Pheo in pregnancy is very rare. Most people with pheo are diagnosed after they are 40. If they know they have pheo, younger women would have the tumor removed before becoming pregnant. When pheo does occur in pregnancy, it usually is a big surprise and can have serious consequences to the mother and the fetus. Pheo in pregnancy is one of those “cannot afford to miss” diseases. Once suspected, diagnosis and treatment are usually straightforward and the mother and fetus can expect great outcomes.
Pheo in pregnant women is usually subclinical before pregnancy. The metabolic changes during pregnancy and the growing uterus tend to make the tumor more active. In my experience, pheo-induced hypertension usually occurs later in pregnancy but it can occur much earlier. Clinically it is difficult to differentiate between preeclampsia and pheo. My suggestion to obstetricians is to have a low threshold to test pheo. If the blood pressure is hard to control or there are paroxysmal symptoms such as palpitation, sweating, and headache, I would test pheo just not to miss it. In the vast majority of pregnant women, the test results are negative and pheo is ruled out. In those with clearly elevated pheo markers (the markers are usually markedly elevated in pregnancy), abdominal MRI is then done and the pheo is usually in one of the adrenal glands. CT and MIBG scan are contraindicated in pregnancy due to the associated radiation to the fetus. If pheo is diagnosed in the 1st or 2nd trimester (< 24 weeks), the woman is treated with phenoxybenzamine and beta blocker for preoperative preparation and the tumor is resected laparoscopically. If pheo is diagnosed in the 3rd trimester, the woman is still treated with phenoxybenzamine and beta blocker. When fetus is mature enough, Cesarean section is done, followed by tumor resection.
As pheo in pregnancy is a dramatic disease, there are always a few case reports every year, each with a little different flavor in it. The conclusion of most cases is to consider pheo in a pregnant woman with unusual hypertension. The case brought up by reader DJPheo was about a 27-year-old woman. Biochemical diagnosis was very clear but initial abdominal MRI did not identify a tumor. She received a PET/CT scan which localized the tumor. As DJPheo points out, the case raised a few issues. First, it is surprising that the abdominal MRI did not identify the mass (which is sizable at 5.7 x 2.8 x 3.1 cm) adjacent to the spine. Second, what should be done next if the mass is not seen even by experienced radiologist on abdominal MRI? Most would recommend MRI of the pelvis, chest, and neck. Third, if no tumor is seen after MRI of neck and trunk, what should be done next? I would make sure the blood pressure is well controlled and wait until after delivery (probably safer by C-section) for MIBG scan or PET. At any rate, this case should not be construed as evidence supporting PET/CT scan for localizing pheo in pregnancy. Rather the moral is that you need to find a good radiologist to read the MRI images.
Dr. Pheo
Sunday, January 23, 2011
Tuesday, November 23, 2010
Corticosteroid and pheo
This interesting topic is suggested by a reader. The relationship between corticosteroid and pheo is multifold and involves several fundamental physiological issues.
Firs of all, the close proximity of the adrenal cortex and adrenal medulla is an intriguing phenomenon. The adrenal glands are small organs. An adrenal gland actually is further divided into two organs, the cortex (secreting corticosteroid) and medulla (where pheo is derived from), each with related but different functions. Why is the adrenal medulla wrapped around by the cortex? Why isn't the medulla located inside other organs, say, the spleen or liver, or a free-standing organ like a ganglion? I can only think of two other organs, pituitary and pancreas, which are also further divided into two organs. In the case of pituitary, anterior and posterior; pancreas, exocrine and endocrine. The question is still unsettled. Existing evidence suggests that the corticosteroid secreted by the adrenal cortex is important in maintaining the medulla what it is. If one takes the cells from the medulla and puts them in culture, those cells automatically differentiate into neuronal cells. If one adds high concentrations of corticosteroid into the culture, the medulla cells will remain neuroendocrine cells and do not differentiate into neuronal cells. As the medulla cells are derived from the neurocrest during embryonic development, it is hypothesized that the migrating neurocrest cells encounter adrenal cortex cells (which provide high concentrations of corticosteroid) and really like them and stay with them. Thus the story of adrenal cortex and adrenal medulla.
