When LDL Cholesterol Is Not LDL Cholesterol: LpX, A Clinical Lesson

Biochemical exploration of cholestasis: interpretation, traps and interferences

We described the case of a 33-year-old patient who presented to the emergency department with non-febrile jaundice associated with epigastric pain. He suffered from acute non-severe alcoholic hepatitis and cholestasis. Biochemical investigations highlighted a huge elevation of the alpha-1-globulins fraction with an unexpected peak in the alpha-1-globulins area in serum protein electrophoresis, a severe hypercholesterolemia without xanthelasmas nor cholesterolomas. Investigations revealed an abnormal lipoprotein, Lipoprotein X (LpX) that can be responsible for the hypercholesterolemia, but also interferes with biochemical tests like direct low-density lipoprotein cholesterol, albumin, and serum electrolytes assays. LpX is an abnormal lipoprotein, which can be present in patients with liver dysfunction, notably in cholestasis-related conditions where the metabolism of plasma lipoproteins is altered. Cholestasis prevents the normal formation of bile acids, leading to the formation of LpX, which is rich in phospholipids and unesterified cholesterol, but poor in esterified cholesterol, triglycerides and proteins. The accumulation of LpX can lead to severe hypercholesterolemia, but this remains uncommon and data regarding the pathophysiology and incidence of this disease is scarce. The laboratory investigation of patients with suspected Lpx can be challenging, due to the lack of available methods for measurement of LpX. In conclusion, LpX-induced hyperlipidemia must be identified to prevent interference in results for a number of biochemical tests, and additionally to improve patient care.

Case report: Unusual and extremely severe lipoprotein X-mediated hypercholesterolemia in extrahepatic pediatric cholestasis

BACKGROUND

Lipoprotein X (LpX) - mediated extremely severe hyperlipidemia is a possible feature detectable in children with syndromic paucity of intralobular bile ducts (Alagille syndrome) but rarely in other types of intra- and/or extrahepatic infantile cholestasis.

CASE PRESENTATION

Here we report on a previously well 18-month child admitted for cholestatic jaundice and moderate hepatomegaly. Laboratory tests at entry showed conjugated hyperbilirubinemia, elevated values of serum aminotransferases, gamma-glutamyl transpeptidase (GGT) and bile acids (100 folds upper normal values). Extremely severe and ever-increasing hypercholesterolemia (total cholesterol up to 1,730 mg/dl) prompted an extensive search for causes of high GGT and/or hyperlipidemic cholestasis, including an extensive genetic liver panel (negative) and a liver biopsy showing a picture of obstructive cholangitis, biliary fibrosis, and bile duct proliferation with normal MDR3 protein expression. Results of a lipid study showed elevated values of unesterified cholesterol, phospholipids, and borderline/low apolipoprotein B, and low high-density lipoprotein-cholesterol. Chromatographic analysis of plasma lipoproteins fractions isolated by analytical ultracentrifugation revealed the presence of the anomalous lipoprotein (LpX). Magnetic resonance cholangiopancreatography and percutaneous transhepatic cholangiography showed stenosis of the confluence of the bile ducts with dilation of the intrahepatic biliary tract and failure to visualize the extrahepatic biliary tract. Surgery revealed focal fibroinflammatory stenosis of the left and right bile ducts confluence, treated with resection and bilioenteric anastomosis, followed by the rapid disappearance of LpX, paralleling the normalization of serum lipids, bilirubin, and bile acids, with a progressive reduction of hepatobiliary enzymes.

CONCLUSION

We have described a unique case of focal non-neoplastic extrahepatic biliary stenosis of uncertain etiology, presenting with unusual extremely high levels of LpX-mediated hypercholesterolemia, a condition which is frequently mistaken for LDL on routine clinical tests.