Re: Erythema multiforme (EM)

[Anonymous]

DIFFERENTIAL DIAGNOSIS
ERYTHEMA MULTIFORME
Interface vacuolar change with numerous necrotic keratinocytes

Diagnostic Pearls

* Erythematous targetoid lesions
* Lichenoid interface dermatitis with vacuolar change and intraepidermal necrotic keratinocytes.
* Subepidermal vesiculation with papillary dermal edema progressing to bullae formation.

LICHEN PLANUS
Hyperkeratosis, hypergranulosis, irregular acanthosis

Diagnostic Pearls

* Polygonal, planar, pruritic, purplish papules, present in 4th to 6th decade, more commen in women
* Compact ortho and hyperkeratosis, wedge-shaped hypergranulosis centered around acrosyringium
* Band-like infiltrate of lymphocytes (rare, if any plasma cells); necrotic keratinocytes (civatte bodies) are limited to lower epidermis

LUPUS ERYTHEMATOSIS
Discoid lupus erythemtous: Epidermal thinning, hyperkeratosis, superficial and deep dermal perivascular and peri adnexal infiltrate involving subcutaneous tissue.

Diagnostic Pearls

* Erythematous, annular scaly plaques on face, upper chest and extremities
* Superficial and deep dermal perivascular and periadnexal infiltrate may involve subcutaneous tissue
* Dermal mucin deposition