TTP or Not TTP?

1Pritzker School of Medicine, University of Chicago, Chicago, IL
2University of Chicago, Chicago, IL
3University of Chicago, Chicago, IL
4University of Chicago, Chicago, IL

Meeting: Hospital Medicine 2008, April 3-5, San Diego, Calif.

Abstract number: 154

Case Presentation:

A 25‐year‐old woman with a history of systemic lupus erythematosus (SLE), hypertension (HTN), and class IIIA lupus nephritis was admitted to the ICU for a generalized tonic‐clonic seizure. Her blood pressure was 250/150, and a head CT showed an acute intracerebral hemorrhage in the right basal ganglia and thalamus. The patient was also suffering from acute renal failure (creatinine 6.8 mg/dL [baseline 0.8 mg/dL]); anemia (Hgb 7.6 g/dL [baseline 11.2 g/dL]); and thrombocytopenia (platelet count 39,000/μL [baseline 325,000/μl]). The patient's LDH was 474 U/L, haptoglobin was <20 mg/dL, and a blood smear showed several schistocytes. A direct Coombs antibody test was negative. The ADAMTS13 assay confirmed low ADAMTS13 function (<5%) and high ADAMTS13 inhibitor level at 2.4 units. Plasma exchange was initiated for thrombotic thrombocytopenic purpura (TTP). A nitroprusside drip was used to stabilize her HTN, and the patient was eventually transferred to a rehabilitation facility.

Discussion:

The triad of acute renal failure, microangiopathic hemolytic anemia, and thrombocytopenia suggested thrombotic micro‐angiopathy. This could be a result of either TTP or malignant hypertension in our patient with worsening lupus nephritis. To diagnose TTP, the ADAMTS13 functional and inhibitor assays were used. These tests are based on a recent groundbreaking discovery. In 1998, researchers found that idiopathic TTP is characterized by autoantibodies to ADAMTS13, a zinc‐containing metalloprotease enzyme that cleaves von Willebrand Factor, rendering it inactive. ADAMTS13 inhibitor assay tests for autoantibodies by mixing heat‐treated patient plasma with normal plasma and measuring residual ADAMTS13. Normal individuals have functional ADAMTS13 > 67% and ADAMTS13 inhibitor < 0.4 units. Because ADAMTS13 levels vary widely (22%‐172%) in SLE patients, the functional assay should not be used alone to diagnose TTP. For this reason, ADAMTS13 inhibitor assay is used in conjunction with the functional assay to diagnose TTP in SLE patients.

Conclusions:

Although the annual incidence of TTP in the general population is only 4‐11 cases per million, a much greater proportion of SLE patients (roughly 1%‐4%) will experience a TTP episode in their lifetime. This prevalence, coupled with the near 90% mortality rate of TTP without plasma exchange, makes early recognition and treatment of TTP in SLE patients essential. To diagnose TTP in SLE patients, both ADAMTS13 functional and inhibitor assays should be performed.

Author Disclosure:

N. Kapoor, none; T. Nam, none; D. VanderWeele, none; V. Arora, none.

To cite this abstract:

Kapoor N, Nam T, VanderWeele D, Arora V. TTP or Not TTP?. Abstract published at Hospital Medicine 2008, April 3-5, San Diego, Calif. Abstract 154. Journal of Hospital Medicine. 2008; 3 (suppl 1). https://www.shmabstracts.com/abstract/ttp-or-not-ttp/. Accessed May 26, 2019.

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