The observation, stated once
These three are diagnosed together often enough to have earned a nickname in clinic — which is where most explanations stop.
Through the mechanism
Start with the tissue. Compliant vessel walls hold more blood below the heart on standing, so the upright reflex has less venous return to work with and compensates with heart rate.
Mast cells are resident in that same connective tissue matrix, physically embedded in it and against its small nerve fibers. Tissue differences and mast-cell behavior are not neighbors by accident.
Mediator release lowers vascular tone, which worsens the orthostatic problem, which raises sympathetic drive, which lowers the threshold for further release. The loop closes.
Nothing here requires three separate diseases to have arrived by coincidence. One matrix with three downstream expressions accounts for the pattern more economically.
What it changes in practice
- Improving any one arm usually improves the others — compression helps reactivity, mediator control helps standing.
- Care needs a coordinator, because the three specialists involved rarely see the same notes.
- Sequence interventions and change one thing at a time, or nothing is attributable.
Hold this loosely
The shared-mechanism account is coherent and increasingly supported, but the trifecta is still a clinical observation rather than a validated entity.