Condition	Key clinical features	Tests
Lichen nitidus	1- to 3-mm, skin-colored, raised, flat-topped papules on trunk, flexor surfaces of extremities, dorsal hands, or genitalia	Skin biopsy is diagnostic and often done
Pityriasis lichenoides	2- to 10-mm, round or oval, red-brown papules progressing to hemorrhagic lesions on trunk, thighs, or upper arms	Skin biopsy is diagnostic and routinely done
Pityriasis rubra pilaris	Red or orange follicular papules on fingers, elbows, knees, trunk, or scalp; often mistaken for psoriasis; characterized by “skip areas” of normal skin	Skin biopsy is occasionally nonspecific but can help exclude other conditions, and is routinely done
Rickettsialpox	Initial lesion, which may not be noticed by patient, begins as papule and evolves to vesicle, then crusts; generalized maculopapular vesicular exanthem can involve palms and soles; most common in large cities40	Serology (immunoglobulin G for Rickettsia rickettsii and Rickettsia akari); biopsy with direct fluorescent antibody testing may be diagnostic but is not often done*
Rubella†	Round, pink macules and papules starting on forehead, neck, and face, then spreading to trunk and extremities, including palms and soles	Serology; skin biopsy is nonspecific and not often done*
Rubeola	Maculopapular purple-red lesions that may become confluent; start on face and behind ears and at anterior hairline; Koplik spots (i.e., tiny red or white spots with red halo on buccal mucosa)	Serology; skin biopsy is usually nonspecific and not often done*