Second, corticosteroid stimulates catecholamine production and release from cultured adrenal medulla cells. Corticosteroid increases catecholamine production by upregulating the key enzymes for catecholamine production. The mechanisms for which corticosteroid stimulates catecholamine release are not clear and may not be straightforward.
Third, corticosteroid prepares the target tissues of catecholamines to be responsive to catecholamines. That is why patients with adrenal insufficiency often have low blood pressure even when they have high catecholamine levels.
Lastly, there have been a number of case reports on pheo crisis induced by corticosteroid use. The pheo crisis usually starts a few hours after corticosteroid use. There may be hemorrhage within the pheo. In patients with known pheo or an adrenal tumor of unclear nature, corticosteroid should be avoided if possible. When corticosteroid is used, patients should be closely monitored. In my own experience, pheo crisis by corticosteroid is rare and not a predictable event.
On a separate note, I have been very busy recently. To readers who are used to my quick responses, I may appear to become sloppy. I apologize. I am still following this blog closely but not as frequently as before. Please rest assured that I will respond to your questions, just not as timely.
Have a great Thanksgiving!
Dr. Pheo
Firs of all, the close proximity of the adrenal cortex and adrenal medulla is an intriguing phenomenon. The adrenal glands are small organs. An adrenal gland actually is further divided into two organs, the cortex (secreting corticosteroid) and medulla (where pheo is derived from), each with related but different functions. Why is the adrenal medulla wrapped around by the cortex? Why isn't the medulla located inside other organs, say, the spleen or liver, or a free-standing organ like a ganglion? I can only think of two other organs, pituitary and pancreas, which are also further divided into two organs. In the case of pituitary, anterior and posterior; pancreas, exocrine and endocrine. The question is still unsettled. Existing evidence suggests that the corticosteroid secreted by the adrenal cortex is important in maintaining the medulla what it is. If one takes the cells from the medulla and puts them in culture, those cells automatically differentiate into neuronal cells. If one adds high concentrations of corticosteroid into the culture, the medulla cells will remain neuroendocrine cells and do not differentiate into neuronal cells. As the medulla cells are derived from the neurocrest during embryonic development, it is hypothesized that the migrating neurocrest cells encounter adrenal cortex cells (which provide high concentrations of corticosteroid) and really like them and stay with them. Thus the story of adrenal cortex and adrenal medulla.
Second, corticosteroid stimulates catecholamine production and release from cultured adrenal medulla cells. Corticosteroid increases catecholamine production by upregulating the key enzymes for catecholamine production. The mechanisms for which corticosteroid stimulates catecholamine release are not clear and may not be straightforward.
Third, corticosteroid prepares the target tissues of catecholamines to be responsive to catecholamines. That is why patients with adrenal insufficiency often have low blood pressure even when they have high catecholamine levels.
Lastly, there have been a number of case reports on pheo crisis induced by corticosteroid use. The pheo crisis usually starts a few hours after corticosteroid use. There may be hemorrhage within the pheo. In patients with known pheo or an adrenal tumor of unclear nature, corticosteroid should be avoided if possible. When corticosteroid is used, patients should be closely monitored. In my own experience, pheo crisis by corticosteroid is rare and not a predictable event.
On a separate note, I have been very busy recently. To readers who are used to my quick responses, I may appear to become sloppy. I apologize. I am still following this blog closely but not as frequently as before. Please rest assured that I will respond to your questions, just not as timely.
Have a great Thanksgiving!
Dr. Pheo
Sunday, October 31, 2010
Report from NANETS meeting
I just returned from the NANETS meeting. Before the meeting, I had hoped that I would get to meet colleagues interested in pheo and see new studies on pheo at the NANETS meeting held in Santa Fe, October 29 and 30. NANETS stands for North American Neuroendocrine Tumor Society. It is a very nice society of doctors who treat neuroendocrine tumors. Pheo is a neuroendocrine tumor. Although the meeting was very informative on carcinoid and pancreatic endocrine tumors, there were literally only one study on pheo and one talk that mentioned pheo in passing.
