What’s up folks! I’m Dr. Zeb, back with another video from our New York office,
so I'll do my best to keep the background noise to a minimum.
The board-style question we’re reviewing today requires us to know how to diagnose a subtype
of pneumonia and its most likely cause. Click on the question link in the top
corner so you can follow along. And actually, I’d really appreciate it if you click on
any of the links you find useful as it helps in determining if these videos are beneficial to you.
I’d even recommend pausing here and first try to answer the question.
Once you’ve done that, let's start by determining what we should do by reading the lead-in.
“Which of the following is the most likely causal organism?”
Okay, we need to have a hypothesis of the diagnosis. Let’s see if the
diagnostic findings “An x-ray of the chest ray is shown.” can help us.
In the x-ray, we can see there are bilateral opacities that are predominantly distributed
in the upper lobes and include linear and nodular infiltrates as well as some confluency.
While this finding is still somewhat broad, what are some differentials we should be considering?
Definitely infectious, including atypical pneumonia or tuberculosis,
some pneumoconioses like silicosis, or possibly other inflammatory conditions like sarcoidosis.
Let’s start reading from the top to narrow down our diagnosis.
“A 39-year-old woman comes to the physician because of a fever,
nausea, and a nonproductive cough for 7 days.”
Ok, with this combination, I’m already leaning towards an infectious cause, and the hallmark
symptom of “nonproductive cough” is making me think immediately of atypical pneumonia,
sometimes called walking pneumonia because patients still walk about and conduct everyday
activities rather than stay at home and rest, which is more typical in typical pneumonia.
So reading on: “During this period, she has had headaches, generalized fatigue,
and muscle and joint pain. She has also had increasing shortness of breath for 2 days”
Okay, the constitutional symptoms and dyspnea are also aligned with our hypothesis,
and to save time, I’m going to jump to the vitals,
examination, and labs to look for more concrete findings.
“Her temperature is 38.1 degrees Farhenheit (mistake)” So a low-grade
fever, which also fits atypical pneumonia.
Let’s skip now to “The lungs are clear to auscultation.”
This is also consistent with atypical pneumonia.
“There are multiple skin lesions with a blue livid center, pale intermediate zone,
and a dark red peripheral rim on the upper and lower extremities.” Alright, this is a very
specific finding - the question writers only put such specific info in a vignette if it's a strong
pertinent positive for the correct answer. You can learn more about pertinent positives and negatives
in this question walkthrough. To me, this sounds very much like erythema multiforme.
As for labs, I’m mainly interested in a few things:
inflammatory findings link leukocytes or inflammatory markers like CRP or procalcitonin,
and possibly hemoglobin and sodium. Why hemoglobin?
Hemolytic anemia is associated with Mycoplasma pneumoniae, the most common cause of atypical
pneumonia - but more on that later. And why sodium?
Right, because another cause of atypical pneumonia, Legionella pneumophila,
often causes hyponatremia. So these readings may come in handy for ruling a pathogen in or out.
Alright, leukocytes are “11,100/mm3”
so still normal - but this is not unusual for atypical pneumonia.
And both hemoglobin and sodium are normal.
With all of the supporting findings,
I feel quite confident in going with atypical pneumonia as the most likely diagnosis.
But before we proceed to answer the question, I’d like to briefly consider:
Why not typical pneumonia? Well, many of the clinical features are,
of course, different from atypical and include: high fever and shaking chills,
productive cough with purulent sputum, decreased breath sounds and crackles on examination,
and on x-ray, lobar consolidation and alveolar pattern. Also, the pathogens
are typically extracellular bacteria rather than the intracellular pathogens common in atypical.
Hey typical, I got a joke for you.
What?
Why can’t you hear a patient with pneumonia urinate?
Uh…. I don't know.
Because the P is silent.
You can read more about these important differences in the Pneumonia AMBOSS article.
So with that in mind, what are the top 3 bacteria that cause this condition?
We already got a hint with intracellular… That’s right:
Mycoplasma pneumoniae (which we mentioned, is most common, especially in individuals
younger than 40), Chlamydophila pneumoniae, and Legionella pneumophila.
