Pelvic Venous Disease, POTS, and MCAS

You have been told the pelvic pain is normal. That the low back ache is postural. That the heaviness in your legs is from standing too long. That the veins that have surfaced on your legs, or your vulva, are cosmetic. That the pressure you feel after eating, after sitting, after a long day on your feet is just how your body works now.

You have probably seen a gynecologist, a neurologist, a gastroenterologist, maybe a urologist. Each one found something, or found nothing, and sent you on your way.

What almost none of them checked was your veins.

Pelvic venous disease is chronically underdiagnosed. Not because it’s hard to see. Because nobody thinks to look.

Three Diagnoses, One Overlooked Category

Pelvic congestion syndrome, May-Thurner syndrome, and Nutcracker Syndrome are distinct conditions that share a common thread: blood that cannot flow the way it should.

In pelvic congestion syndrome, the ovarian and pelvic veins become enlarged and incompetent, functioning like varicose veins deep inside the body. Blood pools in the pelvis instead of returning efficiently to the heart. What patients describe is a dull, heavy, chronic pelvic ache that builds as the day goes on, intensifies around menstruation, and is aggravated by prolonged standing, sitting, or physical activity. Intercourse is often painful, and characteristically the pain doesn’t stop when intercourse does and often settles into a deep ache that lasts for hours afterward, sometimes into the next day.

In May-Thurner syndrome, the right common iliac artery crosses over and compresses the left common iliac vein, restricting venous outflow from the left leg and pelvis. Left-sided predominance is a useful clue when it’s there with swelling, heaviness, and aching worse on the left, or a visible size difference between the legs. But plenty of my patients have symptoms on both sides, and I don’t use symmetry to rule the diagnosis out. Once outflow is obstructed, blood finds another way, and the collateral networks it recruits run across the midline through the pelvis. Symptoms follow those collaterals. What patients describe is leg tightness that gets worse throughout the day, and varicose veins on the left leg, or both, that may have been treated previously but came back because the problem was never in the vein that was treated. Varicose veins can also appear on the vulva and labia. Some develop spider veins and skin changes: darkening, thickening, occasionally ulceration. And in some patients the first sign is a deep vein thrombosis (DVT), attributed to the pill, a flight, or bad luck for years before anyone asks why it happened where it did.

In nutcracker syndrome, the left renal vein is caught between the aorta and the superior mesenteric artery, like a nut in a cracker. The compression backs pressure up into the left kidney and, critically, into the left ovarian or testicular vein, which drains directly into it. That single anatomic fact explains most of what these patients feel. The classic finding is left flank pain. What patients actually describe is often more diffuse than that: back pain that generalizes rather than staying over the kidney, abdominal pain, bloating and early satiety that have usually been worked up as IBS or gastroparesis, and pelvic pain, heaviness, dyspareunia, painful periods, varicosities of the vulva or thigh. In men, testicular aching and a left varicocele, which is typically treated as the problem rather than read as a sign of one. Symptoms tend to worsen with standing, activity, and spinal extension, and ease with lying down. Right-sided pain is common enough to mention, and it is the finding that most often derails the diagnosis: the lesion is on the left, so right-sided symptoms get read as evidence against it. They aren’t. Once again, this is likely due to collateral flow. Blood in the urine is the textbook finding, but in my experience, it is less consistently present.

These three conditions are not rare. They are overlooked. And in my practice, they almost never arrive in isolation.

A Pattern Worth Recognizing

Everything described so far is a problem of blood that can’t get out of the pelvis. If that’s true, the consequences shouldn’t stop at the pelvis, and they don’t. The most consistent one I see is orthostatic intolerance, and in a substantial number of these patients it has already been named: POTS (Postural Orthostatic Tachycardia Syndrome).

The presentation is familiar. A woman comes to me because she can’t stand for more than a few minutes without feeling like she could faint. Her heart pounds when she gets up. She has brain fog, crushing fatigue, headaches that are worse upright and better lying down, and a body that feels like it’s constantly fighting itself. Showers are exhausting. Grocery stores are exhausting. She has been told it’s anxiety or deconditioning. These symptoms are consistent with postural orthostatic tachycardia syndrome (POTS) and it is one of the more common ways venous compressions announce itself.