The one study by a researcher in Dallas essentially showed that the mTOR pathway probably is not particularly important in the transformation from benign to malignant pheo and mTOR inhibitors (such as RAD001) probably won’t work for malignant pheo. The talk on modern gene testing by Dr. Marx at NIH briefly mentions the controversial issue of prenatal diagnosis of MEN2 (I had an earlier post on this topic in this blog) but did not delve further into pheo gene testing.
Dr. Pheo
The one study by a researcher in Dallas essentially showed that the mTOR pathway probably is not particularly important in the transformation from benign to malignant pheo and mTOR inhibitors (such as RAD001) probably won’t work for malignant pheo. The talk on modern gene testing by Dr. Marx at NIH briefly mentions the controversial issue of prenatal diagnosis of MEN2 (I had an earlier post on this topic in this blog) but did not delve further into pheo gene testing.
Dr. Pheo
Saturday, September 11, 2010
Coping with a frustrating disease
In an earlier post, I described my experience on alternative diagnosis for patients who have pheo symptoms but without pheo. Most patients cope with their conditions very well and go on with their lives. A small number of patients would see multiple physicians, get numerous tests and imaging studies, and try all kinds of medications, herbs, or behavioral therapies, just to get a definitive diagnosis and to get back to their "perfect" health. As a pheo specialist, I am often the doctor who tells them not only they don't have pheo but a clear diagnosis cannot be established. I explain that further diagnostic work-up is unlikely to yield a definitive diagnosis. I then discuss the skills of coping with a frustrating disease.
First of all, these patients do have a disease. And the disease is not their fault. They just simply have it and they have not done anything to make the disease afflict on them.
Second, medicine has its limits. In spite of the ever-growing progress in medicine, there are many things we don't know in medicine. Sometimes, a definitive diagnosis cannot be reached no matter how hard one may try. We have to wait for the disease to fully reveal itself over time.
Third, look at the brighter side. Although we don't know the diagnosis, we do know that it is not a bad one. It is not cancer, not heart disease, not a disease that will cost a limb or organ, and not deadly if the symptoms have been going on for many years.
Lastly, the most important issue is coping with the disease. What is the purpose of perfect health? What are the important things in life? Can one pursue the goals in life with the disease? What limits one from doing the desired things? The best approach is to focus on functionality rather than on perfect health. If one can do the things one wants to do, that's not too bad even with the disturbing symptoms mimicking pheo. I like to use a car metaphor. Most of us want to have fancy expensive cars but most of us cannot get those cars. If we keep lamenting on the lack of those cars, we lose the purpose of life. Those of us without fancy cars will get a car we can afford with the functions that we think are the most important. Then we drive the car to do the things we want to do. Simply owning a fancy car won't necessarily drive us somewhere.
Dr. Pheo
First of all, these patients do have a disease. And the disease is not their fault. They just simply have it and they have not done anything to make the disease afflict on them.
Second, medicine has its limits. In spite of the ever-growing progress in medicine, there are many things we don't know in medicine. Sometimes, a definitive diagnosis cannot be reached no matter how hard one may try. We have to wait for the disease to fully reveal itself over time.
Third, look at the brighter side. Although we don't know the diagnosis, we do know that it is not a bad one. It is not cancer, not heart disease, not a disease that will cost a limb or organ, and not deadly if the symptoms have been going on for many years.
Lastly, the most important issue is coping with the disease. What is the purpose of perfect health? What are the important things in life? Can one pursue the goals in life with the disease? What limits one from doing the desired things? The best approach is to focus on functionality rather than on perfect health. If one can do the things one wants to do, that's not too bad even with the disturbing symptoms mimicking pheo. I like to use a car metaphor. Most of us want to have fancy expensive cars but most of us cannot get those cars. If we keep lamenting on the lack of those cars, we lose the purpose of life. Those of us without fancy cars will get a car we can afford with the functions that we think are the most important. Then we drive the car to do the things we want to do. Simply owning a fancy car won't necessarily drive us somewhere.
Dr. Pheo
Friday, August 6, 2010
Should you see Dr. Pheo?
