Demonstration of Charcot-Leyden Crystals in Eosinophilic Cystitis

Abstract

To the Editor.—The presence and diagnostic relevance of Charcot-Leyden crystals (CLCs) in eosinophilic cystitis (EC) was reported in detail recently.1 Although their association with the disease is well established, CLCs are still poorly studied.2–4 Appreciation of CLCs on standard hematoxylin-eosin–stained tissue sections is not always straightforward, especially with the background of apoptotic changes accompanied by different degrees of necrosis seen in the acute phase of EC.1,5 The CLCs stain faintly with eosin and do not polarize on examination under polarized light microscopy.Chemical knowledge of CLCs was limited until 1980 when it was discovered that they contain cationic proteins that stain satisfactorily with hematoxylin-basic fuchsin-picric acid in brilliant dark-pink coloration.2Charcot-Leyden crystals consist of a 13 000–molecular weight acidic protein whose amino acid composition distinguished it from the 9300–molecular weight major basic protein, the principal constituent of eosinophil large granules; this protein is identical to lysophospholipase3 and is stained by basic fuchsin in the Ziehl-Neelsen method.We suggest 2 helpful although not so popular diagnostic methods—autofluorescence and acid-fast stain—for easy detection of CLCs.6,7We performed a study on the incidence of CLCs in EC focusing precisely on these 2 diagnostic features (autofluorescence and acid-fast stain) comparing them with standard hematoxylin-eosin–stained tissue sections. Our study examined 15 cases with EC. On our hematoxylin-eosin–stained sections (Ref. No. 676500; Thermo Scientific Shandon, Pittsburgh, Pennsylvania), CLCs were readily seen in only 4 of 15 cases (Figure, a). The CLCs stained red with Ziehl-Neelsen (Ref. No. 1.09215.0500; Merck, Darmstadt, Germany) in 6 of 15 cases and exhibited yellow-green autofluorescence (8 of 15 cases) when formalin-fixed, paraffin-embedded, hematoxylin-eosin–stained sections were viewed with fluorescent microscope (Zeiss) with an IVFI condenser using filters FT 510 and LP 520 (Figure, b and c). Moreover, fluorescence made detection of CLCs fast and easy especially in hypercellular areas versus the time-consuming screening for them with conventional light microscopy. The remaining Ziehl-Neelsen–negative and fluorescence-negative cases presented with a severe degree of necrosis, which in our opinion was the reason for dye impermeability and noninformative fluorescence.Although formalin-induced autofluorescence and acid-fast stain of CLCs are probably nonspecific phenomena, use of the fluorescent microscope and the Ziehl-Neelsen stain can successfully help in the diagnosis of acute-phase EC, especially in samples with massive tissue necrosis.