Ehlers-Danlos Syndrome (EDS) and Postural Orthostatic Tachycardia Syndrome (POTS) are complex, chronic conditions that frequently occur together. EDS is a disorder of the body’s connective tissue, while POTS is a disorder of the autonomic nervous system, which controls involuntary functions like heart rate and blood pressure. The significant overlap suggests a direct physiological link, where the underlying structural defect of EDS triggers the autonomic dysfunction seen in POTS.
Defining the Conditions and Their Common Association
Ehlers-Danlos Syndrome is a group of inherited disorders that affect the connective tissues, which provide structure and support throughout the body, including the skin, joints, and blood vessel walls. The most common form associated with POTS is hypermobile EDS (hEDS), characterized primarily by joint hypermobility, tissue fragility, and chronic pain. EDS symptoms stem from defects in the production or processing of collagen.
Postural Orthostatic Tachycardia Syndrome is a form of dysautonomia, a malfunction of the nervous system that regulates automatic bodily functions. The hallmark of POTS is an abnormal increase in heart rate—typically 30 beats per minute (bpm) or more in adults—upon standing up, without a significant drop in blood pressure. This rapid heart rate causes symptoms like dizziness, lightheadedness, fatigue, and “brain fog.” The co-occurrence of these conditions is remarkably high; studies suggest that up to 80% of individuals with hEDS experience symptoms consistent with POTS.
The Role of Faulty Connective Tissue
The root cause of EDS lies in the genetic variations that compromise the body’s collagen and elastin, the materials responsible for tissue strength and elasticity. This flawed structural material means that connective tissues throughout the body lack the necessary firmness and resilience. This structural weakness also affects internal scaffolding, including the walls of blood vessels.
Connective tissue forms a supportive matrix around veins, which are the blood vessels responsible for returning deoxygenated blood to the heart. When this perivascular connective tissue is weakened in EDS, it provides inadequate external support to the vessel walls. This lack of firm scaffolding is the initial structural predisposition that sets the stage for circulatory problems. The result is a system of blood vessels, particularly veins, that are inherently too compliant, meaning they are overly stretchy and distensible.
Vascular Compliance and Autonomic Dysfunction
The overly compliant veins, a direct consequence of the faulty connective tissue, are unable to effectively constrict against the force of gravity when a person stands upright. Instead of maintaining their shape, these veins in the lower body, such as the legs and abdomen, widen excessively. This widening causes a significant amount of blood to pool in the lower half of the body, a phenomenon known as venous pooling.
This excessive pooling drastically reduces the amount of blood returning to the heart, which is known as reduced venous return or reduced preload. The heart then has less blood to pump out, leading to a temporary drop in central blood volume and cerebral blood flow.
The body’s autonomic nervous system (ANS) interprets this sudden decrease in blood return as a state of shock or hemorrhage, triggering an immediate and exaggerated compensatory response. The ANS tries desperately to restore blood flow to the brain by activating the sympathetic nervous system, the body’s “fight-or-flight” branch. This sympathetic surge releases hormones like norepinephrine, causing the heart to beat much faster and harder, resulting in the characteristic tachycardia of POTS. The rapid heart rate is the heart’s attempt to pump the reduced blood volume quickly enough to compensate for the blood trapped in the overly compliant lower body veins.
Contributing Factors and Symptom Amplification
While the structural weakness of the vasculature is the primary mechanism linking EDS to POTS, other factors common in this patient population can significantly amplify the severity of symptoms. Many individuals with EDS and POTS also experience hypovolemia, a condition defined by a low absolute blood volume. This reduced volume makes the effects of gravitational pooling even more pronounced and harder for the body to overcome.
Another common co-occurring condition is Mast Cell Activation Syndrome (MCAS), which involves the inappropriate release of inflammatory mediators from mast cells. These mediators, such as histamine, can cause vasodilation, or widening of the blood vessels, further destabilizing blood pressure regulation. The co-existence of these three conditions—EDS, POTS, and MCAS—is often referred to as a “triad,” combining structural weakness, low blood volume, and unstable vessel tone.