Orthostatic Intolerance is generally approached as a primary disorder of the autonomic nervous system. When I look further in these patients, I often find Pelvic Venous Compressions upstream of the nervous system entirely. Sometimes May-Thurner. Sometimes nutcracker. Sometimes both.

The connection isn’t subtle once you see it. The pelvic and abdominal veins hold a major share of circulating blood volume. When they’re compressed or incompetent, blood pools in the lower body on standing instead of returning to the heart. Cardiac filling drops. The heart compensates by racing. Cerebral perfusion falls with it, which is where the fog, the fatigue, and the upright headache come from. The autonomic nervous system, sensing the imbalance, shifts into chronic activation. That is POTS. But the nervous system isn’t malfunctioning here but rather it’s compensating, accurately, for blood that isn’t coming back. In a subset of these patients, the problem was mechanical the whole time.

Compression Is Not the Beginning of the Story

This is where the standard narrative stops. Treat the compression, improve the symptoms, done. I don’t think that’s the whole story. And the evidence from my patient population suggests it isn’t. The majority of my patients with pelvic venous disease also have underlying mast cell activation syndrome or MCAS. Not as a coincidence. As a pattern that repeats too consistently to ignore.

Mast cells are immune cells stationed throughout the body, concentrated at every interface between your internal environment and the outside world. They line the gut, the skin, the airways, the nerves — and every blood vessel in the body. Every single one.

When mast cells function properly, they are first responders: releasing chemical signals that fight infection, heal wounds, and coordinate immune responses. When they become chronically dysregulated, releasing their mediators too easily in response to triggers that shouldn’t register as threats, they become a source of sustained, systemic inflammation.

That’s mast cell activation syndrome, and I think it’s considerably more common than most physicians recognize. Conservative estimates put it at 17 percent of the population. In my clinical experience, particularly since the pandemic, the true number is likely higher.

What Mast Cells Are Doing to Your Veins

Mast cells are embedded in vessel walls, positioned to monitor and respond to everything flowing through them. When they activate chronically, the consequences for vascular integrity are significant. They release enzymes such as elastase, chymase, and matrix metalloproteinases such as MMP-9 that degrade the structural proteins holding vessel walls together. Collagen and elastin, the materials that give veins their shape and resilience, break down. Vessels become more compliant, less able to resist the pressures that cause them to dilate and pool. Histamine contributes to vasodilation and increases vascular permeability, making vessel walls leakier. Fluid shifts into surrounding tissue, which likely accounts for some of the edema and swelling these patients describe in their legs and lower abdomen.

That explains a vein that stretches. It doesn’t explain a vein that gets crushed and this is where the third piece comes in. Hypermobile Ehlers-Danlos syndrome, POTS, and MCAS travel together often enough that the association has a name in the literature: the triad. Most of my patients with pelvic venous disease have at least two of the three, and many have all three. It’s usually presented as a puzzling clinical association. I’d argue that the interaction between mast cells and connective tissue explains a good deal of it.

Connective tissue does more than hold joints together. It holds the abdominal organs in place. When it’s lax, they sit lower than they should, and the spaces vessels pass through get tighter. Compression syndromes are markedly overrepresented in hypermobile patients, and that isn’t a coincidence. The anatomy that produces compression is, in part, a connective tissue phenotype.

So, the triad stops looking like three conditions that happen to co-occur. Impaired connective tissue creates the compression. The compression causes venous pooling, which causes POTS. And mast cells sit at both ends, degrading the matrix that holds vessels open, and the matrix that holds vessels apart, while the resulting inflammation feeds back on all of it.

Mast cells release heparin locally, thinning the blood right where they sit. The enzymes they release simultaneously degrade the connective tissue supporting nearby capillaries and small vessels, which leak more readily as a result. Leakier vessels, thinner blood and together they account for the bruising these patients describe, which usually appears with no injury behind it.

Why Treating the Compression Isn’t Always Enough

Stenting works, and that deserves saying plainly. When a genuine obstruction is relieved in the right patient, the response can be striking; leg heaviness and pelvic pain resolve, exercise tolerance returns, and orthostatic symptoms improve in ways no medication for POTS or MCAS had touched. Some of these patients get their lives back. For a woman who has spent years being told her symptoms were anxiety, watching her heart rate stabilize after a mechanical problem is corrected is not a small thing.

