Working your way down from the epidermis the next reaction pattern you will meet will be what is called an Interphase pattern. This means the action is centred on the dermoepidermal junction and involves the basal cells including melanocytes and has some inflammatory cells , usually lymphocytes and histiocytic (scavenger) cells abutting the basement membrane and also passing through into the basal layers of the epidermis. The basement membrane may well be damaged and keratinocytes may shrivel up and become eosinophilic apoptotic cells. Because of damage to these basal layers the epidermis will look thinner. It is also useful to see if this process involves the walls of the hair follicles because if it does it suggests lupus erythematosus.
The diagnoses that mainly show this Interphase pattern are in the red nonscaly ballpark CUL DVA EVIE namely Lupus erythematosus, Drug reactions, some Viral exanthems and Erythema multiforme.
Lichenoid pattern we will deal with in the next section but it is characterised by a wide band of lymphocytes and histiocytic cells in the upper dermis, much wider than you see with an Interphase picture, although it also can show basal layrer damage. As the name suggests this pattern is mainly seen with lichen planus and its variant forms.
