Hemosiderin

  Hemosiderin or haemosiderin is an abnormal microscopic pigment found in the human body. Hemosiderin is composed of iron oxide and can accumulate in different organs in various diseases. Iron is required by many of the chemical reactions in the body but is toxic when not properly contained. Thus, many methods of iron storage have developed.

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Humans typically store iron within a protein called ferritin. The form of iron in ferritin is Iron(III) oxide-hydroxide. By complexing with ferritin, the iron is made water soluble. Several diseases result in deposition of Iron(III) oxide-hydroxide in tissues in an insoluble form. These deposits of iron are called hemosiderin. Although these deposits often cause no symptoms, they can lead to organ damage.

Pathophysiology

Hemosiderin often forms after bleeding (hemorrhage) into an organ. When blood leaves a ruptured blood vessel, the cell dies and the hemoglobin of the red blood cells is released into the extracellular space. White blood cells called macrophages engulf (phagocytose) the hemoglobin to degrade it, producing hemosiderin and porphyrin.

Diseases associated with hemosiderin deposition

Hemosiderin deposition in the lungs is often seen after diffuse alveolar hemorrhage. Thus, diseases such as Goodpasture's syndrome, Wegener's granulomatosis, and idiopathic pulmonary haemosiderosis. Mitral stenosis can also lead to pulmonary hemosiderosis. Hemosiderin collects throughout the body in hemochromatosis. Hemosiderin deposition in the liver is a common feature of hemochromatosis and is the cause of liver failure in the disease. Deposition in the pancreas leads to diabetes and in the skin leads to hyperpigmentation. Hemosiderin deposition in the brain is seen after bleeds from any source, including chronic subdural hemorrhage, Cerebral arteriovenous malformations, cavernous hemangiomata. Hemosiderin collects in the skin and is slowly removed after bruising; hemosiderin may remain in some conditions such as stasis dermatitis.

Hemosiderin may deposit in diseases associated with iron overload. These diseases are typically diseases in which chronic blood loss requires frequent blood transfusions, such as sickle cell anemia and thalassemia.

Treatment

Treatment for hemosiderin focuses on limiting the effects of the underlying disease leading to continued deposition. In hemochromatosis, this entails frequent phlebotomy. In diseases such as Wegener's granulomatosis, immune suppression is required. Limiting blood transfusions and institution of iron chelation therapy when iron overload is detected are important when managing sickle-cell anemia and other chronic hemolytic anemias.