History: Where—what areas of skin are involved?; How long—hours, weeks, months, years? Symptoms—pruritic, painful, headache, fever, arthralgias, general malaise—did it start with 1 large patch followed by smaller patches? Quality of skin—a patch red/pink/salmon colored and enlarging, started on neck, trunk, or proximal extremities? Severity—good/bad day, spreading of lesions on trunk/proximal extremities? Mod. Factors—previous treatment? Context—associations, is it worse with exercise or bathing in hot water? Timing—when did it occur? do you remember being sick i.e. flu/sinus prior to rash?
Complete full body skin assessment. Look for “herald patch” which can predate the remainder of eruption by hours to days. Identify lesions on neck, trunk, and proximal extremities. Herald patch is skin/pink/salmon colored patch or plaque with slightly raised advancing margin. Center of patch or plaques has characteristic small fine scales of PR. The margin will have large more obvious trailing collaret of scale with free edge pointing inwards. Lesions increasing on trunk and proximal extremities. Identify thin papule and plaques. Lesions usually round to oval in shape w/ long axis following Langer’s lines of cleavage (skin folds in groin area). On posterior trunk, lesions present as “Christmas tree pattern”. Face, palms and soles often spared. Look for atypical forms of PR: inverse PR, involving the axillae and inguinal areas and sometimes the face (more common in younger children and African Americans). Usually rash starts on trunk/upper extremities and spreads downward toward feet.
None. May perform skin biopsy to confirm diagnosis. CBC/RPR (VDRL) may be indicated.
- Tinea corporis--typically not as extensive as PR and lacks “Christmas tree pattern” seen on back, scale more evident)
- Syphilis-split papules-where? Location—lips?, have systemic complaints, peripheral lymphadenopathy. Consider in persistent cases of PR since syphilis great mimicker of PR
- Drug eruptions—usually lacks scale but ask about any new medications?
- Nummular eczema—coin shaped lesions, eczematous patches on extremities often the lower legs in men and forearms and dorsa of the hands in women. 1-3 cm [larger than PR], may have vesicles and weeping but are more often lichenified and hyperkeratotic. Intense pruritus and scratch marks are often prominent.
- Guttae psoriasis—thicker scale, smaller size and lack the “fir-tree”/Christmas tree distribution
- Pityriasis lichenoides(PLEVA-acute & PLC-chronic)—Consider when lesions last >4months, recurrent crops of spontaneously regressing erythematous to purpuric papules
- PLEVA: individual lesions develop crusts, ulcers, vesicles, or pustules, which may heal with varioliform scars if dermal damage extensive; are usually asymptomatic and typically resolve within weeks. Confined to the skin except rarely when acute lesions are associated with malaise, fever, generalized lymphadenopathy, arthritis, bacteremia, or scleroderma (yes, this is correct per dermatology text vol I and II).
- PLC—(Consider when lesions last >4months) recurrent crops of spontaneously regressing erythematous to purpuric papules, papules are erythematous to red-brown and scaly; minimal-often slight scaly. Regressing over weeks to months; subside leaving hypopigmented macules that may be the presenting complaint in darker patients; can resolve spontaneously after weeks to months.