A few readers have expressed interest in seeing me for a formal consultation. I appreciate their encouragement. I do often see patients from other parts of the state or country. Seeing an outside expert has some pros and cons.
Pro 1. Definitive answer to specific questions. By the time you feel the need of seeing an outside expert, usually you already have done a lot of tests and imaging and received various opinions. The outside expert has the vantage position of reviewing all of the information and your natural clinical course. Of course the expert is also most experienced on some specific diseases. Whether the answer is yes, no, or further studies needed, you will have an answer.
Pro 2. Getting the best diagnostics and treatments. The outside expert usually works in an academic medical center and works closely with other experts. They can see things that were omitted before and usually do things “right”. Further diagnostic procedures and surgical operations are usually carried out by expert physicians as well.
Con 1. An expert is an expert on certain diseases but not on all diseases. Sometimes my patients are impressed by my knowledge on pheo and other neuroendocrine tumors and they assume that I know everything. I always explain that I do know a lot about pheo and other rare tumors and I am a good general endocrinologist as well, but my knowledge on other medical conditions is limited. Thus an expert can give you definitive answer to your specific question but she/he cannot solve all of your health problems.
Con 2. Follow-up is challenging. Patients and their diseases are ever-changing. For chronic and non-emergent questions, you can easily communicate with the expert by phone or email. For acute issues, it is important to ask a local physician who knows your condition well. Remember that the outside experts usually have responsibilities in research, teaching, and administration, besides clinical care. The expert may go to a scientific conference or vacation. All these make accessibility an issue.
Con 3. Extra cost and insurance coverage issues. These are self-explanatory.
Based on my experience, I believe there are some general rules-of-thumb on whether a patient should see an out-of-town specialist and how the patient can benefit the most from an outside expert. Here are my recommendations:
1. Find a local doctor who you trust and like and who has some basic knowledge on your condition. For pheo-related diseases, an endocrinologist or an internist is a good choice. This doctor has to be open-minded and comfortable at learning new knowledge.
2. Either ask the local doctor to identify an expert or find one yourself. Ask your doctor to contact the expert, explaining why the patient needs to see the expert and what specific questions need to be answered.
3. Before you go, send all doctor’s notes, lab results, CT/MRI and other imaging studies on CDs (not just the reports) to the expert.
4. When you are there, remember the specific questions your doctor and you want to ask the expert. Be realistic about what the expert can do (give definitive answers to specific questions) and cannot do (cure all ills). The expert may already have arranged additional diagnostics and possibly sessions with a surgeon or other experts so that you will have more efficient use of time there.
5. After you return, work closely with your local doctor and make sure that the local doctor and the expert communicate. Carry out the plan laid out by the expert and consult the expert on non-emergent questions. For emergency questions, you have to be lucky to be able to locate the expert all the time. Your local doctor is your best help.
What about seeing Dr. Pheo? All the rules apply. In addition, I will ask you to respect my wish to be anonymous as Dr. Pheo. Of course you will know my real name before you actually see me but please do not divulge Dr. Pheo’s identity publicly. I will post one of my email addresses later.
By the way, I will be on vacation from late August to Early September and may not have internet access during that time.
Dr. Pheo
Pro 1. Definitive answer to specific questions. By the time you feel the need of seeing an outside expert, usually you already have done a lot of tests and imaging and received various opinions. The outside expert has the vantage position of reviewing all of the information and your natural clinical course. Of course the expert is also most experienced on some specific diseases. Whether the answer is yes, no, or further studies needed, you will have an answer.
Pro 2. Getting the best diagnostics and treatments. The outside expert usually works in an academic medical center and works closely with other experts. They can see things that were omitted before and usually do things “right”. Further diagnostic procedures and surgical operations are usually carried out by expert physicians as well.
Con 1. An expert is an expert on certain diseases but not on all diseases. Sometimes my patients are impressed by my knowledge on pheo and other neuroendocrine tumors and they assume that I know everything. I always explain that I do know a lot about pheo and other rare tumors and I am a good general endocrinologist as well, but my knowledge on other medical conditions is limited. Thus an expert can give you definitive answer to your specific question but she/he cannot solve all of your health problems.
