Case 1 -

Involvement by Systemic Mastocytosis Joseph Misdraji Massachusetts General Hospital Boston, MA

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Clinical history An 80 year old woman presented with a history of explosive diarrhea dating back a few months. Several months ago, she began experiencing liquid stool about once per day, but now it is up to 3 times per day, with occasional cramping pain and she is sometimes awakened by symptoms. Lately, it has become difficult for her to always reach the bathroom in time, with several incontinent episodes. She has eliminated dairy foods and most vegetables without effect. There had been a gradual weight loss over several years (from 60 kg a few years ago to 50 kg now) but now weight is stable. Pepto-Bismol has had some effect, although too much caused her constipation. No jaundice, fever, nausea, vomiting, rash or other significant skin findings. No peripheral eosinophilia; slightly elevated absolute neutrophil count but otherwise unremarkable blood counts. An exam for occult blood in stool was negative. Her medical history is significant only for hypertension, for which she takes atenolol. Evaluation for diarrhea included stool culture and O&P, both negative. She was put on Metamucil for presumed irritable bowel syndrome with slight improvement. She was referred to a gastroenterologist who performed a colonoscopy. The colon appeared normal and random biopsies were obtained. Case 1 - Figure 1 Low power view of several colonic biopsies shows patchy involvement of an infiltrative process. The biopsy on the left is largely uninvolved, whereas the one on the right shows separation of the crypts by an infiltrative process. Case 1 - Figure 2 A medium power view of a colonic biopsy shows widely spaced crypts with an infiltrate that appears confined to the lamina propria. Case 1 - Figure 3 Medium and high power views show lamina propria infiltration by eosinophils and histiocytic appearing cells. Case 1 - Figure 4 Medium and high power views show lamina propria infiltration by eosinophils and histiocytic appearing cells. Case 1 - Figure 5 Medium and high power views show lamina propria infiltration by eosinophils and histiocytic appearing cells. Case 1 - Figure 6 The infiltrate consists of a mixture of eosinophils, oval or spindle cells, and the occasional lymphocyte and plasma cell. Case 1 - Figure 7 The infiltrate consists of a mixture of eosinophils, oval or spindle cells, and the occasional lymphocyte and plasma cell. Case 1 - Figure 8 Very close evaluation shows that the infiltrating oval cells have bland nuclei with some nuclear folding, pale eosinophilic cytoplasm and no mitoses. Case 1 - Figure 9 Very close evaluation shows that the infiltrating oval cells have bland nuclei with some nuclear folding, pale eosinophilic cytoplasm and no mitoses. Microscopic findings Several biopsy fragments show expansion of the lamina propria with a mixture of oval to somewhat spindle shaped cells and eosinophils. The oval cells show bland, uniform nuclei with inconspicuous nucleoli; some are indented, resembling histiocyte nuclei. Their cytoplasm is pale and eosinophilic. In the affected areas, crypt dropout is evident, and remaining crypts show architectural disorder with branching and shortened crypts. Acid fast, PASd, and Giemsa stains were negative for organisms, and did not highlight the ovoid cells. Immunohistochemical stains show that the ovoid cells stain express CD68, but not CD1a, S-100, or HMB-45. Additional stains were obtained, and demonstrated that the ovoid cells stain with CD117 (c-kit), tryptase, CD25, very faintly for CD35, but not with CD21 or CD2. Differential diagnosis The differential diagnosis includes inflammatory and malignant conditions. Entities that might be considered in the differential include microscopic colitis, parasitic infection, hypersensitivity, inflammatory bowel disease, Langerhans cell histiocytosis, involvement by Hodgkin's disease, involvement by monocytic leukemia or other lymphoproliferative disorder, or melanoma. Microscopic colitis typically presents with diarrhea and no obvious colonoscopic findings, as in this case. However, the inflammatory component in microscopic colitis is lymphoplasmacytic, and architectural distortion is usually minimal. Parasitic infection and hypersensitivity reactions often show eosinophilia, but the infiltration of oval cells is unusual and difficult to explain by either of these entities. Inflammatory bowel disease presents with diarrhea, but the absence of colonoscopic findings would be unusual. Some patients with IBD have numerous eosinophils and the oval cell infiltration in this case may be interpreted as "granulomatoid" inflammation suggestive of Crohn's disease. However, the oval cells are not truly forming granulomas and have a rather infiltrative appearance that suggests a neoplastic process rather than usual Crohn's disease. Langerhans cell histiocytosis would certainly be in the differential diagnosis given the histiocytic appearance to the oval cells and the eosinophils. However, LCH is more common in children and presents with ulcerating nodules. The oval cells in this case