Fas‐ligand staining in non‐drug‐ and drug‐induced maculopapular rashes

Background: Morphologically and histopathologically, drug‐ and non‐drug‐induced maculopapular rashes can be almost indistinguishable. It has been postulated that Fas‐ligand (Fas‐L) is involved in the pathogenesis of drug rashes but not in the genesis of rashes, such as viral exanthems, that are not induced by medications. Aim: This study sought to determine if epidermal Fas‐L is a distinguishing feature in the pathology of drug and non‐drug maculopapular rashes. Methods: Archived skin biopsies of patients with a confirmed diagnosis of drug or non‐drug maculopapular rashes (n = 10 each) and positive and negative controls were retrieved for immunohistochemical staining for Fas‐L. The proportion of Fas‐L‐positive skin biopsies were compared. The presence of tissue eosinophilia was also evaluated. Results: Ten percent of non‐drug‐induced rashes were Fas‐L positive compared to 50% of drug rashes (p = 0.05). Twenty percent of non‐drug exanthems had moderate tissue eosinophilia, while 60% from drug rashes had moderate to dense tissue eosinophilia (p = 0.17). Conclusion: There is a trend toward Fas‐L being more prevalent in the epidermis of drug maculopapular rashes, although this did not reach statistical significance. This is possibly because of the small sample size. Wang ECE, Lee JSS, Tan AWH, Tang MBY. Fas‐ligand staining in non‐drug‐ and drug‐induced maculopapular rashes.