3.2 Drug induced maculopapular exanthema
In general, about 7% of hospitalized patients develop drug hypersensitivity reactions of variable severity, and exanthema occurs in 2-3% of these cases (70, 71 ).
Both, drugs and metabolites of drugs might elicit exanthematous drug-hypersensitivity reactions (Table 4).
Some skin lesions observed in COVID-19 patients might result from cutaneous type IV (T-cell mediated) drug hypersensitivity reactions. Typical immunologic characteristics of maculopapular eruptions are summarized in Figure 5B (type IVb) and 5C (type IVc) and histologic features are summarized in Table 5 and shown in Figure 6B. The most common histologic feature of drug-induced maculopapular exanthema is a perivascular dermal lymphohistiocytic infiltrate with or without infiltration of eosinophilic granulocytes. The epidermis can be normal or exhibit interface changes with vacuolar degeneration of the basal layer, apoptotic keratinocytes and exocytosis of lymphocytes can be present. Additional features can be edema in the upper dermis, extravasation of red blood cells and dilatation of blood vessels. It is often impossible to histologically distinguish viral and drug induced exanthema. Lichenoid – and less frequently- spongiotic or psoriasiform pattern of reactions may be related to maculopapular drug reactions. Sometimes even systemic eosinophilia and elevated CRP levels might occur (72 ). Typical immunologic characteristics of maculopapular eruptions are summarized in Figure 5B (type IVb) and 5C (type IVc) and histologic features are summarized in Table 5 and shown on Figure 6B.