Postural orthostatic tachycardia syndrome (POTS) is classified into different types. It is important to understand the difference between these because the treatment differs depending on the type of POTS diagnosed. The most often discussed types of POTS are neuropathic POTS and hyperadrenergic POTS; however, there is also a form of POTS called Secondary POTS.
Neuropathic basically means nerve disease. The nerve supply to the vessels in the lower limbs known as the sympathetic nerves is responsible for stimulating the vessels to tighten up and squeeze blood back up to the heart when needed, such as when standing. In POTS syndrome, the sympathetic nerve supply to the lower limbs does not function properly and so there is pooling of blood in the lower extremities rather than being returned back up to the heart. This leads to dizziness on standing, known as orthostasis, and increase in heart rate, known as tachycardia. This is the most common form of POTS.
Hyperadrenergic basically means high adrenaline. Adrenaline and nor-adrenaline (epinephrine and nor-epinephrine) are natural stimulants within the body, the same ones released in the flight or fight response. Hyperadrenergic POTS patients have high levels of nor-epinephrine in their blood. As you can imagine these would lead to increasefd heart rate and blood pressure. In the more common neuropathic form of POTS, there is lower blood pressure and higher heart rate when standing. In hyperadrenergic POTS, there is often both increased blood pressure and heart rate when standing.
Secondary POTS refers to POTS syndrome that occurs as a result of another underlying condition that leads to damage of the nerves that usually control the redistribution of blood. These conditions include diabetes, lupus, alcoholism and chemotherapy. As part of the work up for POTS, a screening to rule out secondary causes is usually performed.