Blood, Bone Marrow, and Related Disorders
Blood, bone marrow, and related disorders
This domain links marrow structure and function to systemic disease. Aplastic anemia is immune-mediated marrow failure: pancytopenia, reticulocytopenia, and a hypocellular marrow biopsy without fibrosis or malignant infiltration; distinguish it from hypoplastic myelodysplasia (dysplasia, abnormal cytogenetics) and from marrow replacement. Myelophthisis from metastatic carcinoma, fibrosis, granulomas, or storage disease produces a leukoerythroblastic picture - nucleated red cells, teardrop cells, immature myeloid cells - with fibrosis on reticulin stain.
Primary myelofibrosis (or post-polycythemia vera/essential thrombocythemia myelofibrosis) shows collagen fibrosis, osteosclerosis, atypical megakaryocytes, splenomegaly with extramedullary hematopoiesis, and JAK2, CALR, or MPL mutations. Storage diseases include Gaucher disease (crumpled-tissue macrophages, glucocerebrosidase deficiency) and Niemann-Pick disease; sea-blue histiocytes are nonspecific. Marrow examination combines aspirate smears (morphology, iron stain, cytogenetics, flow) with trephine biopsy (cellularity, architecture, fibrosis, immunohistochemistry); touch imprints help when the aspirate is dry.
After transplantation, chimerism testing (STR or SNP) and marrow cellularity guide management; engraftment is defined by sustained neutrophil and platelet recovery. Marrow necrosis with serous fat atrophy suggests severe systemic illness or infarction.
Trap: a dry tap reflects aspirate failure, not necessarily hypocellularity; the biopsy may be packed with fibrosis or tumor. Always obtain a trephine biopsy.
Rule of thumb: leukoerythroblastic smear plus teardrop cells plus splenomegaly means marrow infiltration or fibrosis until the biopsy proves otherwise.