The next reaction pattern you should look for is the Superficial and Deep Perivascular infiltrate. Sometimes it is mild and sometimes florid with associated vascular damage with fibrin deposition in a vessel lumen clinically giving a frank vasculitis with palpable purpura. Again the diseases presenting with this reaction pattern will be dermal diseases, usually covered by the red nonscaly mnemonic, CUL DVA EVIE
The annular erythemas classically give this superficial and deep perivascular infiltrate with a tight cuff of lymphocytes around the vessels of the superficial and deep dermal plexus. This reaction pattern is in it's purest form in the annular erythemas(EAC, Erythema chronicum migrans, Erythema gyratum repens etc)but it is seen in a more non specific way in other reaction patterns involving lymphocytes and other inflammatory cells which initially have to make their way out of the blood vessels into the tissues! So do not call this the main reaction pattern unless it is all you have!
This reaction pattern is also seen in lupus erythematosus and dermatomyositis but you need a bit of Interphase damage as well to call either of those two diagnoses. Some measles like viral exanthems show it and some mild drug reactions where the addition of a few eosinophils to the perivascular lymphocytes help to point you in that direction.
A superficial and deep perivascular reaction pattern plus extravasated red cells is typically seen with the pigmented purpuric dermatoses found around the ankles.
A true vasculitis is characterized by neutrophils or lymphocytes infiltrating a vessel wall, plus pinkish fibrin being laid down in the wall or having nuclear dust from fragmented neutrophils within and around a vessel plus some extravasated red blood cells. These vasculitides can be classified histologically as leukocytoclastic when neutrophils are the predominant cell seen and lymphocytic when lymphocytes are predominant but the later a lesion is biopsied the more likely you are to see lymphocytes rather than neutrophils! Remember true vasculitis gives rise to palpable purpura clinically.
Large vessel vasculitis is seen deep in the reticular dermis with fibrin deposition in the thickened swollen walls. When one of these vessels is involved you get frank necrosis of the skin eg in Polyarteritis nodosa (See part 4 of Module) or Temporal arteritis or in some cases of Wegener's granulomatous vasculitis.
