A 36 year old cattle farmer was admitted to hospital with a flu like illness. 3 days after admission he developed arthralgia and progressive shortness of breath. There was a soft systolic murmur over the precordium. Chest X-Ray showed bilateral infiltrates.

ECG showed non-specific ST-T changes. Troponin raised. Echo revealed decreased LV function.
Hb 90 G/L, reticulocytes 4%.

List 5 differential diagnoses for his presentation.

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College Answer

1.  Viral pneumonia
2.  Legionella
3.  Pneumococcal
4.  Q fever
5.  Mycoplasma
6.  Infective endocarditis
7.  Vasculitis (unlikely)

Discussion

This is a pneumonia with bone marrow suppression, myocarditis (or pericarditis) and possibly some sort of connective tissue involvement. What could it be?

A list of differentials would include the following:

Those last two were suggested by a contributor, who ventured that they may be legitimate responses to the question. You don't get that impression that malaria or sickle cell disease are causing this picture from the history, but - does the biochemistry/haematology fit? Anaemia and reticulocytosis is all you get there. Anaemia and reticulocytosis could certainly be from malaria or sickle cell disease, but they could also be from a hundred other causes, so you'd not want to base your answer on those two findings solely. You could try to fit malaria in there because of the flu-like illness story (because that implies fevers). You could probably make this look like sickle cell more easily (spin the ST changes Xray changes and arthralgias into a sickle cell crisis). But, why the whole "cattle farmer" back story? And where is the jaundice you'd get with malaria and sickle cell disease?

But then, you look at what the college wrote in their answer. They've got a bunch of stuff in there which has no relationship with anaemia and reticulocytosis at any level. "Pneumococcal", they say. Mycoplasma.  In short, malaria and sickle cell disease are just as plausible as the college "model" differentials. 

Anyway, the links in the list presented above follow to the paper which describes cardiovascular involvement from that pathogen. However, one cannot rule out the idea that this patient has pulmonary oedema due to an acute mitral insufficiency due to infective endocarditis from some other agent.

 

References

Rajiv, C., et al. "Cardiovascular involvement in leptospirosis." Indian heart journal 48.6 (1995): 691-694.

Bowles, Neil E., et al. "Detection of viruses in myocardial tissues by polymerase chain reactionevidence of adenovirus as a common cause of myocarditis in children and adults." Journal of the American College of Cardiology 42.3 (2003): 466-472.

Nelson, D. P., et al. "Cardiac legionellosis." CHEST Journal 86.6 (1984): 807-808.

Wilson, H. G., et al. "Q fever endocarditis in Queensland." Circulation 53.4 (1976): 680-684.

SANDS, MILTON J., et al. "Pericarditis and perimyocarditis associated with active Mycoplasma pneumoniae infection." Annals of internal medicine 86.5 (1977): 544-548.

Aronin, Steven I., et al. "Review of pneumococcal endocarditis in adults in the penicillin era." Clinical Infectious Diseases 26.1 (1998): 165-171.\

Bax, H. I., et al. "Brucellosis, an uncommon and frequently delayed diagnosis."Neth J Med 65.9 (2007): 352-355.