Adrenal medullary hyperplasia (AMH) is a rare condition in which the inner core of the adrenal gland, the medulla, grows abnormally thick and overproduces stress hormones called catecholamines. Because those hormones are the same ones released by a pheochromocytoma, the two conditions look almost identical on lab tests and on the exam table, but the treatment decisions and long-term outlook can differ in ways that matter. A 2023 systematic review pooling every published case found only 66 patients in the entire medical literature, which gives you a sense of how uncommon and how poorly understood this diagnosis remains.
What AMH Looks Like Clinically
The symptoms of AMH are driven by the same catecholamine surge that defines pheochromocytoma. In the systematic review, roughly nine out of ten patients showed signs of catecholamine excess. The most common presentation was high blood pressure, found in about three-quarters of patients. Nearly one in five of those with hypertension experienced it in sudden spells rather than as a constant elevation. Other frequent complaints included palpitations in about 45% of patients, excessive sweating in roughly a third, headaches in 30%, and anxiety in about 15%.1The Journal of Clinical Endocrinology & Metabolism. Adrenal Medullary Hyperplasia: A Systematic Review and Meta-analysis – Section: Results
If that list sounds exactly like a classic pheochromocytoma description, that is the core diagnostic problem with AMH. The clinical presentation alone cannot separate the two. Even the biochemistry overlaps heavily: elevated catecholamines were detected in 86% of AMH patients, whether measured in the urine or in the blood. The difference tends to be one of degree, not kind. A study comparing the two conditions directly found that noradrenaline and metanephrine levels were generally lower in AMH than in pheochromocytoma, and the adrenal glands suppressed less on a dexamethasone suppression test.2PubMed Central. Presentation, Treatment, Histology, and Outcomes in Adrenal Medullary Hyperplasia Compared With Pheochromocytoma – Section: Results Still, those differences are averages across groups. For an individual patient in a clinic, the overlap is too large to rely on blood tests alone.
The Diagnostic Challenge
AMH presents a genuine catch-22 for clinicians. The condition is defined pathologically, meaning you need tissue under a microscope to confirm it. The original diagnostic criteria proposed in 1980 require a combination of clinical symptoms suggesting pheochromocytoma, elevated urinary catecholamines, diffuse expansion of the medulla into the outer wings of the gland, and a demonstrably increased ratio of medulla to cortex measured by careful tissue analysis.3PubMed. Adrenal medullary hyperplasia: a clinicopathologic study of four cases In other words, you cannot be sure the diagnosis is AMH until after surgery has already been performed and a pathologist has weighed and sliced the gland.
Imaging helps to varying degrees. CT scans picked up an enlarged adrenal gland or an adrenal mass in only about 46% of patients. MIBG scintigraphy, a nuclear scan that lights up catecholamine-producing tissue, showed abnormal uptake in roughly 39%. Ultrasound was normal in the vast majority of cases, around 94%, making it essentially useless for this diagnosis. MRI, when performed, tended to show adrenal growth, but very few patients had one.4The Journal of Clinical Endocrinology & Metabolism. Adrenal Medullary Hyperplasia: A Systematic Review and Meta-analysis – Section: Results This inconsistency across imaging modalities has been openly acknowledged in the literature: a Chinese case series of 12 patients noted that while their own workups relied heavily on CT, MRI, and ultrasound, the effectiveness of these technologies for AMH remains debated.5PubMed Central. Diagnosis and Treatment of Adrenal Medullary Hyperplasia: Experience from 12 Cases – Section: Discussion
Practically speaking, AMH is often an accidental finding. About a quarter of AMH patients in one series were never even suspected of having the condition before surgery. They went to the operating room for a presumed adrenocortical adenoma or another adrenal mass, and the pathology report came back showing medullary hyperplasia instead.6PubMed Central. Presentation, Treatment, Histology, and Outcomes in Adrenal Medullary Hyperplasia Compared With Pheochromocytoma – Section: Results
Who Gets AMH
In the systematic review, the median age at diagnosis was 48 years, and close to 60% of patients were male. About seven in ten cases were sporadic, meaning they occurred without an identifiable inherited syndrome. The remaining roughly 23% were linked to multiple endocrine neoplasia type 2 (MEN2), a hereditary cancer syndrome caused by mutations in the RET gene. Most patients, about 73%, had disease in only one adrenal gland.7The Journal of Clinical Endocrinology & Metabolism. Adrenal Medullary Hyperplasia: A Systematic Review and Meta-analysis – Section: Results
Sporadic AMH is genuinely puzzling. Without a known genetic driver, the cause in most of these patients remains unexplained. Occasional case reports describe sporadic bilateral disease with all the hallmarks of pheochromocytoma: hypertension, biochemical abnormalities, and relief after surgical removal.8PubMed. Sporadic bilateral adrenal medullary hyperplasia: apparent false positive MIBG scan and expected MRI findings But these individual cases do little to reveal why the medulla overgrows when no inherited mutation is present.
