Case 1 -

Heavy Siderosis Andrew Clouston

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Clinical History The patient was a 40 year old dentist with a history of alcoholic liver disease and decompensated cirrhosis. He was transplanted and the section is from the explant. Apart from some acquired red cell spurring requiring 2 transfusions in the preceding 12 months, there was no history of recurrent transfusions or iron supplementation. Testing for HFE mutations was performed at a later time. Case 1 - Figure 1 Low power view showing established cirrhosis. Case 1 - Figure 2 Medium power view showing pigment in hepatocytes Case 1 - Figure 3 Medium power view showing an area of nodular dropout, indicating that active parechymal refashioning is ongoing in this liver. The lost nodule is replaced by a ductular reaction. Small clusters of hepatocytes remain focally. Case 1 - Figure 4 Pigment accumulation is mainly hepatocellular Case 1 - Figure 5 Perls stain showing grade 4 siderosis Case 1 - Figure 6 Perls stain showing iron accumulation in bile ducts and ductules. Case 1 - Figure 7 PAS stain after diastase digestion showing globules of alpha-1-antitrypsin. The patient was PiMZ. The globules were irregularly distributed. Commentary The case demonstrates heavy siderosis, predominantly hepatocellular and in biliary ductules, in the context of end-stage cirrhosis. The pattern is certainly similar to that seen in hereditary hemochromatosis (HH), but when genotyping became routinely available several years later and was performed, the patient did not have either of the typical mutations in the HFE gene (C282Y or H63D). This commentary will discuss hepatocellular iron overload when HH due to HFE mutation has been excluded. i. Other forms of hereditary hemochromatosis Recent advances in the understanding of iron transport have clarified the genetic basis of the rarer forms of HH. Central to the control of iron homeostasis is the iron downregulator hepcidin, produced by hepatocytes. Its expression is modified by HFE protein and transferrin receptor 2 (TfR2) but the mechanisms underlying this are still under investigation. Another protein, hemojuvelin (HJV), is a crucial co-receptor for hepcidin transcription. Therefore, mutation of any of these can cause HH [1]. Hepcidin expression is increased when iron is replete in the hepatocytes and circulating iron pool. Thus, Pietrangelo has pointed out that hepcidin is a little like insulin, increasing in response to increased iron (analogous to insulin in the case of glucose). Conversely, when hepcidin is deficient, iron absorption is allowed to occur unchecked. Circulating hepcidin binds to ferroportin in mucosal and reticuloendothelial cells, leading to its degradation. As ferroportin is the chief iron exporter protein from cells, this leads to retention of iron in the mucosal or reticuloendothelial cell. Iron loading disorders result when there are inappropriately low levels of hepcidin (eg mutations in HFE, TfR2, HAMP (the hepcidin gene) or HJV), or if ferroportin mutation prevents iron export from cells, mainly macrophages (Table 1). Thus, although HFE mutation is the major cause of iron overload, mutation of the above proteins gives a similar histological picture, dominated by hepatocellular deposition as well as iron loading throughout the body. An exception is ferroportin mutation, causing hemochromatosis type 4. With an autosomal dominant inheritance, ferroportin mutation can produce two phenotypic patterns of iron deposition depending on the specific mutation, which governs the activity and location of ferroportin in the cell. As this protein controls iron transport out of enteric mucosal cells and also other cells such as macrophages, one pattern resembles classical HH and the other, more common, shows a mixed deposition in hepatocytes, reticuloendothelial cells (Kupffer cells, bone marrow and splenic macrophages, and enterocytes. The latter pattern is associated with low transferrin saturation and resistance to phlebotomy therapy. Although mutation of one or the proteins listed in Table 1 is a possible cause of the changes seen in this case, with the exception of HFE mutation these disorders are very rare. However, data from the last decade suggest that heavy hepatic iron overload mimicking HH, that is grade 3-4 siderosis or hepatic iron index >1.9, occurs in about 8-12% of patients with end-stage cirrhosis coming to liver transplantation [2, 3, 4, 5]. Clearly, other mechanisms must be responsible. ii. Iron overload in cirrhosis Although overlooked, hepatic iron accumulation is common in late cirrhosis; this was initially pointed out by Ludwig in 1997 [2]. Studies published to date have had similar results, describing some degree of iron deposition in many livers removed at the time of transplantation (around 30-40% of explants), but also heavy siderosis mimicking HH in about 10% of explants. The mimicry can be striking, including heavy hepatocellular deposition, relative sparing of kupffer cells, and deposition in structures such as ductules, endothelial cells and