lack the classic folded and grooved appearance of Langerhans cells, and do not stain for CD1a or S-100 protein. Other dendritic cell proliferations are usually not associated with eosinophils, and are excluded by the immunohistochemistry results. The mixed inflammatory appearance of the infiltrate might raise a question of Hodgkin's disease. Primary Hodgkin's lymphoma of the bowel is extremely rare, and GI involvement in patients with known Hodgkin's disease is seen in less than 10% of cases. No Reed-Sternberg cells are present in this case. Involvement by monocytic leukemia or other lymphoproliferative disorder would certainly enter into the differential diagnosis. However, the oval cell infiltrate is very bland and lacks mitotic figures, arguing against these possibilities. Melanoma can infiltrate the colonic mucosa in this manner, although the eosinophilia would not be explained easily. The absence of pigment, prominent nucleoli, nuclear inclusions, nuclear atypicality, or mitoses, while helpful, does not absolutely exclude melanoma. However, add to that the negative stains for S100 and HMB45 and melanoma can be excluded from the list of possibilities. Diagnosis Involvement by Systemic Mastocytosis Introduction Mast cells are hematopoietic cells that reside in numerous organs and store vasoactive and immunoregulatory mediators including histamine, heparin, proteases such as tryptase, and cytokines. [22] Several of these mediators are released in response to aggregation of the IgE receptor, activation of complement receptors, or by cytokines. Others, such as tryptase, are secreted both constitutively and upon activation. [22] Tryptase is a potent growth factor for epithelial cells, airway smooth muscle cells, and fibroblasts. [17] The most important activating cytokine is mast cell growth factor or stem cell factor (SCF), a Kit ligand, which induces the development of mast cells from progenitor cells. [23] "Gain of function" mutations of Kit are associated with enhanced survival of mast cells and their progenitors. [22] Mast cells are normally found in the gastrointestinal tract, where they play a role in nematode expulsion and allergic disease. [18] Mucosal mast cells increase dramatically in response to immune stimuli, whereas submucosal mast cells are more static and are unrelated to the immune system. [12] In nematode infection, mast cells recruited into the mucosa disrupt epithelial barrier function leading to the influx of solutes and water into the lumen, potentially aiding in the expulsion of the parasite. [18] Autopsy studies have shown that within the mucosa, they form a band superior to the muscularis mucosae and are also distributed randomly throughout the lamina propria whereas in the submucosa they are found around small blood vessels and also distant from vessels. [16] They are more numerous in the mucosa of the ileum, stomach, and duodenum; they number approximately 7 to 17 per hpf. [12, 16] They may play a role in various gastrointestinal diseases such as inflammatory bowel disease, chronic intractable diarrhea, celiac disease, collagenous colitis, and food allergy, although none of these associations is established or without controversy. [7, 12, 15] Reports describe increased mucosal mast cells in some of these disorders although a recent report found no statistical difference in mast cell numbers between normal controls and patients with these various diseases. [11] Interestingly, in this study, patients with parasitic infection (Strongyloides and enterobiasis) had mucosal mast cell numbers that were significantly higher than control patients. Mastocytosis Mastocytosis is defined as a pathologic accumulation of mast cells in various tissues. The disease ranges from a purely dermatologic one that frequently affects children to aggressive mast cell neoplasms such as mast cell leukemia. The following is a classification of mast cell disorders. Category Diagnostic features Prognosis Cutaneous mastocytosis • Lack of systemic involvement • Generally < 2 yrs of age Good Indolent systemic mastocytosis • Lack of advanced categories of mastocytosis • Generally > 2 yrs of age • Often accompanied by skin lesions Good SM associated with clonal hematologic non-mast-cell lineage disease • Commonly associated with MDS or MPD Same as the non-mast-cell disease Aggressive SM • End organ dysfunction due to mast cell infiltration Poor Mast cell leukemia • Mast cells with high grade morphology • > 10% mast cells in peripheral blood or > 20% in bone marrow Poor Mast cell sarcoma • Destructive soft tissue tumor • Mast cells with high grade morphology Poor Extracutaneous mastocytoma • Benign tumor of mature mast cells Good Molecular pathology Unlike cutaneous mastocytosis, systemic mastocytosis (SM) is a clonal disorder, and somatic point mutations of the c-kit gene at codon 816 (usually Asp816Val [D816V]) are found in > 80% of patients with SM. [22] This mutation results in ligand-independent activation and constitutive autophosphorylation of Kit. The fact that the mutation can be detected in monocytes and B cells in peripheral blood indicates that SM involves a hematopoietic progenitor cell and is now