The MEN2 Connection and the Micro-Pheochromocytoma Debate
The relationship between AMH and MEN2 is where the science gets genuinely provocative. In patients with MEN2, AMH has long been considered a precursor stage, a stepping stone on the way to developing a full pheochromocytoma. A molecular study tested this idea directly by comparing the genetic fingerprints of AMH tissue and pheochromocytoma tissue from the same MEN2 patients. The researchers found identical patterns of genetic damage in both. Loss of genetic material at several chromosome regions occurred at similar rates in AMH and in the frank tumors.9PubMed Central. Adrenal medullary hyperplasia is a precursor lesion for pheochromocytoma in MEN2 syndrome
That finding led the study authors to a bold proposal: AMH in MEN2 is not really hyperplasia at all. It already carries the molecular hallmarks of a tumor. They suggested replacing the term “adrenal medullary hyperplasia” in MEN2 patients with “micro-pheochromocytoma” for any adrenal medullary growth under one centimeter. The practical implication is that clinicians should not treat AMH in MEN2 patients as something less serious than pheochromocytoma. If the DNA damage is already there, the distinction between an overgrown gland and a tiny tumor becomes academic.
This renaming proposal has not been universally adopted, but it reflects a genuine shift in how the condition is understood in the hereditary setting. A mouse model of MEN2B, created by introducing the corresponding RET mutation, showed that chromaffin cell hyperplasia progressed to pheochromocytoma over time, offering experimental support for the precursor-to-tumor pathway.10PubMed Central. C-cell hyperplasia, pheochromocytoma and sympathoadrenal malformation in a mouse model of multiple endocrine neoplasia type 2B
Beyond RET Mutations
RET is not the only gene implicated. A case report documented bilateral AMH in a patient carrying a germline mutation in the MAX gene, which encodes a protein involved in cell growth regulation. In that patient, the MAX protein was absent from the hyperplastic medullary tissue, whether the overgrowth was diffuse or nodular. This finding suggested that the MAX mutation alone was sufficient to drive medullary overgrowth and that nodular AMH in this genetic context, much like in MEN2, should be considered a micro-pheochromocytoma rather than simple hyperplasia.11PubMed Central. Pathological and genetic characterization of bilateral adrenomedullary hyperplasia in a patient with germline MAX mutation – Section: Discussion
The broader lesson from these genetic findings is that the category “adrenal medullary hyperplasia” may be hiding several different diseases under one label. In MEN2, it appears to be an early-stage tumor. In MAX mutation carriers, something similar seems to be happening. In the majority of sporadic cases, the underlying biology remains unclear. Whether those sporadic cases follow the same precursor-to-tumor sequence or represent a fundamentally different process is an open question the current evidence cannot answer.
Concurrent Tumors Are Common
One surprising detail from the systematic review is how often AMH shows up alongside other tumors. More than half of the 66 patients had a concurrent tumor of some kind. Among those patients with coexisting neoplasms, pheochromocytoma was found in about 42%, medullary thyroid cancer in roughly 24%, and adrenocortical adenoma in about 29%.12The Journal of Clinical Endocrinology & Metabolism. Adrenal Medullary Hyperplasia: A Systematic Review and Meta-analysis – Section: Results The high overlap with pheochromocytoma underscores how blurry the boundary is between AMH and frank tumor, especially in hereditary cases. The presence of medullary thyroid cancer in nearly a quarter of those with concurrent tumors reflects the MEN2 subset, since medullary thyroid cancer is another hallmark of that syndrome.
For clinicians, this means that finding AMH on a pathology report should trigger a careful search for associated conditions, especially if the patient has not already been screened for MEN2 or other hereditary tumor syndromes. A patient diagnosed with AMH who also has medullary thyroid cancer almost certainly warrants RET gene testing.
Treatment and What Happens After Surgery
The primary treatment for symptomatic AMH is surgical removal of the affected adrenal gland. In the systematic review, 88% of patients underwent adrenalectomy, and about three-quarters of those who had surgery achieved resolution of their symptoms.13The Journal of Clinical Endocrinology & Metabolism. Adrenal Medullary Hyperplasia: A Systematic Review and Meta-analysis – Section: Results That is a reassuring success rate, though not perfect.
