Cytochemistry
Special stains and cytochemical techniques are particularly useful as adjuvants in the diagnosis of lymph node lesions by identifying various biochemical and enzymatic cell markers (Table 5.1).
Periodic Acid–Schiff Stain
Periodic acid–Schiff (PAS) stains glycogen (1) as block-like, intracytoplasmic aggregates in some acute lymphoblastic leukemia cells or as a chunk-like necklace in erythroleukemia cells. Adding diastase (or amylase) removes glycogen. Periodic acid–Schiff with diastase identifies the carbohydrate portion of intracytoplasmic immunoglobulins in plasma cells and plasmacytoid lymphocytes (2). Immunoglobulin A (IgA) myeloma cells are intensely red because IgA contains a higher percentage of carbohydrate than either IgM or IgG; they are called flame cells. Periodic acid–Schiff with diastase (or amylase) also strongly stains immunoglobulin deposits, such as Russell bodies and Dutcher bodies, and an interstitial amorphous substance (frequently containing immunoglobulin) that is found in some types of lymphomas and angioimmunoblastic lymphadenopathy with dysproteinemia. Periodic acid–Schiff with diastase is useful in differentiating intensely red-staining megakaryocytes from negative Reed-Sternberg cells (3).
Methyl Green Pyronine Stain
Methyl green pyronine stain can be used in the differential diagnosis of lymphoma versus plasmacytoma/multiple myeloma. Plasma cells and plasmacytoid cells secreting immunoglobulin and immunoblasts contain more RNA (intracytoplasmic pyroninophilic material) than do mature B-lymphoma cells expressing surface immunoglobulin (4) (Fig. 5.1). Methyl green pyronin is also useful in distinguishing Burkitt lymphoma (abundant RNA) from lymphoblastic lymphoma (scant RNA) (5). Acid decalcification, incomplete fixation, or tissue necrosis can degrade RNA.
Reticulin Staining By Silver Impregnation
Several methods of reticulin staining by silver impregnation are available (6). The reticulin fibrillar framework of lymphoid tissues becomes apparent and serves as a useful criterion to distinguish large-cell (histiocytic) lymphomas from metastatic undifferentiated carcinomas or melanomas. A well-developed, fine, branching reticulin network with pericellular fibrils is generally characteristic of lymphomas, whereas thick reticulin and collagen fibers with an alveolar pattern surrounding nests and cords of cells are indicative of metastatic nonlymphoid tumors (Fig. 1.30).
Sudan Black B
Sudan black B (SBB) is useful in differentiating acute myeloid, lymphoid, and myelomonocytic leukemias (7). Sudan black B staining parallels peroxidase activity; it is strong in myeloid cells and eosinophils, faint in monocytes, and absent in normoblasts and lymphocytes, although rare lymphoblasts contain SBB-positive granules (8). Myeloid cells, from myeloblasts to neutrophils, show increasing sudanophilia as the number of granules increases (Fig. 5.2). Auer bodies are intensely sudanophilic. In contrast to peroxidase enzyme activity, staining with SBB does not diminish within granules in older, light-exposed smears (9).
Peroxidase Reaction
Peroxidase reaction is positive in neutrophilic and eosinophilic series (10) and faintly positive in monocytes (11). It can be used to differentiate these from peroxidase-negative lymphoid and erythroid cells (7) (Fig. 5.3).
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