Skin histopathology can be divided into 7 patterns. The red scaly diseases PMs PET (AL) clinically correspond with the 2 epidermal histological patterns, namely Psoriatic or Spongiotic.
The red nonscaly diseases CUL DVA EVIE have essentially dermal histological patterns and they are Superficial and deep perivascular, Granulomatous, Interface, Lichenoid and Vesiculobullous. The Interface pattern may show epidermal features as it occurs at the level of the basement membrane eg Discoid lupus and the Vesiculobullous pattern may also show epidermal features if the vesicles or bullae are in the epidermis which is the case in herpes virus and bullous impetigo.
An 8th deep reaction pattern is Panniculitis when inflammation is in the fat layer in either the septae between the fat lobules or in the lobules themselves.
To diagnose an inflammatory skin disease you look at the Epidermis and then the Dermis and see which reaction pattern predominates. You may have more than one reaction pattern. When you have decided, consider the diagnostic possibilities and look for features which justify your choice. Alternatively look for other features on the slide before making a definite diagnosis and avoid biasing yourself!
