Niemann-Pick Disease and the Sea blue
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: A rare
lysosomal storage disorder causing histiocytic hyperplasia due to enzymatic defect.
There is accumulation of lipid in cells of mononuclear phagocytic
system and central nervous system.
Microscopic images of liver in Niemann-Pick disease 1 and 2.
Image (1) shows clusters of foam cells. Image (2) highlights the pale staining clusters of sphingomyelin containing foam cells in a backround of PAS positive glycogen containing hepatocytes.
Niemann-Pick disease is characterized by hepatosplenomegaly and mental retardation.
The disease classically affects infants.
Sphingomyelinase-deficient type A variant is the most common form.
Types A and C are always associated with severe neurological involvement.
Niemann-Pick disease types A and B are related disorders that are associated with a deficiency of sphingomyelinase and consequent accumulation of sphingomyelin in mononuclear phagocytes and many other cell types.
Type B Niemann-Pick disease (NPD-B) is a rare, autosomal recessive, lysosomal storage disorder with a broad range of disease severity.
Type B variant is characterized by hepatosplenomegaly with progressive hypersplenism, worsening atherogenic lipid profile, gradual deterioration in pulmonary function, and liver dysfunction.
Niemann-Pick type C disease is a sphingolipid-storage disorder that results from inherited deficiencies of intracellular lipid-trafficking proteins, and is characterised by an accumulation of cholesterol and glycosphingolipids in late endosomes and lysosomes.
Niemann-Pick type D disease ("Nova Scotian" form ) is a progressive neurodegenerative disorder characterized by the accumulation of tissue cholesterol and sphingomyelin.
This disorder is relatively common in southwestern Nova Scotia.
Pathology of Niemann-Pick Disease :
- The histiocytes accumulate sphingomyelin, which is derived from cell membranes and myelin sheaths.
The histiocytes of Niemann-Pick disease appear foamy in microscopic section in constrast to the more distinctive apparance of 'Gaucher cell' which appears striated ( crumpled tissue paper type appearance).
- In Niemann-Pick disease, the globules in the cytoplasm are small and uniform in size. It is also described as mulberry-like in appearance.
The sphingomyelin-containing histiocyte stains blue when stained with Giemsa stain and this blue granular, foamy appearing histiocyte has been called 'sea-blue histiocyte'.
In frozen sections of fresh tissue the vacuoles stain for fat with Sudan black B and oil red O. Niemann-Pick cells are CD-68 positive histiocytes.
Diagrams of sea-blue histiocytes (1 and 2)
- Brain and eye: In brain the gyri are shrunken and sulci are widened. Diffuse neuronal involvement lead to cell death and shrinkage of the brain.
All parts of nervous system is affected.
Diagram of the brain
There is vacuolation and ballooning of the neurons.
In the eye there is a retinal cherry-red spot similar to that in Tay-Sachs disease.
It is due to accumulation of sphingomyelin.
- Spleen, Liver, Lymphnodes and Bone marrow: Massive accumulation of lipid-laden cells of the mononuclear phagocytic system, giving rise to huge splenomegaly (sometimes 10 times its normal weight), enlargement of liver and lymph nodes.
There is infiltration of the bone marrow.
The colour of these organs is paler due to accumulation of sphingomyelin.
Diagram of liver , lymphnodes, spleen and bone marrow
- Visceral involvement affecting the gastrointestinal tract, lungs, and tonsils have been reported.
Sea Blue Histiocytes:
The appearance of the sea blue histiocyte is nonspecific and similar histiocytes can be found in the spleen or marrow in many different hereditary and acquired conditions.
Sea blue histiocytes may be present in small numbers in normal bone marrow.
These are increased in any disorder associated with massively increased intramedullary cell destruction (Example- Chronic myelogenous leukemia.)
Sea Blue Histiocyte Syndrome:
The syndrome of splenomegaly of unknown cause with pupura secondary to hypersplenism manifested by severe thrombocytopenia has been referred to as Sea Blue Histiocyte Syndrome.
The macrophages in Sea Blue Histiocyte Syndrome stains blue in Romanowsky stained smears and yellow to tan in sections stained with Hematoxylin and eosin stain.
Positive reaction is noted with PAS and Sudan black B stains. The substance appears to be ceroid hence "Sea Blue Histiocyte Syndrome" is also known as "Ceroid Histiocytosis".
Ceroid, a form of lipofuchsin results from the peroxidation and polymerization of unsaturated lipids.
It is present in macrophages as a light, yellow or brown autofluorescent pigment and is usually associated with lipid vacuoles.
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