Are cardiac syndrome X, irritable bowel syndrome and reflex sympathetic dystrophy examples of lateral medullary ischaemic syndromes?

Altered pain appreciation and autonomic function are hallmarks of Cardiac syndrome X, Irritable bowel syndrome and Reflex sympathetic dystrophy. Both pain appreciation and autonomic function are controlled by the lateral medulla. This hypothesis proposes that lateral medullary ischaemia at a microvascular level is responsible for these syndromes and could also be linked to other conditions where autonomic dysfunction is a major feature such as late-onset asthma, type 2 diabetes and essential hypertension. Autonomic function is controlled by the nucleus tractus solitarius, which acts as the main viscero-afferent nucleus in the brain stem regulating vagal tone. It is particularly susceptible to ischaemia since it is highly metabolically active and lies in a medullary arterial watershed zone. The anatomical route of the vertebral artery through cervical vertebra makes it vulnerable to injury from whiplash with or without any genetic predisposition to atheroma formation. This could make microvascular occlusion commonplace and a plausible explanation for the above syndromes. Ischaemia rather than infarction occurs because of the excellent collateral blood supply in the brainstem. In support of this hypothesis, a new Transcranial doppler ultrasonography arterial signal has been described called small vessel knock, the ultrasound signal of small vessel occlusion. Recent evidence has shown that ultrasound targeting of this signal in the vertebral artery improves clinical symptoms in these syndromes which supports this hypothesis. Two such cases are discussed.