Multiple erythematous annular lesions with peripheral collorette of scales arranged predominantly on trunk are seen in -

PITYRIASIS ROSEA:- Acute Self limiting Skin disorder of previous infectious etiology. caused by HHV 6/7Often asymptomatic. Etiology:-infectious HHV6/7Drugs causing PR like eruption-metronidazole,clonidine,gold and isotretinoin. Clinical features:-1. The primary plaque/patch- herald patch, is the first to appear and is commonly sern on the trunk, thigh and neck.2. It is well demarcated,oval/round,salmon coloured,erythematous or hyperpigmented with a fine collarette of scales.3. Secondary lesions are small plaques resembling the primary plaque distributed along the lines of the cleavage- Christmas tree pattern.4. Pruritus common. fitzpatrick textbook of dermatology , page 498