Postural Orthostatic Tachycardia Syndrome, or POTS, is a condition involving the autonomic nervous system that causes a rapid heart rate increase upon standing. Within this syndrome, there are different types, including neuropathic POTS. This specific form is distinguished by damage to the small nerve fibers responsible for signaling blood vessels to constrict.
The Neuropathic Mechanism of POTS
Neuropathic POTS arises from small fiber neuropathy. This condition involves damage to the small autonomic nerve fibers that control blood vessel constriction. In individuals with this condition, these nerves do not function correctly, especially in the lower body.
When a person stands up, gravity pulls blood downward. A healthy nervous system responds by signaling the blood vessels in the legs and abdomen to tighten, which pushes blood back up to the heart and brain. In neuropathic POTS, the damaged small fiber nerves fail to send these signals effectively, resulting in blood pooling in the lower extremities and reducing the amount of blood returning to the heart.
The heart, sensing this reduced blood flow, compensates by beating faster to maintain circulation to the brain and other organs. This compensatory tachycardia is the defining feature of POTS. The underlying nerve damage can stem from various sources, such as autoimmune disorders that attack nerve fibers. Other potential triggers include viral infections, surgeries, or trauma.
Distinctive Symptoms and Presentation
While all forms of POTS share the hallmark symptom of a heart rate increase of 30 beats per minute or more upon standing, the neuropathic subtype often presents with additional symptoms related to nerve dysfunction. A common sign is a change in sweating patterns.
Individuals may experience reduced sweating, known as anhidrosis, particularly on their feet and legs. This occurs because the damaged small nerves also control sweat glands. This impairment can lead to significant heat intolerance, as the body is less able to cool itself effectively. The dysfunction in blood flow regulation also causes visible changes in the skin.
Many individuals with neuropathic POTS experience acrocyanosis, a condition where the feet and lower legs turn a reddish or bluish color when standing due to blood pooling. This discoloration is often accompanied by a cold sensation in the affected limbs. Beyond these signs, patients might also report sensory nerve symptoms such as tingling, burning, or numbness in their extremities.
Diagnostic Process for Neuropathic POTS
Confirming a diagnosis of neuropathic POTS involves a multi-step process that first establishes the presence of POTS and then identifies the specific neuropathic cause. The initial step is a Tilt Table Test, the standard for diagnosing POTS. During this test, a person is strapped to a table that is slowly tilted upright, while their heart rate and blood pressure are continuously monitored to observe the characteristic spike in heart rate.
Once POTS is confirmed, further testing is needed to pinpoint the neuropathic component. One such test is the Quantitative Sudomotor Axon Reflex Test (QSART). This procedure measures the function of the nerves that control sweating by stimulating the sweat glands and analyzing the volume of sweat produced. A reduced sweat response, especially in the lower limbs, can indicate small fiber neuropathy.
A more direct method for confirming nerve damage is a skin biopsy. This involves taking a very small sample of skin, typically from the ankle or thigh, to be examined under a microscope. A pathologist analyzes the sample to determine the density of the small nerve fibers within the skin. A lower-than-normal density of these fibers provides direct evidence of small fiber neuropathy.
Targeted Treatment Approaches
Treatment for neuropathic POTS is multifaceted, addressing both the general symptoms of orthostatic intolerance and the specific underlying nerve damage. Foundational strategies for all POTS patients include increasing fluid and salt intake to boost blood volume and wearing compression garments on the lower body to help prevent blood pooling.
Specific medications are often used to target the faulty mechanisms in neuropathic POTS. Midodrine is a medication that works by causing blood vessels to constrict, which helps to counteract the effects of nerve damage and improve blood return to the heart. Another option is pyridostigmine, which enhances the signaling between nerves, potentially improving the function of the compromised autonomic nerves.
When an underlying autoimmune cause is suspected or confirmed, treatments may focus on modulating the immune system. Therapies such as Intravenous Immunoglobulin (IVIG), which consists of concentrated antibodies from healthy donors, may be used to help calm the autoimmune attack on the nerves. Other immunosuppressive medications might also be considered to address the root cause of the nerve damage.