MTB vs. MAI

[delicatefade]

OK, so I'm reading Rapid Review Path again. On pg 188, Goljan says that the most common cause of TB in AIDS patients is MAI. I thought to myself, how can that possibly be true??? I know that MAI infections are much more prevalent in the HIV/AIDS population, especially as the CD4 count drops below 50, but surely MTB is still the most common cause of TB, right???

If you had a question like this and both MTB and MAI were possible as answers, what would you put??? Would you really put MAI if MTB was also a possible answer??? Would the presence of a CD4 count in the stem of the question make a difference???

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[AmoryBlaine]

uhhh... that's wrong.

MAI doesn't cause Tb under any circumstances. That's like saying "the most common cause of Chlamydia is N. gonnorhaea."

Like the way my mind went straight for the gutter on that one?

 

[delicatefade]

I realize it sounds like an idiotic statement.

I'm guessing what he meant was perhaps "the most common cause of a TB-like disease in HIV/AIDS is MAI"...

 

[turkdlit]

I realize it sounds like an idiotic statement.

I'm guessing what he meant was perhaps "the most common cause of a TB-like disease in HIV/AIDS is MAI"...

When I heard this in the lecture, I assumed he meant the most common cause of a mycobacterium infection in HIV patients is MAI...which coincidentally is clinically indistinguishable from M. Tb

 

[OSUdoc08]

uhhh... that's wrong.

MAI doesn't cause Tb under any circumstances. That's like saying "the most common cause of Chlamydia is N. gonnorhaea."

Like the way my mind went straight for the gutter on that one?

Disseminated TB in an AIDS patient is caused by MAI.

TB isn't only caused by the organism with the same name.

Meningitis isn't just caused by organisms that end in "meningitidis." It is also caused by H. influenzae, L. monocytogenes, etc.

You can do the same thing with pneumonia. Is pneumonia only caused by organisms that end in "pneumoniae?" No.

 

[OSUdoc08]

OK, so I'm reading Rapid Review Path again. On pg 188, Goljan says that the most common cause of TB in AIDS patients is MAI. I thought to myself, how can that possibly be true??? I know that MAI infections are much more prevalent in the HIV/AIDS population, especially as the CD4 count drops below 50, but surely MTB is still the most common cause of TB, right???

If you had a question like this and both MTB and MAI were possible as answers, what would you put??? Would you really put MAI if MTB was also a possible answer??? Would the presence of a CD4 count in the stem of the question make a difference???

CD4 count <75 + disseminated TB = MAI

CD4 count >75 + TB = MTB

MTB & MAI both cause TB infections

 

[BlackNDecker]

Disseminated TB in an AIDS patient is caused by MAI.

TB isn't only caused by the organism with the same name.

I think you might be incorrect...

I think it's correct to say that TB is TB and MAI is MAI, whereas disseminated TB is miliary TB. I think this is why TB is on the differential for MAI, and vice versa.

Milliary TB

TB

MAI

 

[deleted9493]

My understanding is that both Mycobacteria cause virtually identical disease processes but in different populations, as noted by OSUdoc. Miliary TB is merely a disseminated stage of either disease process.

I really think that that page in Goljan is correct. Remember, AIDS patients are defined by a CD4 of less than 200 and HIV virus and you've alread said that MTB show up in a big way at CD4 of less than 50...

 

[delicatefade]

Here's what my micro professor has to say about this:

MAI most often causes a disseminated disease (which can include) the lungs but the pateint manifests with diffuse intersitital infiltrates not consolidation with abscesses because of a lack of T cells.



But MAI disseminated disease is just that, diseemianted, if it was a pneumonia it would be called that. For example , the best specimen to confirm MAI infection in an AIDS patient is a bone amrrow biopsy, not a bronchioaviolar lavage.



The question is realy flawed because only MTB cause TB. The question should ask, which is the more common cause of pulmonary disease in an AIDS patient. Than I think TB is correct, but I would need to look it up.



The Most common opportunistic infections in advanced HIV/AIDS patients after P. jiroveci, are CMV, M. avium complex and cryptococsis.



The most common causes of CNS infection in advanced HIV/AIDS patients after HIV are Toxoplasmosis and Cryptococcosis.



Because of the fact that MAI disseminated infection is much more common in AIDS patients than MTB is (even with reactivation TB), the answer MAI is the best answer to a bad question.



Hope this helps!

 

[delicatefade]

Disseminated TB in an AIDS patient is caused by MAI.

That doesn't make any sense. If you were an attending in a hospital and your AIDS patient had a disseminated MAI infection, I bet you would NOT put disseminated TB in the chart.

What my professor said makes sense. Both MTB and MAI can obviously cause pulmonary infections, but MAI would be characterized more by diffuse infiltrates than consolidation. MTB would be more characterized by consolidation, UNLESS the CD4 count is really low, at which point MAI is probably more likely than MTB anyway.

 

[OSUdoc08]

That doesn't make any sense. If you were an attending in a hospital and your AIDS patient had a disseminated MAI infection, I bet you would NOT put disseminated TB in the chart.

What my professor said makes sense. Both MTB and MAI can obviously cause pulmonary infections, but MAI would be characterized more by diffuse infiltrates than consolidation. MTB would be more characterized by consolidation, UNLESS the CD4 count is really low, at which point MAI is probably more likely than MTB anyway.

If a newborn had meningitis, and the mother ate alot of feta cheese when she was pregnant, would you put your diagnosis in the chart as "meningitis" or "Listeria monocytogenes infection?"

I would put meningitis secondary to Listeria monocytogenes.

Just like I would put disseminated TB secondary to MAI.

 

[OSUdoc08]

I think you might be incorrect...

I think it's correct to say that TB is TB and MAI is MAI, whereas disseminated TB is miliary TB. I think this is why TB is on the differential for MAI, and vice versa.

Milliary TB

TB

MAI

I'm going with Goljan. You go with your emedicine.

I'm sticking with my pneumonia and meningitis examples.

 

[delicatefade]

If a newborn had meningitis, and the mother ate alot of feta cheese when she was pregnant, would you put your diagnosis in the chart as "meningitis" or "Listeria monocytogenes infection?"

I would put meningitis secondary to Listeria monocytogenes.

Just like I would put disseminated TB secondary to MAI.

Well that's fine as long as you didn't just put disseminated TB without the clarification that it is secondary to MAI. I still think it would be rather misleading to simply put disseminated TB without any additional information. I also think it would be more accurate to simply put disseminated MAI.

We're probably just nitpicking at this point....

 

[OSUdoc08]

Well that's fine as long as you didn't just put disseminated TB without the clarification that it is secondary to MAI. I still think it would be rather misleading to simply put disseminated TB without any additional information.

EXACTLY, just like it would be misleading to put "meningitis" or "pneumonia" without the name of the organism.