Dermatopathology

  • Diagnosis unclear
  • Poor response to treatment
  • Evolution from one condition to another
  • Symptoms with no clinically identifiable disease

  • Unaltered primary lesion usually from the center of the lesion. Newly developed mature lesions are commonly chosen.

  • Exceptions: early lesions in cutaneous small vessel vasculitis or immunobullous diseases. Some lesions require biopsy of both affected and unaffected skin (ulcers, bullae, lesions with subtle changes compared to unaffected skin)
  • Preferred site:
    • Urticaria: edge of lesion + unaffected skin
    • Vasculitides: center of early lesion
    • Livedo reticularis: center of pale area
    • Autoimmune blistering disorder: early vesicle or entire bullae
    • Alopecia: active advancing edge
    • Infectious diseases: mature lesions
    • Ulcerative dermatoses: active edge or early lesion
    • Pigmentary lesions: include edge of lesion + unaffected skin

  • Superficial shave: epidermal pathologies or for exophytic benign lesions

  • Deep shave/saucerization: Deeper shave that removes more of the upper to mid-dermis
  • Curettage: for superficial lesions limited to the epidermis
  • Punch: for pathology lying within the dermis and a small sampling is likely to be sufficient to represent the disease process
  • Incisional: removal of part of the lesion
  • Excisional: removal of the entire visible lesion with a scalpel

  • Careful handling is necessary to avoid artifacts

  • Routine histologic analysis: specimen fixed in 10% neutral buffered formalin solution
  • Microorganism tissue culture: specimen in a sterile container with non-bacteriostatic saline
  • Direct immunofluorescence: specimen must be flash-frozen, put in normal saline < 24-48 hours or placed in specialized transport medium (Michel’s solution)
  • Electron microscopy: specimen fixed in paraformaldehyde and glutaraldehyde in a cacodylate buffer

Perivascular dermatitis:

  • Inflammatory infiltrate around dermal blood vessels

Interface dermatitis:

  • Inflammation or degenerative changes at the junction of the dermis-epidermis
  • May be subdivided into vacuolar and lichenoid

Spongiotic dermatitis:

  • Spongiosis (intercellular edema) leads to widened spaces between keratinocytes and elongation of intercellular bridges
  • Varies from microscopic foci to grossly visible vesicles/intraepidermal bullae
  • Exocytosis of inflammatory cells from blood vessels into the epidermis is often associated

Psoriasiform dermatitis:

  • Regular pattern of epidermal hyperplasia (elongation of rete ridges)
  • Not exclusive to psoriasis
  • Thickened papules and plaques with scales

Vesiculobullous and pustular dermatoses:

  • Intraepidermal vesicles or bullae can form due to disease mechanisms such as spongiosis, acantholysis (loss of intercellular connections between keratinocytes due to disruption of desmosomes) and subepidermal edema
  • Pustules form due to intraepidermal accumulation of neutrophils
  • Subepidermal vesiculation occurs at the junction between the epidermis and dermis or between the mucosa and submucosa. May be due to autoantibodies, inflammation, toxic or metabolic insults.

Vasculitis:

  • Inflammatory damage of blood vessels leading to deposition of fibrin and thrombus formation
  • Most common: leukocytoclastic vasculitis

Nodular and diffuse:

  • Resembles perivascular dermatitis, but the inflammatory infiltrate is enlarged and is coalesced forming nodules within the dermis
  • Nodules can fill entire dermis creating a diffuse pattern
  • May be subdivided based on the main inflammatory cell found

Folliculitis:

  • Inflammatory cells present in the wall and lumen of a hair follicle
  • Due to infections, drugs, occlusion, unknown etiology

Fibrosing/sclerosing:

  • Altered production of collagen
  • Often due to injury or autoimmune connective tissue disease
  • Pattern characterized by: abnormal fibrous dermal tissue with increased fibroblasts and increased collagen (fibrosis) OR homogenized, enlarged and eosinophilic collagen with few admixed fibroblasts (sclerosis)

Panniculitis:

  • Inflammation of the subcutis
  • Difficult to diagnose due to nonspecific clinical presentation and varying histopathologic changes
  • Most common: erythema nodosum

Invisible dermatoses:

  • Dermatosis without an immediately recognizable pattern
  • Examples:
    • Vitiligo
    • Ichthyosis
    • Tinea versicolor
    • Urticaria

Hematoxylin and eosin (H&E):

  • Standard stain in dermatopathology
  • Hematoxylin marks basophilic structures in blue-purple
  • Eosin marks eosinophilic structures in pink-red

Verhoef-van Gieson:

  • Elastic tissue

Brown-Brenn

  • Modified tissue gram stain for bacteria

Periodix acid Schiff or Grocott methenamine silver stain:

  • Fungus

Ziehl-Neelsen or Fite stain

  • Mycobacteria

  • Amyloid: Congo red, serius red, pagoda, crystal violet, methyl violet, thioflavin T (yellow-green by fluorescence)
  • Mucin: alcian blue, colloidal iron, crystal violet
  • Acid mucopolysaccharides: alcian blue, colloidal iron, crystal violet
  • Elastic tissue, collagen, muscles, and nerves: Orcein, verhoeff-van Gleson or Welgert

  • Immunohistochemistry utilizes immunologic techniques to identify cellular antigens through antibody binding that are not clearly seen on H&E-stained sections

  • Commonly used stains for:
    • Epithelial tumors: adipophilin, Bcl2, Ber-EP4, CEA, CK5/6
    • Melanocytic and neural tumors: S100, Melan-A (Mart-1), MITF, tyrosinase, SOX10, BRAF V600E, P75, PNL2, pHH3
    • Neuroendocrine tumors: chromogranin, CK20 (most sensitive for Merkel cell carcinoma especially combined with negative TTF1 staining), neurofilament, synaptophysin, TTF-1
    • Mesenchymal tumors: caldesmon, calponin, CD99, desmin, factor XIIa, smooth muscle actin, vimentin
    • Vascular tumors: CD31, CD34, podoplanin (D2-40), c-MYC, ERG, HHV-8
    • Histiocytic tumors: CD1a, CD68, CD163, CD207 (langerin), S100
    • Mast cell tumors: CD117, mast cell tryptase
    • Cutaneous metastases: CK7, CK20, PSA
    • Cutaneous lymphoproliferative disorders: AKL, Bcl-2, Bcl-6, kappa and lambda immunoglobulin light chains, CD3, CD4, CD5, CD8