Thrombotic but Thrombocytopenic

Considering this case as a whole, what is the most likely diagnosis regarding the cause of the rash?

You are extremely worried about this patient and request that ITU review her as part of your initial management. You also make a referral to the obstetric registrar.

The ITU registrar reviews the patient and is just as concerned as you. After a quick chat with her consultant, she prepares a bed and whisks the patient over to ITU. She is happy for the obstetric registrar to review the patient there.

Which one of the following treatment strategies is not appropriate for this patient?

A few days later, you are reviewing the patient’s progress at a workstation with some interested colleagues and are pleased to find that the patient is improving and is about to be stepped down soon.

You note that the patient has had both an ADAMTS13 activity assay and anti ADAMTS13 antibody levels done while in ITU. ADAMTS13 activity is <10% and the antibody levels are high – which indicates that the TTP is autoimmune and acquired as opposed to hereditary (Upshaw-Schulman syndrome). You proceed to impress your colleagues by informing them that the pathogenesis of TTP involves a deficiency in a protease synthesised in the liver known as ADAMTS13 (A Disintegrin And Metalloproteinase with a ThromboSpondin type 1 motif, member 13).^1,2

You teach them that ADAMTS13 is involved in cleaving von Willebrand factor (vWF) – a plasma glycoprotein that binds platelets at sites of vascular injury. Reduced ADAMTS13 activity therefore means that there is increased vWF activity specifically due to the persistence of ultra-large von Willebrand factor multimers (ULVWF). This in turn leads to increased platelet aggregation (causing thrombosis) and therefore reduced platelets in the circulation (thrombocytopenia).^1,2

The ADAMTS13 deficiency also definitively differentiates TTP from HUS since the typical form of HUS is caused by Shiga toxin and the atypical form is complement-mediated.

As part of your informal lesson, you ask them to guess the mortality rate of TTP if left undiagnosed and untreated. What is it?