accepted as a myeloproliferative disorder. This mutation is not detected in most patients with pediatric-onset cutaneous mastocytosis. In patients with more aggressive subtypes of mast cell disease, the D816V mutation is accompanied by additional genetic changes that confer the mast cells with increased proliferative capacity. Detection of the mutation is enhanced when samples rich in mast cells (bone marrow, skin) are examined. Kit is expressed on hematopoietic stem cells and progenitor cells. It normally is downregulated as progenitor cells mature into fully differentiated forms. The exception to this rule is mast cells, in which Kit is expressed at high levels since is important for a number of mast cell functions such as survival, differentiation, chemotaxis, and activation. Activating c-kit mutations are found in GISTs, germ cell tumors, hematopoietic neoplasms, and mastocytosis. The mutations tend to occur at different sites in different neoplastic conditions. [2] Mutations in the tyrosine kinase domain of c-kit confer resistance to imatinib by interfering with the binding of the drug to the Kit. [2, 14] Newer conformation-tolerant tyrosine kinase inhibitors inhibit D816V c-kit autophosphorylation as well as survival of mast cells carrying this mutation. [1] A variant of SM is associated with clonal eosinophilia, and is known as SM-chronic eosinophilic leukemia. SM-CEL is associated with fusion of the PDGFRA gene to the centromeric FIP1L1 and is sensitive to imatinib. [21] Diagnosis The diagnosis of SM rests on one major and four minor criteria; patients should meet one major and one minor criterion, or three minor criteria. The major criterion consists of the presence of dense infiltrates of mast cells (> 15 mast cells) in bone marrow or other extracutaneous site. Eosinophils often accompany the mast cells in these lesions. The minor criteria are: (a) atypical mast cell morphology (spindling, cytoplasmic projections, and hypogranulation), (b) aberrant mast cell immunophenotype, (c) serum/plasma tryptase level greater than 20 ng/ml (normal around 5 ng/ml), and (d) a codon 816 c-kit mutation in peripheral blood, bone marrow, or lesional tissue. Under normal conditions, mast cells can be detected by staining with antibodies against CD117 (c-kit), mast cell tryptase, and in the case of immature mast cell progenitors CD34 and CD13. [23] Aberrant immunophenotype refers to the fact that mast cells in patients with indolent SM express CD2, CD25, and CD35. CD25 is the most sensitive of these. [22] The clinical diagnosis of SM can be difficult since many of the symptoms are nonspecific and easily confused with other conditions of endocrine, cardiac, allergic, or gastrointestinal type. [23] Skin lesions are typically seen in more indolent variants but may be absent in 20 to 50% of patients, particularly those with aggressive subtypes, making the diagnosis even more challenging. [1, 5, 23] The symptoms of SM are related to mediator release and range from mild to even life threatening. These include episodic flushing, anaphylaxis, lightheadedness, syncope, tachycardia, nausea, vomiting, dyspepsia, diarrhea, abdominal pain, musculoskeletal pain, or hypotension. [1, 3] Gastrointestinal manifestations of mastocytosis A variety of gastrointestinal complaints have been recorded in patients with mastocytosis, including diarrhea, nausea and vomiting, abdominal pain, malabsorption, and hemorrhage; many of these symptoms can be mistaken for other more common GI diseases such as celiac disease or Crohn's disease. [5] These symptoms have been attributed to the release of mast cell contents such as histamine, leukotrienes, proteases, and heparin; overproduction of prostaglandin D2; or direct organ infiltration by mast cells. [4, 5, 9] The exact incidence of GI complaints in SM is unclear, but about half of patients experience some type of GI disturbance. [4, 13] In one series, 81% of patients had GI complaints. [9] The most frequent symptom is abdominal pain, which can be either dyspeptic in nature (epigastric, relieved by antacids or histamine H2 blockers) or non-dyspeptic (lower abdominal in location, cramping in nature, and not relieved by antacids or histamine H2 blockers). [9] Patients with dyspeptic abdominal pain often have gastric acid hypersecretion and endoscopic evidence of duodenitis, duodenal ulcers, or prepyloric ulcers. [4, 9] In fact, peptic ulcer disease is reported in about 24% of these patients. [15] Because 85-100% of patients with SM have increased histamine production, most patients with SM might be expected to have some degree of gastric acid hypersecretion. However, while basal acid output is often elevated in these patients, [4] that is not a universal finding and some patients have normal or even decreased BAO. [4, 13] In one study, serum histamine levels were found to be normal in 4 patients, but histamine content in gastric biopsies was markedly elevated in the 3 cases studied. [4] Maximal acid output – a reflection of parietal cell mass – is not elevated in these patients, indicating that the elevated acid secretion in SM is due to histamine stimulation of normal numbers of parietal cells