Medical terms, defined.

A leukoerythroblastic reaction is the presence of immature white blood cells (myelocytes, metamyelocytes) and nucleated red blood cells in the peripheral blood, along with teardrop-shaped RBCs (dacrocytes). It typically indicates bone ma...

Granulocyte-colony stimulating factor (G-CSF, e.g., filgrastim) is a glycoprotein growth factor that stimulates bone marrow production of neutrophils. It's used clinically to treat chemotherapy-induced neutropenia and to mobilize hematop...

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a cytokine that stimulates proliferation and differentiation of granulocyte and monocyte/macrophage progenitor cells in the bone marrow. It is used clinically (e.g., sargramost...

Poikilocytosis refers to the presence of abnormally shaped red blood cells (poikilocytes) in peripheral blood, distinct from anisocytosis (abnormal size variation). It is a nonspecific finding seen on peripheral smear that points toward...

Anisocytosis refers to abnormal variation in the size of red blood cells (RBCs), observed on peripheral blood smear. It is quantified by the RBC distribution width (RDW) on a CBC and is a nonspecific finding seen in many anemias. It indi...

HbA2 is a minor normal hemoglobin variant composed of two alpha and two delta globin chains (α2δ2), normally comprising 2-3.5% of total adult hemoglobin. It is clinically significant because its elevation is a key diagnostic marker for b...

Tryptase is a serine protease stored in mast cell granules and released upon mast cell degranulation. Serum tryptase levels are used clinically as a marker of systemic mastocytosis and anaphylaxis, as it remains elevated longer than hist...

Sargramostim is recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF) used to stimulate bone marrow recovery after chemotherapy, radiation exposure, or stem cell transplantation. It promotes proliferation and differ...

The reticulate body (RB) is the intracellular, metabolically active, replicating form of Chlamydia species (e.g., Chlamydia trachomatis, Chlamydophila pneumoniae). It exists within host cell inclusions and divides by binary fission, late...

Reassortment is the exchange of genetic segments between different strains of segmented RNA viruses (notably influenza) when two different strains co-infect the same host cell. This process can produce novel viral strains with new antige...

DMSA (dimercaptosuccinic acid) is used in two main contexts on boards: as a chelating agent for heavy metal (lead/arsenic/mercury) poisoning, and as a radiolabeled tracer (Tc-99m DMSA scan) for renal cortical imaging to detect scarring o...

A xenograft (heterograft) is a tissue or organ graft transplanted between different species, such as porcine heart valves used in humans. It carries the highest immunologic rejection risk among graft types due to major antigenic differen...

Succimer (DMSA) is an oral heavy metal chelator used primarily for treatment of lead poisoning in children, especially when blood lead levels are elevated but the patient does not require IV therapy. It works by chelating lead (and other...

Pautrier microabscesses are collections of neoplastic T-lymphocytes (cerebriform mononuclear cells) within the epidermis, a characteristic histologic finding in mycosis fungoides, the most common form of cutaneous T-cell lymphoma (CTCL)....

Hyperacute transplant rejection occurs within minutes to hours after transplantation due to preexisting host antibodies against donor antigens (ABO blood group or HLA Class I). It causes widespread microvascular thrombosis and graft necr...

The mantle zone is the thin rim of small, resting naïve B lymphocytes surrounding the germinal center of a secondary lymphoid follicle. It expresses CD5, CD20, and cyclin D1 (in neoplastic transformation), and is clinically significant a...

BCL-6 (B-cell lymphoma 6) is a transcriptional repressor essential for formation and maintenance of germinal centers in lymph nodes. It is used as an immunohistochemical marker for germinal center B-cell origin and is implicated in sever...

Richter transformation refers to the transformation of chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL) into an aggressive lymphoma, most commonly diffuse large B-cell lymphoma (DLBCL). It occurs in approximately 2-...

Indolent describes a disease process that progresses slowly, causes minimal symptoms, and typically has a favorable or protracted clinical course. It is commonly used to describe certain cancers (e.g., follicular lymphoma, CLL) and chron...

Cyclin D1 is a key regulatory protein that controls the G1 to S phase transition of the cell cycle by activating cyclin-dependent kinases 4 and 6 (CDK4/6). It is overexpressed in several malignancies, most notably mantle cell lymphoma, d...

Non-contiguous refers to lesions, skip lesions, or anatomical involvement that is not continuous or adjacent, with intervening areas of normal tissue. This term is classically used to describe the pattern of bowel involvement in Crohn's...

Tingible body macrophages are large phagocytic cells found in the germinal centers of lymphoid follicles that engulf apoptotic B cells undergoing negative selection. Their abundant basophilic, nuclear debris-filled cytoplasm creates a ch...

In medicine, 'contiguous' describes structures, tissues, or lesions that are directly adjacent to or touching one another, often implying spread of disease (e.g., infection, tumor) from one structure to the next without intervening gaps.

Finger drop refers to the inability to extend the fingers at the metacarpophalangeal (MCP) joints while wrist extension remains relatively preserved. This is a hallmark finding of posterior interosseous nerve (PIN) syndrome, a pure motor...

Nodular sclerosis is the most common subtype of classic Hodgkin lymphoma, accounting for ~70% of cases. It is characterized by collagen bands dividing lymph nodes into nodules containing lacunar cells (a variant of Reed-Sternberg cells)....

RET is a proto-oncogene encoding a receptor tyrosine kinase for GDNF-family ligands. Germline gain-of-function mutations cause MEN2A, MEN2B, and familial medullary thyroid carcinoma, while loss-of-function mutations/deletions are associa...

