West A J, Berger T G, LeBoit P E
Department of Dermatology, University of California, San Francisco School of Medicine.
J Am Acad Dermatol. 1990 Oct;23(4 Pt 1):689-93. doi: 10.1016/0190-9622(90)70275-m.
This study compares the histopathologic characteristics of photodistributed and nonphotodistributed lichenoid drug eruptions in 13 patients. Both types have been said to be, in an unknown proportion, different from idiopathic lichen planus in that they can involve the deep as well as the superficial plexus, can contain eosinophils, and have parakeratotic scale. We found that these features were most often present in nonphotodistributed lichenoid drug eruptions and were seldom present in photodistributed eruptions. Thus a biopsy specimen that shows the classic features of lichen planus should not be used as evidence against a drug eruption, especially if the lesions are photodistributed.
