History: A 31 year-old trauma patient underwent a splenectomy to remove a lacerated spleen. The organ was enlarged, weighing 500 grams and had overall diameters of 19.5 x 10.5 x 3.5 cm. The parenchyma was uniformly firm and red with indistinct follicular and trabecular markings. No focal lesions were identified.
Microscopically, the red pulp was expanded, largely by a macrophage infiltration (Fig. 1). These cells had bubbly, vacuolated cytoplasm giving the cytoplasm a “clear cell” appearance (Figs. 2,3). Special stains included:
PAS (+/- diastase) Faintly positive
Giemsa Rare ceroid-containing (‘sea blue’) histiocytes
Diagnosis: Lipid Storage Disease, Consistent With Niemann-Pick Disease
Melissa Skaugset, MSIV and Donald R Chase MD
Department of Pathology, Loma Linda University and Medical Center, and
California Tumor Tissue Registry, Loma Linda, California
Discussion: Niemann-Pick disease is a disorder of lipid metabolism and storage that causes accumulation of sphingomyelin in tissue macrophages (histiocytes) due to a deficiency of acid sphingomyelinase. Patients can be classified both by clinical features and by genetic mutation. Four types have been identified. Types A and B are associated with a defect in the SMPD1 (acid sphingomyelinase) gene with type A being the neuronopathic form and B the non-neuronopathic form. Mutations in both the NPC1 and NPC2 genes cause so-called type C disease. All forms have autosomal recessive inheritance.
Clinically, presentation varies with type of disease, with Type A showing the most severe impairment characterized by hepatomegaly, jaundice, failure to thrive, seizures, and mental retardation in infancy. Children with Type A disease rarely survive past 18 months. Type B disease has no neural involvement, so patients typically present later, most commonly in late childhood/early teens. These children present with poor growth, hepatosplenomegaly, recurrent lung infections, and may have lab abnormalities, including elevated lipids and cholesterol and thrombocytopenia.
Type C disease differs significantly from A or B disease in both pathologic mechanism and clinical presentation. The defect in the NPC gene causes failure of a transporter in the endosomal-lysosomal system of cells, causing a buildup of cholesterol and glycolipids in lysosomes. The clinical presentation of Type C disease varies widely. In children who manifest disease, progressive neurological deficits develop which may or may not be associated with hepatosplenomegaly or jaundice. Neurologic disease is diffuse and has been documented to include dysphagia, dysarthria, ataxia, seizures, gaze palsies, ptosis, dystonia, hypotonia, psychiatric disorders, and dementia. Types A, B, and C are increased in Ashkenazi Jews.
A fourth form exists, occurring mostly in a population from Yarmouth County, Nova Scotia. This Type D or “Nova Scotian” form has been demonstrated to also have a defect in the NPC1 gene. Interestingly, it seems that those with Type D disease share common ancestry with Joseph Muise (born in Nova Scotia in 1679) and his wife Marie Amirault (born in Nova Scotia in 1684), making one or both of them the likely carrier of original mutation causing disease in this population. It is unclear why what may be a new mutation in either Joseph or Marie resulted in such a high carrier rate, but close communities (this is seen in the Acadian population of Nova Scotia) with the resultant limitation in genetic diversity may have played a role. Once a high carrier rate was achieved, it became possible for this autosomal recessive disease to manifest as children of dual carrier parents who were homozygotic for the disease causing gene, therefore having clinical disease. Similar patterns of emergence of rarer genetic diseases have been seen in populations such as the Old Order Amish (Ellis-Van-Crevald syndrome), French Canadian Chicoutimi (hereditary tyrosinemia). More recently there has been an emergence of fumarase deficiency noted in the Fundamentalist Church of Jesus Christ of Latter Day Saints particularly at the Arizona-Utah border, that shows similar patterns. This is also and autosomal recessive disorder and in a community is able to definitively trace its ancestry to a limited group of church/community leaders, however it has not yet been elucidated when the defective gene was found in the founding members or introduced to the community at a later date.
Pathologic specimens from patients with Niemann-Pick disease may be limited to bone marrow biopsies if the diagnosis is suspected clinically. These are used to confirm disease and to help guide additional biochemical and genetic testing. When surgical specimens are available, gross findings include enlarged spleens and livers, with diffuse involvement of the liver and spleen evident on cut sections. Expansion of the cordal macrophages gives a firm texture to the cut surface of the spleen. The tissue is frequently pale and homogeneous on cross section. The normal markings of the spleen are made less distinct by the proliferation of histiocytes. Later findings in hepatic involvement include nodular fibrosis of the liver.
Histologically, Niemann-Pick cells are enlarged with accumulation of small vacuoles containing sphingomyelin (Figs 2,3). These give the cells a foamy or bubbly appearance and make them lighter in color than the similar appearing Gaucher cells. Niemann-Pick cells are CD-68 positive histiocytes. PAS staining is only faintly positive, but Sudan Black B and Oil Red O are positive, indicating that neutral fat contained in the vacuoles. These lipid deposits are birefringent and have yellow-green fluorescence in UV light. Electron microscopy shows lamellated structures in the lysosomes (similar to myelin figures) and may also demonstrate “zebra bodies”, parallel lamellated structures in the cytoplasm. Giemsa staining can highlight “sea blue” histiocytes containing ceroid, most common in Type C disease.
Many of the congenital enzyme deficiencies cause accumulation of material within the histiocytes of the spleen, liver, and CNS, causing enlargement of the parenchyma and the clinical manifestations of the disease. Many cases are diagnosed using tests for enzyme activity, but histologic diagnosis is often the mainstay of initial evaluation. Histology allows for guidance of enzymatic and/or genetic testing by helping differentiate the cells noted in different metabolic diseases. The cells of Gaucher disease are identified by their “crinkled tissue paper” cytoplasm, seen best on touch imprints. Niemann-Pick histiocytes have bubbly, multi-vacuolated cytoplasm, as do the gangliosidoses and mucopolysaccharidoses (i.e. Tay-Sachs, Hunter’s, or Hurler’s disease), however the latter with ballooned cells makes it distinct from the former. Fabrys, Wolmans, and von Gierkes disease all have foamy appearing histiocytes. Hermansky-Pudlak syndrome causes ceroid accumulation, leading to sea blue colors in the cells, though it should be noted that ceroid containing histiocytes are also seen on other, more common diseases (and in fact were noted in this case) and should therefore be considered somewhat non-specific. Evaluation by of enzyme activity is required for more precise classification of disease.
Because treatment regimens are very limited, patient prognosis depends more on the type of disease, rather than on the treatment. Type A disease almost invariably ends in infantile death. Type B patients may live significantly longer, but have significant morbidity, particularly due to lung involvement. Bone marrow transplantation has been used in Type B patients with some success. It is thought that Types C and D may benefit from a low cholesterol diet, though this has not been demonstrated in clinical studies. The prognosis for Types C and D is widely variable, with some childhood deaths. The less severely affected patients may live into adulthood. An ongoing clinical trial of enzyme replacement therapy uses a recombinant human acid aphingomyelinase, and to date, this protocol shows the greatest promise for improving outcomes in the most severe forms of the disease.
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