BRAF is a proto-oncogene encoding a serine/threonine kinase in the RAS-RAF-MEK-ERK (MAPK) signaling pathway, which regulates cell growth and division. Mutations (most commonly V600E) cause constitutive activation of this pathway, driving...

Basophilic stippling refers to small, dark-blue granules dispersed throughout the cytoplasm of red blood cells on Wright-Giemsa stain, representing aggregated ribosomal RNA/ribosomes. It is classically associated with lead poisoning, but...

Tartrate-resistant acid phosphatase (TRAP) is an enzyme marker used to identify hairy cell leukemia, a rare B-cell malignancy. It distinguishes hairy cell leukemia from other B-cell lymphoproliferative disorders on special staining of pe...

Nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL) is a rare subtype of Hodgkin lymphoma characterized by 'popcorn cells' (lymphocyte-predominant cells, a variant of Reed-Sternberg cells) that are CD20+ and CD15/CD30 negative, disti...

S4 (fourth heart sound) is a low-frequency sound heard just before S1, caused by atrial contraction forcing blood into a stiff, noncompliant ventricle. It is best heard with the bell of the stethoscope at the apex with the patient in lef...

Anti-Tr (also known as anti-DNER, delta/notch-like epidermal growth factor-related receptor) antibodies are associated with paraneoplastic cerebellar degeneration (PCD), most classically linked to Hodgkin lymphoma. They target Purkinje c...

Postherpetic neuralgia (PHN) is chronic neuropathic pain persisting more than 90 days after resolution of a herpes zoster (shingles) rash, caused by reactivation of varicella-zoster virus in sensory ganglia. It most commonly affects the...

CD5 is a cell surface glycoprotein marker found on normal T cells and a small subset of B cells (B1 cells). It is clinically significant as an aberrant marker on malignant B cells in chronic lymphocytic leukemia (CLL) and mantle cell lym...

Myeloblasts are immature, undifferentiated precursor cells of the myeloid lineage found in the bone marrow, giving rise to granulocytes (neutrophils, eosinophils, basophils). They are normally <5% of bone marrow cells; an increased perce...

Anti-Tr antibodies (also called anti-DNER antibodies) are paraneoplastic autoantibodies most classically associated with paraneoplastic cerebellar degeneration (PCD) in patients with Hodgkin lymphoma. They target the DNER (delta/notch-li...

CD20 is a non-glycosylated phosphoprotein expressed on the surface of B lymphocytes from the pre-B cell stage through mature B cells, but not on plasma cells or stem cells. It functions as a calcium channel regulator involved in B cell a...

Eltrombopag is an oral thrombopoietin (TPO) receptor agonist used to stimulate platelet production in conditions like chronic immune thrombocytopenia (ITP), severe aplastic anemia, and thrombocytopenia associated with hepatitis C treatme...

PIGA is an X-linked gene required for synthesis of the glycosylphosphatidylinositol (GPI) anchor, which tethers surface proteins like CD55 and CD59 to blood cell membranes. Acquired somatic mutations in PIGA in a hematopoietic stem cell...

Herpes zoster ophthalmicus (HZO) is reactivation of varicella-zoster virus (VZV) within the ophthalmic division (V1) of the trigeminal nerve, causing a painful vesicular rash on the forehead, eyelid, and periorbital area. Involvement of...

Leukocyte extravasation is the process by which white blood cells exit the bloodstream and migrate into tissue in response to infection or injury. It involves a sequential cascade: rolling, activation, firm adhesion, and transmigration....

Th17 cells are a subset of CD4+ helper T cells that produce IL-17, IL-21, and IL-22, playing a key role in defense against extracellular bacteria and fungi, particularly at mucosal surfaces. They are implicated in the pathogenesis of sev...

Herpes Simplex Virus (HSV) is a double-stranded DNA virus of the Herpesviridae family with two main types: HSV-1 (classically oral/orolabial lesions, gingivostomatitis, herpes labialis) and HSV-2 (classically genital herpes), though both...

Chemotaxis is the directed movement of cells, especially leukocytes, along a chemical gradient toward a site of infection or inflammation. Key chemotactic factors include C5a, IL-8, LTB4, and bacterial N-formylmethionine peptides. Defect...

Transmigration (diapedesis) is the process by which leukocytes squeeze through endothelial cell junctions of post-capillary venules to move from the bloodstream into surrounding tissue during inflammation. It is a key step in the leukocy...

Diapedesis is the process by which leukocytes squeeze through the endothelial cell junctions of postcapillary venules to migrate from the bloodstream into surrounding tissue, typically in response to infection or injury. It is a key step...

Congo red is a histological dye used to detect amyloid deposits in tissue. Under polarized light, amyloid stained with Congo red exhibits characteristic apple-green birefringence, which is pathognomonic for amyloidosis.

Bence Jones proteins are monoclonal free immunoglobulin light chains (kappa or lambda) found in the urine, classically associated with multiple myeloma. They are a key diagnostic marker detected via urine protein electrophoresis (UPEP) a...

Serum Protein Electrophoresis (SPEP) is a lab test that separates serum proteins by electrical charge and size into albumin and globulin fractions (alpha-1, alpha-2, beta, gamma). It is primarily used to detect monoclonal gammopathies (M...

Serum protein electrophoresis (SPEP) is a lab test that separates serum proteins by size and charge into albumin and globulin fractions (alpha-1, alpha-2, beta, gamma) to detect abnormal protein patterns. It is most commonly used to scre...