Gail,
That's an interesting article about H. POTS. I have a few additions and thoughts about your posts.
Levels of mediators, including histamine, can bounce around a lot for a variety of reasons. If a person isn't producing too much or one's mast cells aren't releasing too much histamine, e.g., that person could be ingesting it from foods that are high in histamine. Almost any food can contain a high level of histamine, as it's a product of deterioration, although certain foods more commonly contain large amounts, even when fresh. Other foods cause direct histamine release, so that would also temporarily raise a histamine level and potentially cause symptoms.
If histamine isn't the cause of symptoms, then it's possible there isn't a MC disorder involved in the illness, or the person might be super-sensitive to small amounts, as others have said. Even if histamine isn't an issue, there are a number of vasodilators that can produce flushing and other symptoms similar to a MCA disorder, as well as other diseases.
I would not go off my H1 antihistamines, as I believe they help me feel better, even though my histamine level has been low, and I have been diagnosed with SM. Some antihistamines, such as desloratidine (Clarinex), also have a stabilizing effect on mast cells, so help reduce degranulation and release of a number of mediators, as stated in this abstract. Desloratidine specifically stabilizes mast cells in the skin:
[url]http://www.ncbi.nlm.nih.gov/pubmed/19826448/url]
Regarding diagnosis of Pheochromocytoma, this article seems to be more detailed and more current (2012) than the article you cited. If it doesn't answer your specific question, re-post what it is you want to know.
http://ssl.texmed.org/virtual/cme/PDF/12DIA_30.pdfIt's not, though, written specifically for a differential diagnosis of H. POTS or MCAD. Still it's always surprising how testing changes in such a short time! This article includes a list of meds that should be discontinued for a period of time before testing, including clonidine.
To be clear, pheochromocytoma is one of several diseases that need to be ruled out before a MCAD is ruled in. Symptoms such as flushing, tachycardia, and others are found in several diseases, as well as in reactions to high histamine foods. In some diseases, antihistamines are helpful, so testing must be used to differentiate among the possibilities.
Gail, thanks for putting in the original references. That's helpful when people are trying to put questions into perspective. Often we have to go back to the research someone is reading to figure out a question or answer.
While we all have somewhat different symptoms, and those don't necessarily reflect the seriousness of the illness, my opinion is that medicating should be done in conjunction with a mast cell expert. They are knowledgeable about testing and possible differential diagnoses. They have a great deal more experience in prescribing and adjusting meds to fit the individual's symptoms and type of MC disorder. They also are aware of interactions of meds, co-existing conditions that can interfere with treatment, and other facts that will help to keep patients safer and more comfortable. For example, using epinephrine to control a carcinoid syndrome crisis can kill the patient, yet it can be life-saving for a MC patient.
Finally, it's not uncommon for MC patients to have variable BP depending on symptoms. Mine is routinely low (90-100/60). Yet, on at least 2 occasions, during anaphylactic episodes, my BP went very high. This presents a dilemma for ED doctors when we come in with high BP, no breathing difficulty, and ask for epinephrine. That's one reason why guidelines for treatment and a letter from a doctor can be helpful. Epi is what brought my BP down and stopped the anaphylaxis for me very quickly. Before I was diagnosed, I would wake up every morning with 80/50 BP. A combination of meds, hydration, etc. helped raise my a.m. BP.
If you haven't already done so, I would recommend seeing a mast cell disorder specialist for a full work-up and diagnosis.