Histopathologic diagnosis of dermatitis
Histopathology of dermatitis can be performed in uncertain cases of inflammatory skin condition that remain uncertain after history and physical examination.
Sampling
Generally a skin biopsy:- For punch biopsies, a size of 4 mm is preferred for most inflammatory dermatoses.
- Panniculitis or cutaneous lymphoproliferative disorders: 6 mm punch biopsy or skin excision.
Fixation
- Generally: Buffered 4% formaldehyde.
- In suspected immunologic disease: Fixation for immunofluorescence, with for example Michel's solution. For details, see immunofluorescense of skin tissues
Staining
- If suspected bacterial and fungal microorganisms, consider Gram stain and Gomori methenamine silver stain.
Microscopic evaluation
- Epidermis, papillary dermis, and superficial vascular plexus:
Non vesicullobullous, non-pustular lesions with epidermal changes
Spongiotic dermatitis
It is characterized by epithelial intercellular edema.In addition to above, an unspecific spongiotic dermatitis can be consistent with nummular dermatitis, dyshidrotic dermatitis, Id reaction, dermatophytosis, miliaria, Gianotti-Crosti syndrome and pityriasis rosea.
Interface dermatitis
These are sorted into either:- Interface dermatitis with vacuolar change
- Interface dermatitis with lichenoid inflammation
Interface dermatitis with vacuolar change
Interface dermatitis with lichenoid inflammation
Interface dermatitis with lichenoid inflammation, not otherwise specified, can be caused by lichen planus-like keratosis, lichenoid actinic keratosis, lichenoid lupus erythematosus, lichenoid GVHD, pigmented purpuric dermatosis, pityriasis rosea, and pityriasis lichenoides chronica. Unusual conditions that can be associated with a lichenoid inflammatory cell infiltrate are HIV dermatitis, syphilis, mycosis fungoides, urticaria pigmentosa, and post-inflammatory hyperpigmentation. In cases of post-inflammatory hyperpigmentation, it is important to exclude potentially harmful mimics such as a regressed melanocytic lesion or lichenoid pigmented actinic keratosis.Psoriaform dermatitis
Examining multiple deeper levels is recommended if initial cuts do not correlate well with the clinical history.Psoriaform dermatitis typically displays:
- Regular epidermal hyperplasia, elongation of the rete ridges, hyperkeratosis, and parakeratosis.
- Usually:A superficial perivascular inflammatory infiltrate
- Often: Thinning of epidermal cells overlying the tips of dermal papillae, and dilated, tortuous blood vessels within these papillae
| Condition | Hyperkeratosis | Parakeratosis | Acanthosis | Suprapapillary plate | Granular cell layer changes | Spinous cell layer changes | Basal cell layer changes | Other distinctive feature | Micrograph | Photograph |
| Psoriasis | Present | Diffuse | Regular | Thin | Decreased or absent | Increased mitoses; minimal spongiosis Clubbed rete pegs | Absent |
| ||
| Psoriasiform drug reaction | Present | Focal | Regular and irregular | Normal or thick | Normal | Spongiosis; eosinophilic infiltrate | Inflammatory cells; Civatte bodies | - | - | |
| Chronic allergic/contact and atopic dermatitis | Present | Focal; crust may be present | Irregular | Normal or thick | Normal | Spongiosis; eosinophilic infiltrate | Absent | - | - | |
| Fungal infection | Compact | Focal; crust may be present | Irregular | Normal or thick | Normal | Occasional neutrophiles; | Absent | - | - | |
| Lichen simplex chronicus | Present | Focal; thick crust | Regular or irregular | Thin or thick | Thickened; hypergranulosis | ±minimal inflammatory infiltrate | Absent | - | - | |
| Scabies | Present | Focal or diffuse | Irregular | Normal or thick | Normal | Inflammatory infiltrate; eosinophilic spongiosis | Absent | - | - | |
| Seborrheic dermatitis and HIV dermatitis | Present | Focal | Irregular | Normal or thick | Normal | Spongiosis; lymphocytic and neutrophilic infiltrate | Absent | - | - | |
| Pityriasis rubra pilaris | Compact | Shoulder parakeratosis; alternating orthokeratosis and parakeratosis | Regular or irregular | Normal or thick | Normal | Spongiosis; lymphocytic infiltrate; rare acantholysis | Occasional vacuolar change | - | - | |
| Pityriasis rosea | Present | Focal | Irregular | Normal or thick | Normal | Small foci of spongiosis; lymphocytic infiltrate | Occasional necrotic keratinocytes | - | - | |
| Syphilis | Present | Focal | Regular or irregular | Normal or thick | Normal | Lymphocytes and neutrophils | Interface change | - | - | |
| Pityriasis lichenoides chronica | Present | Caps of parakeratosis | Irregular | Normal | Normal | Mild spongiosis, lymphocytic infiltrate; necrotic keratinocytes | Necrotic keratinocytes | - | - | |
| Mycosis fungoides | Present | Focal | Regular or irregular | Normal | Normal | Minimal or no spongiosis; ±Pautrier microabscess | Atypical lymphoid cells lining the dermo–epidermal junction | - |
Non vesicullobullous, non-pustular lesions without epidermal changes
Lymphocytic infiltrate
Lymphoeosinophilic infiltrate
Lymphoplasmacytic infiltrate
Mastocytosis
Lymphohistiocytic infiltrate
These include bacterial infections including leprosy, and the sample should therefore be stained with Ziel-Neelsen, acid fast stains, Gomori methenamine silver, PAS, and Fite stains. If negative, an unspecific lymphohistocytic dermatosis may be caused by drug reactions and viral infections.Neutrophilic infiltrate
Multinucleated giant cells
- Foreign bodies indicate a foreign body granuloma.
- Specific forms of multinucleated giant cells include the Touton giant cell, which contains a ring of nuclei surrounding a central homogeneous cytoplasm, with foamy cytoplasm surrounding the nuclei. The central cytoplasm may be both amphophilic and eosinophilic.