Snapshot A 12-year-old girl was recently treated for walking pneumonia and was found to be positive for mycoplasma. A few days into her illness, she developed multiple raised lesions over her palms, back of hands, and extensor forearms. These lesions were targetoid and mildly itchy. There were no lesions on her mucous membranes. Introduction Hypersensitivity reaction of the skin Inflammation and cell death secondary to macrophage and CD8 T lymphocyte influx Common, acute, mucocutaneous disease with classic target-shaped lesions in a symmetric distribution Causes most common = infection Herpes simplex Mycoplasma pneumonia upper respiratory infections less common = drugs e.g., sulfonamides, β-lactams, phenytoin idiopathic Often affects young adults (18 - 30 years old especially) Distinct from SJS/TEN, which is amore severe mucocutaneous reaction that is usually caused by a medication Presentation Skin exam raised (papular), target lesions with multiple rings and dusky center (in contrast to annular lesions, as in urticaria) three concentric zones of color from center to outer ring central dusky/dark area that can be crust or vesicle paler pink or edematous zone peripheral red/dark ring negative Nikolsky sign (as opposed to SJS/TEN) most commonly involves palms/soles backs of hands and feet extensor aspects of forearms and legs May involve mucous membranes May have systemic signs Evaluation Based on symptoms and clinical history recent history of infection can aid diagnosis Differential Diagnosis SJS/TEN (flat lesions, tender, always with mucous involvement, + Nikolsky sign) Urticaria (annular lesions) Erythema nodosum Viral exanthems Treatment Supportive care Corticosteroids if severe Treat underlying cause if identified oral acyclovir for HSV Prognosis, Prevention, and Complications Prognosis typically self-limited Prevention treat chronic herpes infections Complications usually none