The effect of dihydroergotamine on venous distensibility and blood pressure in idiopathic orthostatic hypotension.

We report a case of severe idiopathic orthostatic hypotension (IOH) documented by direct, continuous, ambulatory blood pressure monitoring. Failure of vasoconstriction and more significantly of venoconstriction in response to upright posture was demonstrated, indicating an autonomic nervous system disorder. The venoconstrictive agent dihydroergotamine (DHE) had little effect in preventing a fall in forearm venous tone with head up tilting but caused a recumbent pressor response leading to side effects. These were noted at a time of low plasma DHE levels indicating denervation hypersensitivity. Difficulties may arise in using DHE to treat severe cases of IOH who have denervation hypersensitivity.