Using Ultrasound Elastography to Predict Development of Sinusoidal Obstruction Syndrome

Hepatic sinusoidal obstructive syndrome (SOS) is a complication of blood and marrow transplant (BMT) that is associated with high morbidity and mortality. 57,000 patients in the United States and Europe undergo BMT annually, and SOS affects up to 15% of these patients. SOS pathogenesis is thought to be caused by damage to the hepatic venous endothelium due to the preparative regimen used before BMT. This damage results in obstruction of blood flow through the liver. Pathology shows collagen deposition in the sinusoids and fibrosis of venous lumens. The severity of the disease is correlated to the number and severity of the histological changes. Mild and moderate SOS can resolve with supportive treatment. Severe SOS (30% of SOS) is commonly associated with multi-organ failure and has a mortality rate of 80% despite available prophylaxis and treatment (Table 1).

SOS is most commonly defined by two clinical criteria: the modified Seattle criteria and the Baltimore criteria (Table 2). The modified Seattle criteria state that at least two of the following criteria must be present within 20 days of BMT: bilirubin > 2mg/dL; hepatomegaly and/or ascites; and/or weight gain > 5% above baseline weight. Pediatric SOS incidence in BMT is 20% and is higher compared to adults. Death or multi-organ dysfunction affects 30-60% children who develop SOS. The most common definition of severe SOS is retrospective, namely death from SOS-related causes or persistent multi-organ dysfunction at 100 days post BMT. However, the European Society for Blood and Marrow Transplantation has proposed a new prospective SOS grading scheme that will likely become standard of care since it is pediatric patient specific and it is can be performed prospectively and thus can guide treatment.

Recently, a promising drug for SOS treatment has been discovered, defibrotide, which is a DNA derivative from porcine intestine that protects and repairs endothelial cells. Prior trials showed that defibrotide decreased the incidence of multi-organ failure and death from SOS. The main caveat is that treatment must be initiated very close to the time of clinical diagnosis using the Baltimore criteria to be effective. A study showed that 31/33 (94%) patients had complete remission of their SOS when treated with defibrotide <3 days after diagnosis, whereas only 3/12 (25%) patients had complete remission when treated >3 days of diagnosis. However, universal prophylaxis is infeasible due to high drug costs ($155,000 for patient) (2016). There is a critical need for an early and effective SOS diagnostic test that can identify patients who would benefit from defibrotide treatment.

Several adult and pediatric prospective studies have evaluated the efficacy of grayscale and Doppler ultrasound (US) in diagnosing SOS and have concluded that the clinical criteria are superior to US criteria for SOS diagnosis. The main reason for this conclusion is that conventional US is able to diagnose SOS only after the clinical diagnosis. This research has resulted in multiple recent guidelines recommending US only for confirming clinical diagnoses or following disease progression and not for primary diagnosis. Ultrasound shear wave elastography (SWE) has been shown to effectively diagnose passive hepatic congestion. Fontan physiology is the best studied example. SWE values markedly increased after the Fontan operation. This surgery connects the hepatic venous circulation to the pulmonary arteries exposing the liver to increased resistance from the pulmonary circulation thereby increasing hepatic venous congestion. Additionally, the effect sizes in the Fontan studies are large compared with the effect sizes in hepatic fibrosis studies. The common thread of hepatic venous congestion between Fontan physiology and SOS physiology led us to hypothesize that SWE could be useful in SOS diagnosis. Additionally, preliminary SWE studies in adults showed that it might be useful in the setting of SOS.

Data Collection Procedures Candidates for the study will be identified by a BMT physician taking care of the patient and will be identified as a potential candidate for the study. Subjects will be approached for consent by a member of the research team prior to start of conditioning regimen. Consented subjects will have demographic, laboratory and clinical data collected from the chart at each ultrasound time point.