Fig. 6.1
Moderately compact orthohyperkeratosis, hypergranulosis, mild acanthosis, saw-toothing of the tips of the rete, few dyskeratotic basal cells, and a band-like lymphocytic infiltrate are characteristic of lichen planus
What Is Lichenoid Dermatitis?
In classifying the various inflammatory disorders of the skin by their patterns, interface dermatitis refers to the disorders in which the primary site of pathology is the interface between the epidermis and the dermis; that is, the dermo–epidermal junction. Interface dermatitis is then divided into two subgroups: vacuolar and lichenoid.
The prototype of vacuolar interface dermatitis is erythema multiforme, and the features are:
Basal vacuolization (also known as hydropic degeneration or vacuolar degeneration of basal cells)
Variable dyskeratosis
Superficial lymphocytic infiltrate
The prototype of lichenoid interface dermatitis is lichen planus (LP) and the histological features are:
A band-like, usually dense lymphocytic infiltrate in the papillary dermis that obscures the dermo–epidermal junction
Squamatization of basal cells, that is, basal cells lose their identifiable features and instead become larger with evidence of squamous differentiation (more deeply eosinophilic cytoplasm like differentiated keratinocytes), a phenomenon that has been referred to also as premature keratinization/cornification, and manifests histologically as dyskeratosis
Epidermal hyperplasia with characteristic saw-tooth appearance to the rete, hypergranulosis, and compact orthokeratosis
Lichenoid dermatitis or lichenoid interface dermatitis, is a histological term used for referring to a combination of histological findings close to those of LP . Disorders in this category include those with a superficial infiltrate and disorders in which the infiltrate may extend to the deep plexus. The former include
lichenoid drug eruption (which is often photoinduced)
lichen nitidus
lichenoid keratosis
lichenoid capillaritis (lichen aureus)
lichenoid mycosis fungoides MF
pityriasis lichenoides chronica PLC, and
keratosis lichenoides chronica KLC.
The latter include lichenoid lupus erythematosus and lichen striatus.
So Is Lichenoid Dermatitis a Legitimate Diagnosis to Provide on a Pathology Report?
Not if there is no histological differential diagnosis and degree of likelihood of each diagnosis. Most of the above disorders have characteristic histological findings that, with some clinical information, a diagnosis should be made in most cases. The findings in lichen nitidus, lichenoid keratosis, lichen aureus, lichenoid MF, and lichen striatus are so characteristic that reporting their findings here is unnecessary.
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