Unusual Case of Hepatic Sinusoidal Obstruction Syndrome Induced By Low Dose Oral Cyclophosphamide
Authors: Gaudel Pramod , Snyder Jordan , Yacoub Abdulraheem 
Published: November 2020

Hepatic sinusoidal obstruction syndrome (SOS) has been reported in patients receiving high dose intravenous (IV) cyclophosphamide especially as a part of preparative regimen for hematopoietic stem cell transplantation. Hepatic SOS from low dose oral cyclophosphamide has not been reported. Here we present a rare case of hepatic SOS induced by low dose oral cyclophosphamide.
A 78-year-old male with history of coronary artery disease status post coronary artery bypass graft (CABG) was initially seen in hematology clinic for evaluation of normocytic anemia. During workup, bone marrow biopsy revealed NK cell large granular lymphocytic leukemia (LGL). He was then started on low dose oral cyclophosphamide 50 mg daily. After 2 months, his dose was reduced to 25 mg daily due to severe neutropenia. He then tolerated cyclophosphamide well and his hemoglobin (Hb) improved from his baseline 8 gm/dl to 12 gm/dl in 4 months. After 6 months of treatment, he was admitted to the hospital for abdominal distension, ascites and 15 pounds weight gain over 3 weeks. Labs most prominent on admission were Hb of 12.5 gm/dL , WBC 5.3 x 103/µL, Platelets 197 x 103/µL, total bilirubin 1.6 mg/dL, aspartate aminotransferase (AST) 89 U/L , alanine aminotransferase (ALT) 35 U/L and alkaline phosphatase (ALP) 283 U/L. Workup of ascites included abdominal paracentesis which revealed serum ascites albumin gradient(SAAG) &lt;1.1 and fluid cytology was negative for carcinoma. Ultrasound of abdomen showed diffuse parenchymal heterogeneity and increased echogenicity of liver with patent hepatic vessels with normal direction of blood flow. Echocardiogram revealed preserved left ventricular systolic function with estimated left ventricular ejection fraction of 60%. He then underwent transjugular liver biopsy which revealed chronic lymphoproliferative disorder of NK cells, prominent centrilobular sinusoidal dilatation and congestion, lobular disarray, cholestasis and sinusoidal fibrosis suggestive of veno-occlusive disease secondary to drug/toxin induced liver injury. The Naranjo adverse drug reaction probability scale indicated a probable relationship between hepatic SOS and cyclophosphamide. Cyclophosphamide was held. Bone marrow biopsy showed the patient was in remission. His liver enzymes are improving and hematologic counts continue to be stable while on observation.
High dose of IV cyclophosphamide given as myeloablative therapy in combination of total body irradiation or busulfan (or other agents) in preparation for hematopoietic stem cell transplantation can induce hepatic SOS, which can be severe leading to acute liver failure and death. The diagnosis is usually based on clinical features of tender hepatomegaly, weight gain, ascites and jaundice. Liver biopsy is usually diagnostic. Mechanism of injury is related to direct toxic effects of cyclophosphamide on sinusoidal cells in the liver, causing their necrosis and release into the sinusoids, obstruction and obliteration of hepatic veins. This case demonstrates that hepatic SOS can also be caused by low dose oral cyclophosphamide. Given this rare occurrence, it is prudent for the clinicians to keep an open mind and consider hepatic SOS as a potential side effect even with oral cyclophosphamide.

Disclosures
Yacoub: Novartis: Speakers Bureau; Agios: Honoraria, Speakers Bureau; Incyte: Speakers Bureau; Hylapharm: Current equity holder in private company; Cara Therapeutics: Current equity holder in publicly-traded company; Ardelyx: Current equity holder in publicly-traded company; Dynavax: Current equity holder in publicly-traded company; Roche: Other: Support of parent study and funding of editorial support.