The mainstay of dermatopathology is the examination of skin biopsies after fixation in formalin, embedding in paraffin, and staining with hematoxylin and eosin (H&E). This technique has been quite durable in the history of histopathology because it offers many advantages: it is relatively quick, inexpensive, suitable for most practical needs, and relatively easy to master. However, it cannot answer all the questions that a case may pose at the diagnostic level. Therefore, pathologists have always searched for additional methods to analyze their histologic material.
There is an extensive battery of “special” stains listed in texts discussing histologic techniques.1,2 Few of them are of practical value for diagnostic dermatopathologists. A synopsis of some of the stains that appear relevant for a modern dermatopathology laboratory is listed in Table A1-1.
TABLE A1-1Common Special Stains in Dermatopathology ||Download (.pdf) TABLE A1-1 Common Special Stains in Dermatopathology
|STAIN ||APPLICATION ||RESULTS |
|H&E ||Routine ||Nuclei: blue; cytoplasm; red |
|Collagen, muscles, nerves: red |
|PAS/diastase ||Fungi, parasites ||Wall of organisms: red |
|Glycogen (eg, in trichilemmoma) ||Glycogen: red on PAS; clear after diastase digestion |
|Basement membrane thickening (eg, LE) ||Basement membrane: pink/red |
|Cryoglobulinemia ||Cryoprecipitates: bright red |
|Mucicarmine ||Adenocarcinomas, ||Mucin: red |
|Cryptococcus ||Capsule: red |
|Toluidine blue ||Mast cells ||Metachromatically purple |
|Giemsa ||Mast cells ||Metachromatically purple |
|Leishmania ||Blue |
|Masson’s trichrome ||Fibrosis ||Collagen: green; nuclei, muscle: dark red |
|Infantile digital fibromatosis ||Hyaline globules: red |
|Van Gieson ||Arterial injury ||Elastic fibers: black |
|Van Kossa ||Calcium ||Black |
|Congo red ||Amyloid ||Green under polarized light |
|Fontana ||Melanin ||Black |
|Prussian blue ||Hemosiderin/iron ||Blue |
|Gram stain ||Bacteria ||Depending on method used (gram positive: usually blue; gram negative: usually red) |
|Methenamine-silver ||Fungi, parasites ||Black |
|Dieterle/Steiner/ ||Spirochetes, ||Black |
|Warthin-Starry ||Rochalimaea ||Black |
|AFB/Fite ||Acid-fast bacilli ||Red |
Stains for microorganisms
Perhaps the most important of all the special stains in the practice of dermatopathology are stains that help to identify microorganisms. This includes the modifications of the Gram stain, such as by Brown and Hopp, for most bacterial organisms; the methenamine silver stain or periodic acid-Schiff (PAS) stain for fungi and parasites; and the Ziehl-Neelson or Fite stain for acid-fast bacilli. Silver stains, such as according to Dieterle, Warthin-Starry, and Steiner, are commonly used to identify spirochetes (syphilis, Lyme disease) and the organisms in cat-scratch disease and bacillary angiomatosis (Rochalimaea). Leishmania is best identified by a Giemsa stain.
Periodic acid-Schiff stain
This stain demonstrates mucosubstances, basement membrane material, fibrinoid material, and glycogen in a specific fashion when combined with diastase digestion. The staining reaction yields a pink to red color. An intensely bright red homogeneous material within vessels suggests cryoglobulins. The PAS stain is also useful in highlighting most types of fungi and parasites.