and that histamine is not trophic to parietal cells. [15] Diarrhea is also a frequent complaint among patients with SM, occurring in 63% of patients in one series [9] (mean 43%). In the study by Cherner et al, diarrhea correlated with gastric hypersecretion but not steatorrhea, suggesting that the mechanism of diarrhea was related to gastric acid hypersecretion and not malabsorption. [9] Gastric hyperacidity causes diarrhea by precipitating bile acids, inactivating pancreatic enzymes, and directly affecting the small intestinal villi. [13] Other possible mechanisms of diarrhea are overproduction of prostaglandin D2 (PGD2), increased levels of other mast cell peptides causing the release of GI peptides such as VIP, alterations in intestinal transit time, and direct involvement of the intestine by SM. [13] However, no studies have correlated involvement of either the small intestine, colon, or rectum with diarrhea; levels of various GI related peptides in patients with SM have not been significantly elevated; and transit time alterations have been inconsistent in various studies. [13] Malabsorption occurs in about 31% of patients with SM, manifested by steatorrhea and impaired absorption of D-xylose (which measures the absorptive function of the upper small intestine) and vitamin B12 (low Schilling test). [4, 9] The mechanism has been attributed to diffuse small intestinal dysfunction related to gastric hypersecretion, inflammatory infiltrates, small bowel injury caused by SM, an associated gluten sensitivity enteropathy, or alteration in small intestinal motility. [13] Pathology in the GI tract Esophageal pathology in SM includes esophagitis and strictures (likely peptic related) or varices due to hepatic involvement. Gastric and duodenal pathology includes peptic ulcer disease, urticarial lesions, thickened folds, and nodular mucosa. Colorectal pathology includes urticarial lesions, polypoid lesions, and intestinal telangiectasia. [5] Most reports describe variable injury (such as villous blunting, crypt dropout) and increased mast cells in the mucosa and/or submucosa in SM relative to normal mucosa. [5, 6, 8, 10, 11] Increased eosinophils are frequently noted. [8, 11] In some cases, colonic or rectal mucosal biopsies show massive infiltrates of mast cells and eosinophils. [5, 11, 20] The mast cells are frequently described as uniform cells with oval or indented nuclei, inconspicuous nucleoli, and pale cytoplasm. [5] Conversely, some series report no increased mast cells in the GI mucosa of patients with SM. [4, 19] The number of mast cells is not related to symptoms, and appears to be patchy throughout the intestine. [11, 15] A recent report describes variable findings from minimal changes by HE examination to marked expansion of the lamina propria by mixed infiltrates of CD25 positive mast cells, eosinophils, lymphocytes, and plasma cells. [11] The authors note in this study that gastric biopsies may show less involvement relative to the small or large intestine. Mast cells can be identified through a variety of means. Although Giemsa or toluidine blue stains highlight mast cells, immunohistochemistry using antibodies directed against c-kit or mast cell tryptase is more sensitive, particularly in the setting of neoplastic hypogranulated mast cells. The neoplastic nature of the mast cells can be confirmed with by their aberrant staining for CD25 and CD2. In a recent report, CD25 immunostaining proved useful to distinguish neoplastic mast cell infiltration in SM from reactive mast cell infiltrates such as in parasitic infection or other inflammatory disorders. [11] Treatment The treatment of SM involves controlling symptoms due to mediator release from mast cells, and reducing mast cell burden. [3] H1 antihistamines are used to control pruritus whereas H2 antihistamines are to counteract symptoms related to gastric hypersecretion, such as dyspeptic pain, diarrhea, or malabsorption. [13] Omeprazole may be a more potent alternative to counteract acidity but H2 blockers also have the benefit of controlling other symptoms related to hyperhistinemia. Cromolyn sodium stabilizes the mast cell membrane and may be beneficial for GI symptoms including diarrhea, abdominal pain, nausea, and vomiting. Therapies which may reduce mast cell burden include interferon-alpha [20] and 2 chlorodeoxyadenosine. These are typically reserved for patients with more aggressive subtypes of mast cell disease. Despite the mutation in Kit, imatinib mesylate (Gleevec) has no effect on SM since it fails to inhibit Kit bearing codon 816 mutations. References Akin C: Molecular diagnosis of mast cell disorders: a paper from the 2005 William Beaumont Hospital Symposium on Molecular Pathology. Journal of Molecular Diagnostics. 2006; 8:412-9. Akin C, Metcalfe DD: The biology of Kit in disease and the application of pharmacogenetics. Journal of Allergy & Clinical Immunology. 2004; 114:13-9; quiz 20. Akin C, Metcalfe DD: Systemic mastocytosis. Annu Rev Med. 2004; 55:419-32. Ammann RW, Vetter D, Deyhle P, et al.: Gastrointestinal involvement in systemic mastocytosis. Gut. 1976; 17:107-12. 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