But not every patient gets the whole way there, and the pattern in those who don’t is consistent enough to be informative. What wasn’t treated is the inflammatory environment that predated the structural problem, contributed to it, and in many cases outlasts it. The mast cells are still dysregulated. The mediators are still circulating. The autonomic nervous system is still sensitized. The nerve-immune loop that chronic inflammation establishes is still running. Mast cells exciting nearby nerves, those nerves signaling back to the mast cells, the cycle sustaining itself independent of any identifiable trigger.

And the conditions that travel with MCAS don’t resolve on their own either. The connective tissue that allowed the compression to develop is unchanged. The mediator-driven reactivity is unchanged. Where mast cell disease has driven gastrointestinal symptoms, urinary symptoms, or dysautonomia beyond the venous contribution, those persist — because a stent addresses one mechanism in a patient who has several.

Structural intervention gives the body an opportunity to heal. It doesn’t give the body what it needs to take that opportunity. That’s what mast cell–targeted therapy is for.

One Compression Rarely Travels Alone

There is something important I have learned from years of evaluating these patients: when you find one compression, look for others.

A patient who is tall and thin and has lost significant weight needs evaluation not just for nutcracker syndrome but for MALS (median arcuate ligament syndrome), where the diaphragm compresses the celiac artery and for SMAS (superior mesenteric artery syndrome), where the angle between the aorta and the superior mesenteric artery narrows enough to compress the duodenum.

My first referral for anyone I suspect has a compression syndrome is an interventional radiologist with specific interest in this area. They are the ones positioned to order the right imaging whether ultrasound, Doppler studies, MRV and to interpret it with the clinical context these patients require. They are the ones who will ultimately determine whether stenting, conservative management, or further workup is appropriate. But they are not always easy to find. And in the meantime, the patient in front of me still needs care. Which means I start the workup with what I have- ultrasound, orthostatic testing, a thorough clinical history and then I refer when I can, while treating what I’m already seeing.

The Hormonal Piece

Pelvic venous disease is overwhelmingly a condition of women in their reproductive years. That’s not accidental but it’s worth being precise about what it explains. Hormones account for the skew, not for the disease. Men have the same anatomy, the same venous physiology, and often the same underlying mast cell disease and they get venous compression. What they lack is the amplifier.

Estrogen promotes venous dilation and reduces the tone of vein walls. Where venous return is already compromised, this compounds the problem substantially. In pregnancy, blood volume rises dramatically and estrogen surges, triggering the development or worsening of pelvic venous disease.

Mast cells carry estrogen receptors, and estrogen can directly promote degranulation. So, at the points in the cycle when estrogen is highest, mast cells are more readily triggered, and inflammatory signaling in and around the pelvic veins is correspondingly more active. Progesterone withdrawal in the days before menstruation opens a second window, which is why so many of these patients describe symptoms that worsen at two distinct points in the month rather than one.

The perimenstrual flare isn’t only the mechanical pressure of a congested pelvis. It’s a hormonally timed immune event occurring in tissue that’s already inflamed.

It may also help explain why so many of these patients have endometriosis or adenomyosis alongside pelvic venous disease. Rather than separate misfortunes, these may be conditions that share an estrogen-sensitive, mast cell–mediated inflammatory mechanism and cluster in the same patients because they share an upstream driver.

In men, the hormonal amplifier is absent. The mast cell component isn’t. Male patients with iliac vein compression or nutcracker syndrome and underlying MCAS show the same vascular fragility, the same disproportionate reactivity, the same autonomic involvement without the monthly rhythm that makes the pattern recognizable in women. The immune mechanism is the constant; the hormonal environment determines how visibly it cycles. Which is part of why men wait longer for the diagnosis: the cyclical pattern is one of the strongest clues, and in men there isn’t one.

What Actually Helps

The goal of treatment is not to pick between structural intervention and immune modulation. It is both, in the right sequence, with the right monitoring. Address the compression. This is not optional for patients with confirmed venous outflow obstruction. Stenting of May-Thurner syndrome, embolization for pelvic congestion syndrome, and appropriate evaluation of nutcracker and other compression syndromes should be pursued with specialists experienced in these conditions. For many patients, structural treatment produces meaningful improvement in POTS, pain, and quality of life that nothing else will replicate.

