We present a 41-year-old male with vertigo due to orthostatic hypotension caused by diabetic neuropathy. Autonomic function test showed no increase in either plasma noradrenaline or sympathetic activity in response to standing up. During head up tilting, vertebral blood flow measured by Doppler flowmeter decreased with a decrease in blood pressure and asymmetrical vertebral blood flow was evident. Head up tilting also induced nystagmus and vertigo. After the patient was treated for orthostatic hypotension by L-threo-3, 4-dihydroxyphenylserine, a precursor of noradrenaline, neither asymmetrical vertebral blood flow nor nystagmus were observed during head up tilt. It is suggested that asymmetrical vertebral blood flow induced by sympathetic dysfunction causes asymmetrical excitability of the vestibular system, resulting in nystagmus and vertigo.