Preparation for surgery matters. Because catecholamine-producing tissue can trigger dangerous blood pressure swings during an operation, patients with pheochromocytoma are routinely given alpha-blocker medications beforehand to stabilize their cardiovascular system. The same approach is used for AMH patients, generally at lower doses and for shorter periods than for classic pheochromocytoma. However, because AMH is often not suspected before surgery, about a quarter of AMH patients in one series went to the operating room without alpha-blocker pretreatment. In that study, the untreated patients all turned out to have AMH without a coexisting pheochromocytoma, and their surgeries were performed for a different presumed diagnosis, typically an adrenal cortical tumor.14PubMed Central. Presentation, Treatment, Histology, and Outcomes in Adrenal Medullary Hyperplasia Compared With Pheochromocytoma – Section: Results
Long-term follow-up data for AMH are remarkably thin. The systematic review noted that essentially no long-term outcome data existed across the published literature, with the exception of a single patient who experienced recurrent symptoms eight months after surgery, possibly due to hyperplasia in the other adrenal gland.15The Journal of Clinical Endocrinology & Metabolism. Adrenal Medullary Hyperplasia: A Systematic Review and Meta-analysis – Section: Results The comparison study of AMH and pheochromocytoma patients, which tracked outcomes over an average of about 11 years, found that roughly a third of AMH patients eventually developed a new pheochromocytoma, and 11% died during follow-up. No metastatic pheochromocytoma developed in the AMH group, a meaningful distinction from pheochromocytoma patients, where metastasis occurred in 5%.16PubMed Central. Presentation, Treatment, Histology, and Outcomes in Adrenal Medullary Hyperplasia Compared With Pheochromocytoma – Section: Results
That one-third recurrence rate is clinically important. It means AMH patients are not simply cured by one surgery and sent home. They need ongoing surveillance, particularly if a hereditary syndrome is involved.
A Condition Recognized Relatively Recently
AMH was not recognized as a clinical entity until the early 1960s. A 1962 report in JAMA described what the authors called the first documented case: a patient with all the signs and symptoms of pheochromocytoma, positive on every standard diagnostic test, who was found at surgery to have medullary hyperplasia rather than a tumor. After removal of the gland, symptoms resolved and the previously abnormal test results normalized. The authors recommended that when surgical exploration for a suspected pheochromocytoma finds no tumor, bilateral biopsies of the medulla should be performed to check for hyperplasia.17JAMA. Hyperplasia of the Adrenal Medulla: A Clinical Entity
Sixty years later, that recommendation still captures the essence of the diagnostic dilemma. AMH is often found only because a surgeon went looking for a pheochromocytoma and did not find one. The condition has remained in the shadows partly because of its rarity and partly because confirming it requires tissue that can only be obtained by removing the gland.
Environmental Triggers and Animal Research
Most discussions of AMH focus on genetics, but environmental stress can also drive medullary growth, at least in animal models. A study exposing rats to simulated high-altitude conditions (equivalent to roughly 5,500 meters) for 28 days found a marked increase in adrenal gland weight caused by hyperplasia of both the cortex and the medulla. The researchers attributed the medullary overgrowth to the body’s sustained need for extra catecholamines in a low-oxygen environment.18PubMed. Adrenal corticomedullary hyperplasia in hypobaric hypoxia
Whether chronic hypoxia or other physiological stressors contribute to sporadic AMH in humans is unknown. People living at extreme altitudes or those with chronic respiratory conditions that keep oxygen levels low have not been systematically studied for medullary changes. The animal data raise the possibility, but bridging that gap to clinical practice would require the kind of large-scale studies that a condition this rare is unlikely to attract.
Quality of Life After Adrenal Disease
Patients who undergo adrenalectomy for AMH often want to know what their life will look like afterward. Disease-specific data for AMH barely exist, but broader research on quality of life across adrenal diseases offers some perspective. A systematic review of quality-of-life studies found that patients with adrenal conditions, whether caused by hormone overproduction or underproduction, tended to report reduced quality of life compared with healthy individuals. Treatment generally improved outcomes but did not fully restore quality of life to normal levels, even when blood tests showed that hormone levels had returned to the expected range.19PubMed. Quality of life in patients with adrenal disease: A systematic review This finding is relevant for AMH patients who achieve symptom resolution after surgery but continue to feel that something is off. The disconnect between normalized lab values and persistent subjective symptoms is well documented across adrenal conditions and is worth discussing with a clinician rather than dismissing.
For AMH patients with bilateral disease or those who require removal of both adrenal glands, the stakes are higher. Losing all adrenal tissue means lifelong dependence on hormone replacement, including cortisol and sometimes mineralocorticoids. This is another reason why the question of whether to operate on both sides or to take a watch-and-wait approach on a second gland is not straightforward, particularly in hereditary cases where bilateral involvement is expected to develop over time.