Con 2. Follow-up is challenging. Patients and their diseases are ever-changing. For chronic and non-emergent questions, you can easily communicate with the expert by phone or email. For acute issues, it is important to ask a local physician who knows your condition well. Remember that the outside experts usually have responsibilities in research, teaching, and administration, besides clinical care. The expert may go to a scientific conference or vacation. All these make accessibility an issue.
Con 3. Extra cost and insurance coverage issues. These are self-explanatory.
Based on my experience, I believe there are some general rules-of-thumb on whether a patient should see an out-of-town specialist and how the patient can benefit the most from an outside expert. Here are my recommendations:
1. Find a local doctor who you trust and like and who has some basic knowledge on your condition. For pheo-related diseases, an endocrinologist or an internist is a good choice. This doctor has to be open-minded and comfortable at learning new knowledge.
2. Either ask the local doctor to identify an expert or find one yourself. Ask your doctor to contact the expert, explaining why the patient needs to see the expert and what specific questions need to be answered.
3. Before you go, send all doctor’s notes, lab results, CT/MRI and other imaging studies on CDs (not just the reports) to the expert.
4. When you are there, remember the specific questions your doctor and you want to ask the expert. Be realistic about what the expert can do (give definitive answers to specific questions) and cannot do (cure all ills). The expert may already have arranged additional diagnostics and possibly sessions with a surgeon or other experts so that you will have more efficient use of time there.
5. After you return, work closely with your local doctor and make sure that the local doctor and the expert communicate. Carry out the plan laid out by the expert and consult the expert on non-emergent questions. For emergency questions, you have to be lucky to be able to locate the expert all the time. Your local doctor is your best help.
What about seeing Dr. Pheo? All the rules apply. In addition, I will ask you to respect my wish to be anonymous as Dr. Pheo. Of course you will know my real name before you actually see me but please do not divulge Dr. Pheo’s identity publicly. I will post one of my email addresses later.
By the way, I will be on vacation from late August to Early September and may not have internet access during that time.
Dr. Pheo
Wednesday, July 28, 2010
If not pheo, what do I have?
Pheo is a rare disease. In my practice, I see many patients who are suspected by their doctors of having pheo. After evaluating the patients, I generally find that only about 10% of them really have pheo, but the other 90% do not. The patients' response is usually predictable. Those who are diagnosed by me to have pheo are happy (and apprehensive, of course) after I discuss the nature of the disease and treatment plan. Those who do not have pheo are disappointed and frustrated. From the patients' point of view, they don’t care too much whether they have pheo or not per se, but they do want to feel better. If it is not pheo, what else is wrong?
About half of the patients for whom pheo is ruled out, especially young patients with hypertension, just have “essential hypertension”. Essential hypertension is a vague diagnosis simply meaning that the doctors don’t know why the patients have hypertension. Most patients with essential hypertension have a family history of hypertension. Their hypertension has multiple causes but none of the causes stands out obviously.
About a quarter of patients have obstructive sleep apnea (OSA). Patients with OSA are in a chronic stress mode so that they have catecholamine surges. OSA is pretty common and affects 5-10% of all people. Many people do not know they have OSA. The doctor has to probe whether the patient snores or has daytime somnolence. If the patient has suggestive symptoms, a consultation from a sleep specialist or pulmonologist is very valuable. The effects of CPAP treatment can be dramatic.
Another quarter of patients have anxiety disorder. People tend to have negative emotional reactions toward anxiety disorder. Some would wonder why they have the disease if they are not really anxious about anything. Anxiety disorder is a disease that we don’t know the cause of, just as depression is a disease that we don’t know the cause of. Patients should be evaluated by a psychiatrist to make the anxiety disorder diagnosis and to provide treatment.
There are nearly 30 other diseases that can also mimic pheo. These are generally much rarer and I do not see them often. Finally, I want to emphasize that the above is based on my personal experience; other doctors may have a different view.
