Isolated bone marrow mastocytosis

Isolated bone marrow mastocytosis (also known as bone marrow mastocytosis or isolated medullary mastocytosis) is a rare subtype of systemic mastocytosis characterized by the abnormal accumulation of mast cells exclusively within the bone marrow, without significant involvement of other organs such as the skin. Mast cells are immune cells normally involved in allergic responses and inflammation, but in this condition they proliferate abnormally and can release excessive amounts of chemical mediators including histamine, tryptase, and other bioactive substances. The disease primarily affects the hematologic system, and patients may present with elevated serum tryptase levels, which serves as an important diagnostic biomarker. Clinical manifestations can vary considerably. Many patients experience symptoms related to mast cell mediator release, including flushing, gastrointestinal complaints (such as abdominal pain, diarrhea, and nausea), episodes of hypotension, and anaphylaxis-like reactions. Some patients may also develop osteoporosis or osteopenia due to the effects of mast cell infiltration and mediator release on bone metabolism. Importantly, unlike other forms of mastocytosis, patients with isolated bone marrow mastocytosis lack the characteristic skin lesions (urticaria pigmentosa) seen in cutaneous or typical systemic mastocytosis, which can make initial diagnosis more challenging. Diagnosis is established through bone marrow biopsy demonstrating multifocal dense aggregates of mast cells, often with aberrant expression of CD25 and/or CD2 on mast cells, and frequently associated with the KIT D816V somatic mutation. Treatment is primarily directed at controlling mediator-related symptoms using antihistamines (both H1 and H2 blockers), mast cell stabilizers, and leukotriene antagonists. For patients with osteoporosis, bisphosphonates or other bone-protective agents may be indicated. In cases with more aggressive features, targeted therapies such as midostaurin or avapritinib, which inhibit KIT signaling, may be considered. Regular monitoring of serum tryptase levels and bone marrow status is recommended to assess disease stability or progression.

Inheritance

Sporadic

Usually appears on its own, not inherited from a parent

Age of Onset

Adult

Begins in adulthood (age 18 or older)

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