Associated findings are mitral valve prolapse, and gastrointestinal illness including irritable bowel disease. A subgroup of mitral valve prolapse patients are known to have autonomic dysfunction including a hyperadrenergic state while abnormal serotoninergic pathways are one source of neuro-intestinal dysfunction in irritable bowel disease. The relationship of symptoms to orthostasis is a key aspect of orthostatic intolerance although some patients may experience symptoms during sitting as well as while standing. Therefore history taking is critical. Chronic orthostatic intolerance occurs with chronic failure of the autonomic nervous system as in primary autonomic failure, multiple system atrophy, and secondary autonomic failure in diabetes and Parkinsonism, but, with the exception of familial dysautonomia, these are rare events in children.
Some patients have severe hypotension.
Patients run the gamut from minimally affected to seriously disabled. Our preliminary data in adolescents and the work of others have shown a form of orthostatic intolerance with uniquely abnormal neurovascular physiology related to other forms of orthostatic intolerance. Indeed, the only effective treatment for CFS in adults and children seems to target orthostatic intolerance. The cardiovascular form taken by OI in these syndromes is distinct in producing low blood pressure without overt fainting but with severe, often disabling postural symptoms associated with tachycardia. This is particularly obvious in those with the worst clinical symptoms.