I. Granulomatous pattern:     Images:        

1.Tuberculoid granuloma: Tuberculosis ,  tuberculoid leprosy , syphilis ,  cryptococcus .      Image  ;  Image     

2.Suppurative granuloma: Image  Atypical Mycobacterial Infection , lymphogranuloma venereum , blastomycosis-like pyoderma.  

3. Palisading granuloma: Phaeohyphomycosis, Cryptococcosis , coccidioidomycosis , mycobacteriosis.    Image1 ; Image2

4. Histiocytic granuloma: Infection atypical mycobacteria , lepromatous  leprosy ,  malakoplakia  Image , leishmaniasis.   Image Link1 ; Image Link2 ; Image Link3 .

2.Type of inflammatory cellular infiltrate:            
1. Prominence of plasma cells:  Syphilis  Image1 ; Image2 , Chancroid , lymphogranuloma venereum .
2. Prominence of eosinophils: Arthropod bite, helminth infestation. Image
3. Prominence of neutrophils: Impetigo , Granuloma Inguinale , erysipelas, erythema nodosum leprosum, blastomycosis - like pyoderma, chancroid , mycetoma , actinomycosis , phaeohyphomycosis , mucormycosis etc.
4. Presence of histiocytes and plasma cells:  Rhinoscleroma , syphilis , granuloma inguinale.

3.Presence of parasitized macrophages and parasitized multinucleated giant cells:

-Parasitized macrophages: Rhinoscleroma  Image Link1 ; Image Link2 Image Link3 , Lepromatous leprosy  Image, toxoplasmosis , histoplasmosis, leishmaniasis .

-Parasitized multinucleated giant cells: fungal infection .

4. Changes in the epidermis:     Image
1. Psoriasiform epidermal hyperplasia: Chronic candidosis Image
2. Pseudoepitheliomatous hyperplasia: Amoebiasis , toxoplasmosis  , blastomycosis-like pyoderma, tuberculosis , human papilloma virus infections , verrucous herpes/ varicella lesions in HIV infection.
3. Epidermal spongiosis:   Dermatophytoses , candidosis , viral infection, cutaneous larva migrans , arthropod bites , cercarial dermatitis.
4. Intraepidermal vesiculation:  Herpes Simplex Virus Infection , Herpes Zoster Virus , varicella. These are characterized by intranuclear inclusions and ballooning degeneration. Image1 ;  Image2 .

5. Changes in the dermis and cutaneous appendages:    Image
1.Superficial and deep dermal perivascular inflammatory infiltrate Image ; Image ; Arthropod bite (eosinophils are noted) Image, leprosy , secondary syphilis (lymphoplasmacytic infiltrate)
2. Folliculitis and perifolliculitis: Image , Dermatophytoses , pityrosporum folliculitis,  syphilis Image1 ; Image2 , demodex infestation, pyogenic bacterial infection.
3. Vasculitis: Necrotizing fasciitis, erythema nodosum leprosum, meningococcal and gonococcal septicemia, rickettsial infections, cytomegalovirus infection, recurrent herpes.                        
4.Tissue necrosis:  Cat Scratch Disease, ecthyma gangrenosum, Mycobacterium ulcerans Infection , necrotizing fasciitis, diphtheria .

6. Spindle cell pseudotumour: Histoid leprosy Image,  atypical mycobacteria.

7. Invisible dermatoses:  Section appears almost  normal when stained with H&E.  Dermatophytoses   Image1 ;  Image2  ; Image3 ; Image4   ; Pityriasis versicolor Image   ;  Erythrasma.

Identification of fungi in tissue section:

- PAS with or without diastase is the most commonly used special stain. Cell wall stains purple with PAS. Cryptococcus is stained with mucicarmine stain or a combined alcian blue-PAS stain. The cell wall and the  capsule appear in contrasting colour.

- Silver methenamine stain (Grocott's method) . Stains fungi  black against green backround. It is more reliable than PAS  for detecting degenerate fungal organisms.           

- Gomori methenamine silver with H&E counterstain demonstrate fungi and tissue components simultaneously.

- Calcofluor white used to stain frozen or paraffin sections and viewed with a fluorescence  microscope.

- Autofluorescent fungi include Blastomyces, Cryptococcus, Candida, Aspergillus , Coccidioides and sometimes Histoplasma.

- Polymerase chain reaction (PCR) technique :  Used to identify specific species of fungi.

Histochemistry in identification of microorganisms in skin sections:

- Pyodermas (impetigo and its variants and ecthyma) - Cocci demonstrated by Gram's stain

- Erythrasma -small coccobacilli in stratum corneum- Gram' stain, PAS and methenamine silver  positive.

-Tuberculosis and non- tuberculous (atypical ) mycobacterial. Acid fast bacilli identified by Ziehl Neelsen stain. 

- Leprosy- Hematoxylin-eosin and Fite Faraco staining method on tissue section are sufficient for evaluation. Sometimes Gomori methenamine silver stain help to detect remnants of M. Leprae in treated patients.

- Histoid leprosy - Acid fast bacilli  arranged parallel to  long axis of cell.

- Granuloma inguinale & Chancroid- Gram negative bacilli- Demonstrated by  Warthin Starry (silver) and Giemsa stain

- Rhinoscleroma- PAS, Grams's & Warthin starry stains positive.

- Malakoplakia- PAS positive diastase resistant inclusions. Calcospherites  (MG bodies) are Von Kossa -positive.

- Rickettsia- Organisms demonstrated in endothelium or vessel wall using fluorescein-labelled antisera or with immunoperoxidase techniques.

- Spirochaete-Treponema pallidum and its subspecies are demonstrated by silver impregnation technique -  Levaditi or Warthin-Starry.

- Actinomycosis -  Granules are composed of slender filaments - Gram's & PAS positive & stains grey or black with silver methenamine. Not acid fast.
Club shaped bodies at the periphery & matrix of granules are Gram negative.

- Nocardiosis- Gram positive & weakly acid fast. Also stains with silver methenamine.

- Leishmaniasis-  Leishman-Donovan bodies are better identified in sections stained with Weigert iron hematoxylin than those stained with hematoxylin and eosin or the Giemsa stain.