There are, of course, several others including Chlamydia psittaci transferred from birds,
Q fever due to Coxiella burnetii transferred from livestock,
and viruses, which are all less common. To help you remember bacterial causes,
remember the mnemonic: “Atypically, Legions of Clams Mind their P’s and Q’s”
With that in mind, let’s try to answer the question:
We see that both Mycoplasma and Legionella are
possible options. So how do we decide between the two?
Well, everything here fits Mycoplasma. So that passes with flying colors as a “most likely.”
Now what about Legionella? While the presenting symptoms could fit,
Legionella is an exception regarding fever, since it often causes temperatures greater than
39°C or 102.2°F. It’s also associated with exposure to contaminated water,
such as at an air-conditioned resort, cruise ship, or hospital and is often accompanied
by diarrhea as well as hyponatremia and its manifestations like confusion.
On your exam, a question about Legionella, which you’re likely to get, will give you a combination
of these supporting findings. In addition, chest X-ray findings are variable, but often show patchy
unilateral and lobar infiltrates that progress to consolidation rather than a diffuse interstitial
infiltrate. Lastly, Legionella pneumonia is not associated with erythema multiforme.
With that explanation, Mycoplasma pneumoniae is the most likely cause.
And now most importantly, what’s Mycoplasma’s favorite piece of art?
Pneumonia Lisa
Let’s briefly skim over the other options to see what high-yield concepts we can reinforce.
Klebsiella pneumoniae causes hospital-acquired pneumonia,
aspiration pneumonia, or, less commonly, community-acquired typical pneumonia in older men,
especially those with diabetes, chronic lung disease, or alcohol use disorder.
It would usually manifest with high fever and productive cough with thick and bloody sputum,
classically described as currant jelly. An x-ray would typically show consolidation in
an upper lobe with air bronchograms and possible bulging of an adjacent interlobar fissure.
Streptococcus pneumoniae is the most common cause of community-acquired typical pneumonia.
And we already covered why this is unlikely.
Haemophilus influenzae also causes typical pneumonia and more commonly affects children.
Staphylococcus aureus is a common cause of hospital-acquired pneumonia and often develops
as a superinfection in patients with influenza pneumonia. Although Staph. aureus pneumonia can
be associated with interstitial or patchy infiltrates on chest x-ray, this diagnosis
is unlikely because it usually occurs in the elderly or patients with immunodeficiency,
and this patient does not have a history of recent hospital admission.
With the explanations behind us, let’s consider what other questions we could get for this topic.
The question writers could have swapped Mycoplasma out for Chlamydophila pneumoniae
or they might have added a history of owning a parrot or other bird to make
Chlamydia psittaci a likely cause. The same goes for Coxiella burnetii and dealing with livestock.
They might have just asked for the diagnosis of atypical pneumonia.
Although more likely to appear in Step 1, perhaps they would have changed the options
to fitting microbiological findings, such as Mycoplasma growing on Eaton
agar or colorless Gram-staining due to lacking a cell wall.
They might have mentioned or asked about additional associations of Mycoplasma pneumoniae,
such as the formation of cold agglutinins (IgM)
or resulting subclinical hemolytic anemia, although this patient did have normal hemoglobin.
Lastly, they could have asked for the best antibiotic therapy, which would have been?
Right! Macrolides, fluoroquinolones, or tetracyclines
You can review all of this info in the AMBOSS library.
To summarize, the key concepts of this question are:
Diagnose atypical pneumonia based on common findings of nonproductive cough,
dyspnea, low-grade fever, unremarkable auscultation and labs,
and interstitial bilateral infiltrates on x-ray.
Know the causes of atypical pneumonia and their specific associations,
including mycoplasma pneumoniae as the most common, which can also cause erythema multiforme.
And that’s it for this question! If you found this video helpful, I’d really appreciate a thumbs up,
comment, or subscribe so I know to keep making them. Also, check out any of the question
link and social media channels in the description for even more content.
As always, remember that hard work pays off, so keep up the studying. You’ve got this.
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How much background noise can we get in one recording? Jeez...