A 63-year old white woman with end-stage renal disease secondary to long-standing hypertension on unscheduled dialysis, atrial fibrillation on warfarin, and hyperlipidemia presents with a painful, ulcerated lesion with purpuric borders, surrounding retiform purpura, and central eschar. Biopsy demonstrated calcifications of small and mediam sized arteries with necrosis of the subcutaneous fat.
What is the likely diagnosis?
A forty-three year old white man with a history of untreated hepatitis C presents to urgent care clinic complaining of a pruritic rash on his wrist.
What is the diagnosis?
On Mondays, we post our image challenge of the week. Per popular demand, the answers will now be posted on the same day as the challenge.
On Mondays, we post our image challenge of the week. Look out for the answers on Friday of that same week.
Case: A 45-year old African-American woman presents to establish primary care. She is naive to the medical system. She complains of a 2-year history of gradually enlarging papules on her nose, cheek, forehead, and around her eyes (representative image shown below – image is not of the patient described here). They are violaceous, non-pruritic, non-photosensitive, and indurated. Her only other complaint is mild progressive dyspnea on exertion. Chest X-ray demonstrates hilar lymphadenopathy.
Question: What is the finding shown above? For which disease is it specific? Tune in Friday for the answer!
For spuriously found thrombocytopenia, consider pseudothrombocytopenia, which is an in vitro phenomenon characterized by platelet aggregation and does not have hemostatic consequence. If suspected, collect a blood sample in a citrate-buffered tube (“blue-top” tube) normally used for coagulation testing. In pseudothrombocytopenia, this maneuver will usually prevent platelet aggregation and result in a normal platelet count.
Pseudothrombocytopenia is an in vitro phenomenon. It results from EDTA-dependent platelet aggregation and the inability of platelet counters to count clumped platelets accurately. EDTA is a common anticoagulant used in the collection of blood specimens and is attractive because it does not distort cell morphology. It acts as an anticoagulant by chelating calcium ions (Factor IV in the coagulation cascade). Pseudothrombocytopenia is caused by an antiplatelet autoantibody to an epitope of glycoprotein IIb. This epitope is normally hidden but becomes available for binding by the aforementioned autoantibody when calcium concentrations drop, as occurs in EDTA-containing blood tubes. Binding by this autoantibody induces platelet aggregation, as seen in the image shown in this week’s challenge. Moreover, the autoantibody is often a cold-agglutinin that causes more platelet aggregation at room temperature.
In the absence of iatrogenesis or unnecessary further workup, pseudothrombocytopenia is a harmless entity. It occurs in 0.1-2% of hospitalized patients and is suggested by spuriously low platelet counts, lack of clinical signs of thrombocytopenia, lack of family history of thrombocytopenia, and/or lack of alternative cause for thrombocytopenia (e.g. hematologic malignancy, hemolysis, hypersplenism). The main adverse consequence of pseudothrombocytopenia is unnecessary workup, including imaging, bone marrow biopsy, and further expensive laboratory workup. Thus, consideration of pseudothrombocytopenia should be made when a spurious low platelet count is encountered.
As seen in this week’s image, analysis of the peripheral blood smear reveals platelet aggregation. Diagnosis of pseudothrombocytopenia can be confirmed by recollection of the blood sample in a blood collection tube without EDTA, typically a tri-sodium citrate dihydrate buffered tube (i.e. blue-top tube). If the blood count returns as normal, pseudothrombocytopenia is likely the diagnosis. Citrate-buffered tubes are typically used for coagulation testing. Citrate acts as an anticoagulant via calcium chelation. Unlike EDTA, the reversal of this anticoagulation is easily obtained in the lab by adding more calcium and other specific reagents. Moreover, pseudothrombocytopenia rarely occurs with citrate.
On Monday, we will post an image challenge of the week. We will post the answer on Friday. As the year progresses, the cases will get progressively harder.
Case: A 35 year old white woman is admitted for an elective cholecystectomy for symptomatic cholelithiasis and is found to have a platelet count of 90,000 platelets per microliter of blood. She denies any bleeding history or fatigue. Her exam is without findings of petechiae, bruising, or organomegaly. Her other laboratory findings are unremarkable.
Her peripheral smear demonstrates the following:
What diagnosis is suggested by this finding? What can you do to confirm this diagnosis? How would you change your management based on the diagnosis?
Tune in Friday for the answers!