Objective: Cutaneous adverse drug reactions are commonly seen in dermatology outpatient clinics thereby comprising a large part of the
pathology materials. However, the lack of information about drug usage may cause misdiagnosis. The aim of this study was to discuss criteria
that may help in recognition of drug eruptions due to histological patterns.

Methods: Ninety-two patients who were diagnosed with maculopapular rash between 2015 and 2018 at the pathology and dermatology
departments of our hospital were examined according to distribution of histopathological changes and patterns.

Results: This study was conducted to evaluate histopathological spectrum of eruption which were known to be drug related that cleared
following cessation clinically. Hyperkeratosis or parakeratosis was detected in 26.1% (24/92) and 35.9% (33/92) of all cases, respectively. The
most common feature in the epidermis was acanthosis in 88 of 92 biopsies (96%) and the least common feature was atrophy in 4 of 92
biopsies (4%). Dermal inflammation was in 89 of 92 cases (97%). Inflammation was mostly consisted of mononuclear cells. Vacuolar interface
dermatitis pattern, spongiotic dermatitis pattern, lichenoid dermatitis pattern, or leukocytoclastic vasculitis pattern was detected in 93.5%
(86/92); 58.7% (54/92); 16.3% (15/92); 7.6% (7/92) of all cases, respectively.

Conclusion: Accurate diagnoses of drug eruption are important because they may cause patients’ annoyance, hospitalization, economic load,
and sometimes be fatal. Like Ackerman emphasized drugs elicit diversity of histological changes but none of the reaction pattern are specific.