced, whereas daily
sodium excretion was more than 100mEq and urinary osmolality was about 500mOsm/kgH2O. His renal function was intact, and the adrenocortical and
thyroid hormone levels were normal, then criteria of
SIADH was fulfilled.
SIADH was thought to have occurred on the basis of
Shy-Drager syndrome. Water load test showed failure of adequate water diuresis, but intravenous
phenytoin administration following the water load test ameliorated the diuresis to normal. The relationship between plasma osmolality and the ADH response indicates that ADH was adequately secreted in response to the increase in plasma osmolality but not suppressed in response to the decrease in plasma osmolality below 280mOsm/kgH2O. These results suggest that ADH synthesis in the hypothalamus and its secretion from the pituitary gland were both intact. The response of ADH secretion to the
orthostatic hypotension induced by head-up tilt was quite blunted, being compatible with
Shy-Drager Syndrome. Sleep disturbance was studied by polysomnography and laryngoscopy, and was revealed to be based upon severe
sleep apnea due to incomplete
paralysis of the bilateral vocal cords.
Sleep apnea due to
vocal cord paralysis is sometimes found to be complicated in patients with
multiple system atrophy (MSA) including
Shy-Drager syndrome, and is known as
Gerhardt syndrome. This is the first report on a case of
Shy-Drager syndrome complicated with
SIADH and bilateral
vocal cord paralysis. In this case,
SIADH is caused by impaired afferent pathways from baroreceptors to the hypothalamus, which transfer inhibitory stimuli on ADH secretion. It is suggested that
Shy-Drager syndrome should be considered one of the causes of
SIADH.