Histopathologic Pattern Analysis

• Dermatitis is not particularly useful without qualification, since the skin becomes inflamed in response to a myriad of causes.
• Pattern-analysis, at low magnification, relates inflammatory patterns to various types of skin diseases.
• Details at higher magnification often allow for a specific diagnosis.
• Perivascular (interstitial) dermatitis

  Inflammatory reaction centred on the superficial and/or deep dermal vessels
• Types of perivascular (interstitial) dermatitis

  • Pure perivascular (interstitial) dermatitis
  • Spongiotic perivascular (interstitial) dermatitis
  • Hyperplastic perivascular (interstitial) dermatitis
• Pure perivascular (interstitial) dermatitis

  • Acute edema in superficial dermis, perivascular accumulation of inflammatory cells
• Spongiotic perivascular (interstitial) dermatitis

  • Hypersensitivity caused by yeast, tick, lice, fleas
• Hyperplastic perivascular (interstitial) dermatitis


  • Chronic hypersensitivities, altered keratinization, lick dermatitis
• Interface dermatitis

  Immune-mediated &/or autoimmune, drug reactions, viral infections
• Interface dermatitis

  • Hydropic degeneration, lichenoid band of inflammatory cells
• Vasculitis

  Inflammation and damage of the blood vessel wall
• Nodular and diffuse dermatitis

  Traumatic implantation of foreign material / bacteria / fungi / protozoa
• Nodular or multinodular dermatitis

  • Discrete cluster(s) of inflammatory cells within the dermis
• Diffuse dermatitis

  • Dense diffuse inflammatory cell infiltrate with effacement of the normal dermal architecture
• Vesicular & pustular dermatitis

  Intraepidermal vesicles / pustules due to acantholysis, coalescing ballooning degeneration in viral dermatitis, intense intra- &/or intercellular edema of the epidermis
• Vesicular & pustular dermatitis

  • Subepidermal vesicles / pustules due to dermoepidermal separation, severe subepidermal edema and/or cellular infiltration
• Perifolliculitis, folliculitis, furunculosis

  Especially due to bacteria (Staph) or fungi (ringworm) or parasites (demodex)
• Perifolliculitis

  • Accumulation of inflammatory cells surrounding hair follicle
• Folliculitis


  • Accumulation of inflammatory cells within the wall &/ or the lumen of the hair follicle
• Furunculosis

  • Effacement / rupture of the hair follicle due to intense inflammation
• Panniculitis


  Often extension from nodular or diffuse dermitis; nutritional, injection, idiopathic
• Panniculitis

  • Lobular, septal or diffuse inflammation
• Atrophic dermatosis

  Usually due to endocrine disorders; less nutritional or developmental dermatoses
• Atrophic dermatosis

  • Orthokeratotic hyperkeratosis, epidermal melanosis, sebaceous gland atrophy and follicular changes indicative of hair cycle arrest