Treat the mast cells. H1 and H2 antihistamines used together lower the histamine load and reduce baseline mast cell reactivity. Mast cell stabilizers like cromolyn, ketotifen, and natural options like quercetin and luteolin quiet the release of the broader mediator profile. Low-dose naltrexone modulates immune function and addresses the pain sensitization that chronic inflammation creates. These are not cures. They are tools for lowering the inflammatory baseline that everything else sits on top of. There are many other options as well.

Consider GLP-1 receptor agonists

GLP-1 receptors are expressed directly on mast cells, as well as on immune cells, gut nerves, and vascular endothelium. Engaging those receptors quiets inflammatory signaling through a mechanism entirely independent of appetite or weight. In a case series published in July 2025 by our group in the American Journal of the Medical Sciences, 89 percent of highly treatment-resistant MCAS patients showed meaningful clinical improvement, including systemic, neurologic, gastrointestinal, and skin symptoms, at doses well below those used for weight loss. This is not a medication to begin casually. It requires slow titration, close monitoring, and a physician who understands both GLP-1 therapy and mast cell disease. In the right patient, the results can be profound.

Consider Therapeutic Plasma Exchange

For patients with severe, treatment-resistant disease, plasmapheresis removes the plasma itself, along with the circulating mediators and cytokines it carries, lowering the inflammatory burden in a way that medication doesn’t replicate. While there are no trials to point to here, only case reports and clinical experience, I include it because for the patients who have exhausted everything else, I’ve seen responses I can’t otherwise account for. Patients who hadn’t responded to anything in years have improved across multiple systems after a series of treatments and held that improvement. It isn’t first line. For the patients who need it, it can be what finally moves them forward.

What to Ask Your Medical Provider

Chronic pelvic pain. Aching legs. Leg swelling or enlarged veins. Abdominal Pain. Symptoms that worsen with prolonged standing. POTS. Reactions to foods and medications. A body that flares without explanation. If that pattern fits you, these are the questions worth bringing to your physician:

• Has anyone evaluated me for pelvic venous compression? Not just pelvic congestion syndrome broadly but specifically May-Thurner and nutcracker syndrome as well.
• Has anyone checked my iron? Not just hemoglobin but specifically ferritin, TIBC, and iron saturation. Nutcracker syndrome can cause blood loss that leads to iron deficiency, and iron deficiency itself worsens mast cell activation.
• Has anyone evaluated me for MCAS? Not allergy testing, but mast cell mediator testing, collected and handled correctly with samples kept cold and processed without delay. Under the consensus-2 criteria, two elevated mediators alongside a consistent multisystem clinical history and response to mast cell–targeted therapy establish the diagnosis.

If the answer to any of those is no, you have somewhere to start.

The Vein Nobody Checked

Pelvic venous disease has spent decades framed two ways that limit it. As a structural problem that resolves once the anatomy is corrected. And as a condition that belongs to women.

Both framings have helped some patients. They’ve left others partially treated, still symptomatic, still being told the imaging looks fine so they must be fine. And they’ve left a group of men undiagnosed altogether, because no one thought the category applied to them.

Imaging shows the compression. It doesn’t show the inflammatory environment that preceded it, sustains it, and continues after it’s treated. It doesn’t show the mast cells embedded in the vessel walls, the lax connective tissue that let the compression develop, the autonomic dysfunction, the nerve sensitization, or the systemic mediator load that explains why these patients feel the way they do well beyond the pelvis.  Structural disease and immune disease aren’t competing explanations. They’re in the same patient, seen from different angles.

The vein nobody checked was always part of a larger story.

Dr. Tania Dempsey is a physician at the AIM Center for Personalized Medicine specializing in complex chronic illness, mast cell activation syndrome, and multisystem inflammatory disease.

Key references:

Afrin LB, Weinstock LB, Dempsey TT, Aschenbrenner K, Blitshteyn S, Schofield JR. Utility of glucagon-like-peptide-1-receptor agonists in mast cell activation syndrome. Am J Med Sci.2025;370(4):377-382.

Afrin LB, Ackerley MB, Bluestein LS, Brewer JH, Brook JB, Buchanan AD, Cuni JR, Davey WP, Dempsey TT, et al. Diagnosis of mast cell activation syndrome: a global “consensus-2”. Diagnosis (Berl). 2020 Apr 22;8(2):137-152. doi: 10.1515/dx-2020-0005. PMID: 32324159.