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Aims: An abnormal reduction in cerebral blood flow (CBF) during orthostatic stress is common in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), a condition with more prevalent joint hypermobility than in the healthy population. As one of proposed underlying mechanisms of orthostatic intolerance in hypermobile patients is vessel laxity, reducing the normal return of blood to the heart during orthostatic stress, we hypothesized that the CBF reduction during tilt-testing would be larger in ME/CFS patients with joint hypermobility than in patients without hypermobility.

Methods: In this case-control study, 100 female ME/CFS cases with joint hypermobility, who had undergone tilt-testing with CBF measurements, were compared to 100 female ME/CFS patients without joint hypermobility, matched by age and disease duration.

Results: No differences in baseline characteristics were found between groups. The hypermobile patients had significantly more postural orthostatic tachycardia syndrome (POTS) during tilt testing than the non-hypermobile ones. Compared to supine CBF, the degree of CBF reduction during the tilt was significantly larger in hypermobile cases than in the non-hypermobile controls: -32 (6)% vs -23 (7)% (p<0.0001) The larger CBF reduction in hypermobile patients was not only present in POTS patients: -33 (6)% vs -24 (4)%, but also in patients with a normal heart rate and blood pressure response to tilt testing: -31 (6)% vs -22 (9)%: (both p<0.0001).

Conclusions: ME/CFS patients with joint hypermobility syndromes have larger CBF reductions during orthostatic stress testing than patients without hypermobility. This larger CBF reduction is independent of the heart rate and blood pressure results of the orthostatic stress test.