can trigger an immune response against the keratinocyte ; causing epidermal necrosis and the appearance of the classic targetoid skin lesions . previously reported nail changes are edema of the nail folds and nail plate detachment . in some cases of em , these changes can cause permanent nail deformity , therefore early diagnosis is crucial in order to prevent permanent sequelae . a 26-year - old man visited the dermatology clinic at the national institute of medical sciences  salvador zubirn  with several skin lesions in upper extremities , palms and soles . physical examination revealed widespread red and targetoid macules with dusky centers , with adjacent irregular erithematous areas in the nail bed . he referred oral ulcers , fever , chills and the use of a nonsteroidal anti - inflammatory drug ( nsaid ) 3 days before the onset of the lesions . based on the clinical findings and the presence of oral ulcers before the onset of the skin lesions , the diagnosis of em secondary to herpes simplex virus infection was made . represents up to 90% of cases , and the most common agent is herpes simplex virus ( hsv ) . drugs like nsaids , sulfonamides , antiepileptics and antibiotics have also been implicated in the development of this disease . less frequently it is associated to autoimmune disorders , malignancy , immunizations , radiation , and menstruation . the clinical findings are characterized by acrally distributed , targetoid lesions with concentric color variation that sometimes can be accompanied by mucosal erosions . hla dqb1 * 0301 , a33 , b35 , b62 , dq3 and dr53 have been related to this disease , therefore genetic susceptibility can be a predisposing factor . cell - mediated immune reaction against viral antigen - positive cells and several inflammatory mediators have been implicated in the pathogenesis of his disease . after several days these lesions develop concentric alterations in color resulting in targetoid lesions . appearing in the distal parts of the extremities and the most important differential diagnosis are reaction to arthropod bites , behet disease , fixed drug eruption and acute febrile neutrophilic dermatosis . edema of the nail folds and nail plate detachment with subsequent nail deformity are some of the nail findings that have been reported . in our case , these erythematous areas are adjacent to the skin lesions of em , so this nail change may be explained by the inflammatory process that cause vessel dilatation with an alteration of the blood supply in the nail bed . the patient was treated with topical corticosteroids twice at day with resolution of his lesions in 10 days without sequelae . in conclusion , it is important to report the variability of the nail changes in these conditions with the aim of early diagnosis , treatment and sequelae prevention . the nail changes en erythema multiforme are underestimatederythronychia is a new nail finding in this disease that had been not previously reported . the nail changes en erythema multiforme are underestimated erythronychia is a new nail finding in this disease that had been not previously reported .
erythema multiforme is an acute muco - cutaneous hypersensitivity reaction with a variety of etiologies . 
 it is characterized by a skin eruption , with or without oral or other mucous membrane lesions . 
 general characteristics and treatmet have been described , but nail findings are rarely reported here we present a 26-year - old patient with acral erythema multiforme and erythronychia adjacent to skin lesions on the back of the hands . to our knowledge 
 this association had not been reported before .