vessel walls. An analysis of prior biopsies suggests that the iron accumulation may occur relatively rapidly over a period of only 12-18 months. The current case showed only patchy grade 1 iron in a biopsy taken 15 months earlier. iii. Spur cell anemia as a potential cause or cofactor of marked siderosis It is pertinent to ask why this marked siderosis occurs. Non-HH siderosis is described in a number of scenarios (hereditary haematological disorders, dietary, parenteral/transfusional, acquired anemias, porphyria cutanea tarda, African siderosis). Parenteral iron overload typically produces siderosis that is prominent in reticuloendothelial cells, and in most of the causes above the clinical history will be informative. In the case of end-stage cirrhosis, the predominantly hepatocellular loading is likely to reflect a relationship between decreasing liver mass, abnormal hepcidin homeostasis and stepwise deterioration of hepatic function related to sepsis and intrahepatic vascular events. As hepcidin is produced by the hepatocytes, reduced liver mass in cirrhosis may translate into reduced hepcidin expression. Additionally, the progression of cirrhosis from early to late phases is a reflection of intrahepatic vascular events leading to zonal ischemia and dropout of nodules (parenchymal "extinction") [6]. Hypoxia is another cause of reduced hepcidin expression. Finally, several studies found an association between spur cell anemia, severe end-stage liver disease and heavy siderosis in liver explants [4, 5]. Red cell spurring is seen in advanced cirrhosis and occurs because of abnormal cholesterol metabolism by the diseased liver, resulting in red cell membrane spurring and hemolysis. It occurs in bouts that correlate with episodes of functional deterioration; in some cases it requires transfusion. The combined hypoxia as well as erythropoietic drive is probably an additional cause of reduced hepcidin expression. Thus, in late cirrhosis, as nodules progressively drop out and liver function deteriorates, it seems likely that multifactorial suppression of hepcidin allows free mucosal absorption of iron and deposition in tissues. This can lead to grade 4 iron deposition in under 12 months, and gives a predominantly hepatocellular accumulation (rather than Kupffer cells as would be expected) that is strikingly similar to HH. A diagnostic clue is the deposition of iron in hepatocytes, ductules, vessels and endothelium but not in larger anatomical bile ducts. iv. Alpha-1 antitrypsin (a1AT) globules PAS-positive, diastase-resistant globules are present in conspicuous numbers in some parts of the liver explant. The patient was heterozygous (PiMZ) and this demonstrates how a1AT globules can be relatively prominent in some heterozygous patients. There were no globules in an earlier biopsy. The jury is still out on the role of heterozygosity for a1AT deficiency in exacerbating another chronic liver disease. It is tempting to speculate that there may have been a role for ATZ in accelerating the deterioration of liver function, precipitating the red cell spurring and indirectly contributing to the iron loading in this patient. Practice points 1. Non-HFE hereditary hemochromatosis occurs when the genes for hepcidin, hemojuvelin, ferroportin, transferrin receptor-2 or caeruloplasmin are mutated. Others may remain to be discovered. These genes encode proteins that are intimately involved in iron transport and regulation. However, the mutations are very rare. 2. Heavy siderosis can be seen in end-stage cirrhosis due to hepatocellular (but generally not biliary) disease. It is likely that multifactorial inhibition of hepcidin expression (by liver hypoxia, reduced liver mass and increased erythropoiesis in the face of red cell spurring) leads to unregulated transport of iron across the enteric mucosal cells and heavy siderosis within 12-18 months. 3. Cirrhosis-associated siderosis occurs only late in the disease and is probably stimulated by post-cirrhotic remodeling that occurs when intrahepatic vascular events lead to nodular dropout and refashioning. Table 1. Classification of hereditary hemochromatosis and related disorders Disorder Mutation Histological pattern Type 1 HFE-associated HC Rec HFE - C282Y homozy - C282Y/H63D Hepatocellular with periportal accentuation Type 2 Juvenile HC Rec 2A - hemojuvelin 2B - hepcidin Hepatocellular with periportal accentuation Type 3 Transferrin R2 HC Rec Transferrin receptor 2 Hepatocellular with periportal accentuation Type 4 Ferroportin-assoc HC Dom Ferroportin 2 patterns occur (mutation-site dependent) a. macrophage (K cell) & hepatocyte loading b. predominantly hepatocyte loading Atransferrinemia Rec Transferrin Hepatocellular with periportal accentuation Acaerulplasminemia Rec Caeruloplasmin Hepatocellular with periportal accentuation Abbreviations: HC - hemochromatosis; Rec - autosomal recessive; Dom - autosomal dominant; K cell - Kupffer cell References Pietrangelo A. Molecular insights into the pathogenesis of hereditary haemochromatosis. 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