VAQ 4 Answer

This was a real case, the main presenting complaint was severe pleuritic chest pain, and before we even got the CTPA, the lab called with the FBE result… An unpleasant surprise, for us and the patient. Turns out the patient had a pulmonary embolus as his presenting sign of his acute leukaemia.

This is a tricky question, as you need to address all of the parameters in the FBE, and tie it in with the clinical information provided.  There are only a few differential diagnoses, but unless you’re thinking laterally you may not pick them.

As per all path answers, lets tackle it from the top.

As a time saver you can try and “double up” so you comment on 2 or 3 parameters at a time. Also, this result lends itself to a “spot diagnosis” summary at the start, although you could leave it til the end:

Acute leukaemia with evidence of bone marrow impairment (anaemia & thrombocytopenia).

(We put the “likely” in as you’ll see, there’s a couple of differentials).

Hb 76, MCV 110: Moderate macrocytic anaemia.
  Consistent with increased RBC turnover)
(remember immature RBC’s or reticulocytes are larger than mature RBC)
Given other parameters:
Likely acute leukaemia
DDx in setting of moderate thrombocytopenia
B12/Folate defic/Thyroid/Liver disease  =  less likely

Moderate thrombocytopenia: again – likely BM failure
DDx:    Clumping/sampling error
           Increased consumption: ITP/TTP/HUS/DIC
Bleeding risk not significantly increased

And here’s the money:
Marked leukocytosis with neutropenia & >20% blasts = Bone marrow infiltrative disorder:
Most Likely Dx: acute leukaemia
High promyelocytes: possible acute promyelocytic leukaemia
DDx for high WCC:
   Other myleoproliferative/dysplastic disorder
   Secondary BM infiltration by solid tumor
Moderate to severe neutropenia – at risk for bacterial infection

And don’t forget to comment on the normals…
Lymphocytes – normal (hard to know what to say about this…) ? ALL less likely

Increased nucleated RBC (NRBC): consistent with increased bone marrow turnover

NB: Other Ix may help clarify Dx:
Urgent blood film
    Sepsis: expect left shift/toxic granulation
    TTP/HUS: expect fragmented RBC/retics/hemolysis
DIC screen: coags, fibrinogen D-dimer
Inflammatory markers (ESR, CRP)

FBE showing likely acute leukaemia, clinical signs suggest possible pulmonary embolus = Haematologic emergency

I’d probably crack on and attack the clinical information now, to try & tie it all together…

NB: In afebrile patient with:
  Unilateral pleuritic chest pain
  Mild hypotension
Pulmonary embolus: CTPA (if Cr OK), or V/Q if renal impairment
   NB: D-Dimer has NO ROLE in PE Dx in the case
Pneumonia: CxR
Consider other less likely DDx:
   Ischemia: ECG, troponin
   Dissection: will see on CTPA

(NB Another rare cause of chest pain leukaemic patients is Thymic infiltration and enlargement… Anyone put that down?!)

Management will include:
A/B/C: O2 aim sats > 94%, IV access, fluids, analgesia
Further Rx depends on Dx of chest pain
   Eg anticoagulation, ABx
Urgent Haematology referral
Needs admission for BM aspirate to confirm Dx
  BM aspirate for: morphology, immunophenotyping and cytogenetics

And lastly… (I hear the pitter patter of little bunny feet, here come some “fluffy bunnies”)
…this isn’t really a question about “breaking bad news” but you’d be mad to not mention something akin to:

Explain of Dx to patient
Address chest pain Dx and incidental haem findings
Ensure family/significant other in attendance
Guarded prognosis pending Haem r/v & BM aspirate
Social work support prn
Notify patients GP

So there you go, one of the most common investigations we order, the humble FBE, can sometimes yield startling results, and you need to know what to do when you get a result like this.  Remember it’s not always leukaemia, so consider the differentials, and remember the fluffy bunnies, as telling a patient they have not one, but two potentially fatal conditions is a shocking piece of news to break.

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