Challenge your diagnostic skills

Question 1 of 3 – What is your next step?

• Presentation: A 59-year-old woman was hospitalized in April 2019 when she presented with abdominal pain, purpura, and gross hematuria. The patient reported that the symptoms had been triggered by the sudden drop in temperature caused by a cold weather front.
• History: The patient had experienced cryoglobulinemia, thrombotic microangiopathy (TMA), and acute kidney injury 2 years earlier.
• Physical examination: revealed lower extremity purpura and abdominal tenderness. Organomegaly was not detected. No neurologic deficits were noted.
• Laboratory tests: revealed microangiopathic hemolytic anemia, thrombocytopenia, elevated lactate dehydrogenase (LDH) levels, slightly elevated peripheral blood lymphocyte count, schistocytes on a peripheral blood smear, elevated serum creatinine, and extremely low serum concentrations of complement 3 (C3) and complement 4 (C4). The direct Coombs test and antiplatelet antibody test were negative. Urinalysis showed proteinuria and hematuria.

The patient was initially diagnosed with complement-mediated TMA and underwent plasmapheresis. Despite clinical disease remission, the cryoglobulinemia and low serum C4 levels persisted.

(A) Skin purpura and soy-colored urine. (B) The remission of purpura and hematuria. (C) Timeline of serum creatinine (Scr) and lactate dehydrogenase (LDH) and their relationships with plasmapheresis (arrows indicated plasmapheresis).

Laboratory results:

Hemoglobin: 9.5 g/dL (11.5–15.0 g/dL); platelet count: 94 × 10⁹/L (125–350 × 10⁹/L); LDH: 284 U/L (100–240 U/L). direct Coombs test: negative; antiplatelet antibody test: negative; peripheral blood lymphocyte count: 3.34 × 10⁹/L (1.1–3.2 × 10⁹/L); blood smear: 0.3% schistocytes; serum creatinine: peak of 187 μmol/L (44–133 μmol/L); C3: 0.372 g/L (range 0.6–1.5 g/L); C4: below the detection limit; urinalysis: proteinuria (2+) and hematuria (15–20 red blood cells per high-power field).

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