Dr. Pheo
About half of the patients for whom pheo is ruled out, especially young patients with hypertension, just have “essential hypertension”. Essential hypertension is a vague diagnosis simply meaning that the doctors don’t know why the patients have hypertension. Most patients with essential hypertension have a family history of hypertension. Their hypertension has multiple causes but none of the causes stands out obviously.
About a quarter of patients have obstructive sleep apnea (OSA). Patients with OSA are in a chronic stress mode so that they have catecholamine surges. OSA is pretty common and affects 5-10% of all people. Many people do not know they have OSA. The doctor has to probe whether the patient snores or has daytime somnolence. If the patient has suggestive symptoms, a consultation from a sleep specialist or pulmonologist is very valuable. The effects of CPAP treatment can be dramatic.
Another quarter of patients have anxiety disorder. People tend to have negative emotional reactions toward anxiety disorder. Some would wonder why they have the disease if they are not really anxious about anything. Anxiety disorder is a disease that we don’t know the cause of, just as depression is a disease that we don’t know the cause of. Patients should be evaluated by a psychiatrist to make the anxiety disorder diagnosis and to provide treatment.
There are nearly 30 other diseases that can also mimic pheo. These are generally much rarer and I do not see them often. Finally, I want to emphasize that the above is based on my personal experience; other doctors may have a different view.
Dr. Pheo
Thursday, June 17, 2010
Is MIBG scan still needed?
MIBG is a chemical that has similar structure to that of catecholamines. Radioiodine-labeled MIBG is taken up by both normal adrenal medulla and pheo. Because pheo is usually much larger than the adrenal medulla, if one exists, it tends to light up with MIBG much more than normal adrenal medulla.
When MIBG scan began to be used clinically in the 1980s, CT and MRI were not yet available in clinical care. Initial clinical studies indeed showed that the MIBG scan was a great test, boasting a sensitivity of 90% (meaning that if there is a pheo, the chance that it will be shown is 90%) and a specificity of 95-100% (meaning that if you don’t have a pheo, the chance that no signal will be shown is 95-100%). The very high specificity was especially appealing to those clinicians who had little experience on pheo. Pheo is a disease nobody wants to miss. So, the reasoning goes, if MIBG scan result is negative, pheo can be ruled out.
Since the 1980s, better biochemical tests have become available and CT and MRI household names. Of course the new tests and CT and MRI have their own problems but every patient suspected to have pheo get those. Should the patient also get an MIBG scan? Will the MIB scan provide new information on whether the patient has pheo in the first place, or if she/he has pheo, how many and where they are?
In this month, two papers with opposite views appear respectively in Journal of Clinical Endocrinology and Metabolism and Endocrine Practice, the former being the world’s leading endocrinology journal, the latter a smaller journal with a readership of mostly American practicing endocrinologists. The first paper is an analysis of 15 clinical studies on MIBG using iodine 123. The conclusion is that MIBG scan has a sensitivity of 94% and specificity of 92%. The authors of this paper believe that their paper “supports the continued utility of I-123 MIBG imaging in the diagnosis and management of patients with pheochromocytoma.”
The second paper is a retrospective clinical study of MIBG scan (both I-131 and I-123) in a large US hospital in the last 14 years. There are quite a few interesting findings in this paper. First, MIBG scan is not really indicated in 76% of patients (in other words, three quarters of modern-day MIBG scans are wasted). Second, the sensitivity and specificity are both only about 70%. Lastly, the most important finding is that the MIBG scan does not provide any new information after biochemical testing and CT or MRI. Even worse, about 35% of the MIBG scans provide misleading information (i.e. showing adrenal uptake but patient does have pheo or no uptake but patient has pheo). The authors of this paper conclude that MIBG scan “is not necessary for most patients in modern practice.”
Why do these two papers have opposite conclusions on the MIBG scan? Like everything else, the devil is in the details. The 15 studies analyzed in the first paper are all well-controlled clinical studies performed by expert clinicians. They use very stringent and clearly defined criteria to call the MIBG scan result positive or negative. As matter of fact, borderline adrenal uptake is considered a negative result. In the second paper, the MIBG scan is ordered by clinicians with various experience on pheo. Borderline adrenal uptake is considered positive result. The authors’ rationale is that most clinicians and patients treat any adrenal uptake as alarming, which I do agree with. If borderline uptake is considered negative, the sensitivity and specificity increase to about 90%. Even that, the MIBG scan still does not provide useful new information. The first paper unfortunately does not address the utility of MIBG scan after biochemical testing and CT or MRI. Besides the second paper, a couple of other papers in the last few years also fail to show that MIBG scan has any clinical utility.
