Condition	Description	Clinical presentation	Diagnosis and management
Tinea corporis	Scaly, erythematous annular plaques with raised borders that spread centrifugally	Lesions develop after close contact with infected persons, animals, or soil; warm, moist environments exacerbate lesions	Potassium hydroxide preparation may detect segmented hyphae
			Treatment options include topical and systemic antifungals
Erythema migrans (Lyme disease)	Expanding, erythematous, annular rash with or without central clearing	Lesion appears three to 30 days after tick bite, often preceded by an influenza-like prodrome of fever, malaise, and myalgias	Diagnosis is clinical
			Treatment options include doxycycline, amoxicillin, cefuroxime (Ceftin), and ceftriaxone (Rocephin)
Plaque psoriasis	Well-demarcated, erythematous, annular plaques with adherent silvery scales	Pruritic lesions often associated with stress, alcohol, or friction	Diagnosis is clinical
			Treatment options include topical steroids and vitamin D analogues for mild cases; and systemic corticosteroids, phototherapy, and biologic agents for severe cases
Erythema multiforme	Multiple raised, annular, target-like lesions with central erythema	Lesions develop over a few days and usually resolve within three to five weeks without treatment; 90% of cases are associated with herpes simplex virus type 1, and 10% of cases are associated with medications or vaccinations	Diagnosis is clinical
			Treatment options include antivirals and systemic corticosteroids for recurrent symptoms
Lichen planus	Violaceous, flat-topped papules with fine white or gray reticular, lacy lines on top of the rash	Pruritic rash that bleeds with trauma; most commonly involves the ankles and volar surfaces of the wrist; lesions can be intraoral; associated with certain drugs and hepatitis C infection	Diagnosis is clinical, but biopsy can confirm
			Treatment options include topical corticosteroids, systemic glucocorticoids, and ultraviolet A or B phototherapy
Nummular eczema	Coin-shaped, erythematous, scaly, annular lesions	Intensely pruritic; most commonly involves the extremities	Diagnosis is clinical; potassium hydroxide preparation can rule out tinea corporis
			Treatment includes minimizing skin dryness and reducing exposure to skin irritants; topical corticosteroids for mild symptoms; and ultraviolet B phototherapy and systemic corticosteroids for severe symptoms
Pityriasis rosea	Salmon-colored, demarcated, annular or ovoid lesions with scaly borders slanted backward	Usually asymptomatic; more common in females; follows skin cleavage lines	Diagnosis is clinical
			Treatment options include topical corticosteroids, oral antihistamines, and ultraviolet A or B phototherapy; systemic corticosteroids may be used for severe symptoms
Urticaria	Pruritic, red, edematous plaques	Intensely pruritic; may affect any area of the body; usually lasts 90 minutes to 24 hours	Diagnosis is clinical
			Empiric treatment options include antihistamines and corticosteroids