Arthropod bite and analogous reaction
Early
| Wedge shape of a perivascular and interstitial infiltrate |
| Lymphocytes and eosinophils around blood vessels with eosinophils scattered interstitial in the reticular dermis |
| Slight edema of the papillary dermis |
| A discrete focus of spongiosis sometimes present in the epidermis at the site of the "bite", i.e., directly above the apex of the wedge formed by inflammatory cells whose vertex within the dermis points to the subcutaneous fat. |
Fully developed
| Infiltrate of lymphocytes and eosinophils denser and deeper than in an early lesion; the subcutaneous fat my be involved |
| Edema of the papillary dermis more marked than in an early lesion |
| Spongiosis, sometimes in company with a multiloculated vesicle and epidermal necrosis, in a focus in the center of the lesion |