David Norris’s research while affiliated with University of Colorado and other places

... Erythema elevatum diutinum is a rare chronic disease, manifested by erythematous-violaceous papules, nodules, and plaques of symmetrical distribution on the extensor surfaces of the hands, feet, elbows, knees, buttocks, and lower limbs. Other presentations such as vesicular, bullous, and ulcerative morphology have also been reported [3]. Lesions can occur in atypical areas such as the trunk, retroauricular area, or palmoplantar region. ...

Reference:

Erythema elevatum diutinum in a patient with rheumatoid arthritis