What do I do? My own experience is that MIBG scan seldom helps. I do order it in the following patients who I already diagnose as having pheo: young patients (<50-year-old), patients with family history or mutations, patients with previous pheo, and patients with multiple pheo, patients who have adrenal masses on both sides, and patients in whom CT/MRI does not find the pheo. Those patients are rare, though.
Dr. Pheo
When MIBG scan began to be used clinically in the 1980s, CT and MRI were not yet available in clinical care. Initial clinical studies indeed showed that the MIBG scan was a great test, boasting a sensitivity of 90% (meaning that if there is a pheo, the chance that it will be shown is 90%) and a specificity of 95-100% (meaning that if you don’t have a pheo, the chance that no signal will be shown is 95-100%). The very high specificity was especially appealing to those clinicians who had little experience on pheo. Pheo is a disease nobody wants to miss. So, the reasoning goes, if MIBG scan result is negative, pheo can be ruled out.
Since the 1980s, better biochemical tests have become available and CT and MRI household names. Of course the new tests and CT and MRI have their own problems but every patient suspected to have pheo get those. Should the patient also get an MIBG scan? Will the MIB scan provide new information on whether the patient has pheo in the first place, or if she/he has pheo, how many and where they are?
In this month, two papers with opposite views appear respectively in Journal of Clinical Endocrinology and Metabolism and Endocrine Practice, the former being the world’s leading endocrinology journal, the latter a smaller journal with a readership of mostly American practicing endocrinologists. The first paper is an analysis of 15 clinical studies on MIBG using iodine 123. The conclusion is that MIBG scan has a sensitivity of 94% and specificity of 92%. The authors of this paper believe that their paper “supports the continued utility of I-123 MIBG imaging in the diagnosis and management of patients with pheochromocytoma.”
The second paper is a retrospective clinical study of MIBG scan (both I-131 and I-123) in a large US hospital in the last 14 years. There are quite a few interesting findings in this paper. First, MIBG scan is not really indicated in 76% of patients (in other words, three quarters of modern-day MIBG scans are wasted). Second, the sensitivity and specificity are both only about 70%. Lastly, the most important finding is that the MIBG scan does not provide any new information after biochemical testing and CT or MRI. Even worse, about 35% of the MIBG scans provide misleading information (i.e. showing adrenal uptake but patient does have pheo or no uptake but patient has pheo). The authors of this paper conclude that MIBG scan “is not necessary for most patients in modern practice.”
Why do these two papers have opposite conclusions on the MIBG scan? Like everything else, the devil is in the details. The 15 studies analyzed in the first paper are all well-controlled clinical studies performed by expert clinicians. They use very stringent and clearly defined criteria to call the MIBG scan result positive or negative. As matter of fact, borderline adrenal uptake is considered a negative result. In the second paper, the MIBG scan is ordered by clinicians with various experience on pheo. Borderline adrenal uptake is considered positive result. The authors’ rationale is that most clinicians and patients treat any adrenal uptake as alarming, which I do agree with. If borderline uptake is considered negative, the sensitivity and specificity increase to about 90%. Even that, the MIBG scan still does not provide useful new information. The first paper unfortunately does not address the utility of MIBG scan after biochemical testing and CT or MRI. Besides the second paper, a couple of other papers in the last few years also fail to show that MIBG scan has any clinical utility.
What do I do? My own experience is that MIBG scan seldom helps. I do order it in the following patients who I already diagnose as having pheo: young patients (<50-year-old), patients with family history or mutations, patients with previous pheo, and patients with multiple pheo, patients who have adrenal masses on both sides, and patients in whom CT/MRI does not find the pheo. Those patients are rare, though.
Dr. Pheo
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