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Background: Acute generalized exanthematous pustulosis (AGEP) is a potentially severe adverse cutaneous drug reaction, which typically occurs within 24–48 h after the intake of the culprit drug. Summary: AGEP is characterized by numerous sterile subcorneal pustules on erythematous skin and in less than a third of cases it can be associated with organ manifestations possibly leading to life-threatening symptoms (e.g., cholestasis, nephritis, and lung and bone marrow involvement). In contrast to generalized pustular psoriasis, it can involve mucosal regions and typically resolves rapidly if the culprit drug is removed, and adequate therapy with topical or systemic steroids administered. Diagnosis based on patient history, clinical signs, and characteristic cutaneous histology is rarely challenging. Identification of the culprit drug may be aided by patch testing or lymphocyte transformation tests that are of limited value. Key Messages: Recent experimental data reviewed herein are supportive of an early role of drug-induced innate immune activation and innate cytokines such as interleukin (IL)-1, IL-36, and IL-17 in the pathogenesis of AGEP. This explains the rapid onset and neutrophilic character of the cutaneous inflammation, but also provides new avenues for in vitro tests aimed at better identifying the culprit drug. [ABSTRACT FROM AUTHOR]

Cutaneous lichenoid drug eruptions (LDE) are adverse drug reactions (ADR) characterized by symmetric, erythematous, violaceous papules reminiscent but rarely fully characteristic of lichen planus (LP). We aimed to analyse the literature describing cases of LDE within the last 20 years to provide additional insight into culprit drugs, typical latency to onset of the eruption, the spectrum of clinical presentations, severity and management. A literature search was conducted in MEDLINE between January 2000 and 27 January 2021. The keywords 'lichenoid drug rash' and 'lichenoid drug eruption' were used. Cases were included if LDE diagnosis was made, and culprit drugs were identified. A total of 323 cases with LDE were identified from 163 published case reports and studies. The mean patient age was 58.5 years (1 month to 92 years), and 135 patients (41.8%) were female. Checkpoint inhibitors (CKI) were the most frequently reported culprit drugs (136 cases; 42.1%), followed by tyrosine kinase inhibitors (TKI) (39 cases; 12.0%) and anti‐TNF‐α‐monoclonal antibodies (13 cases; 4.0%). The latency between initiation of the drug and manifestation was 15.7 weeks (range: 0.1–208 weeks). After discontinuing the culprit drug, the median time to resolution was 14.2 weeks (range: 0.71–416 weeks). One hundred thirty‐six patients (42.1%) were treated with topical, and 54 patients (16.7%) with systemic glucocorticoids. Overall, we conclude that, albeit rare, LDE is challenging to diagnose ADR induced by mostly CKI, TKI, and biologics. Treatment modalities resemble that of lichen planus, and the culprit drugs had to be discontinued in only 26%, which is low compared with other types of adverse drug reactions. This is probably due to the low risk of aggravation (e.g. toxic epidermal necrolysis) if the drug is continued and the benefit/risk ratio favouring the drug, as is often the case in cancer therapy. [ABSTRACT FROM AUTHOR]