Acute GVHD shows vacuolar interface change of the epidermis, with intraepidermal lymphocytes and apoptotic keratinocytes.
Sometimes, the lymphocytes appear adjacent to the nechrotic keratonocytes (satellitosis).
Eosinophils are very rare in GVHD (J Cutan Pathol 2012;39:413-418).
See also Chronic GVHD.
FISH can be useful when the donor´s sex is unmatched with patient´s sex: X and Y chromosome probes can demonstrate if the lymphocytes belong to the donor or to the patient.
Lichen planus: very similar; pay attention to wedge-shaped hypergranulosis.
Erythema multiforme: very difficult to distinguish. Follicular dyskeratosis points towards GVHD.
Drug eruption: eosinophils in the infiltrate. Remember that eosinophils are very rare in GVHD (J Cutan Pathol 2012;39:413-418).
Eruption of lymphocyte recovery: although dyskeratoses are less, clinical information is crucial.
Sclerodema: nearly indistinguishable from the sclerodermatous variant of GVHD. Also, the eosinophilic sclerodermic form must be distinguished from eosinophilic fasciitis.