| • | Short-sleeve turtle neck distribution |
| • | interval between herald patch and secondary eruption is between 2 days and 2 months |
| • | Secondary eruption typically lasts 4 to 6 weeks (but can last up to 12 weeks) |
| • | recurrence seems to be quite common |
atypical PR:
| • | PR inversa – distribution is exclusively peripheral (or intertriginous) |
| • | papular PR - generalized tiny papules instead of annuli |
| • | atypical morphology – macules may lack scaling, papules may be follicular; vesicular type = uncommon |
histology:
| • | focal parakeratosis (in mounds) |
| • | superficial perivascular infiltrate |
| • | indistinguishable from superficial gyrate erythema (erythema annulare centrifugum) |
| • | erythema dyschromicum perstans (distinct morphology) |
| • | lichen planus and lichenoid reactions (lichen pigmentosus) with PR distribution are often caused by drugs |
| • | KS/ UP (though distinct morphology) |
|
| • | pityriasis alba – longer course |
| • | nummular eczema – can cause diagnostic difficulties when localized to the trunk |
| • | seborrheic dermatitis – as a rule the scalp and face show the typical picture of seborrheic dermatitis |
|
| • | EM of the small lesion type |
| • | Gianotti-Crosti syndrome (vs. inverse PR) |
| • | secondary syphilis (check palms, soles, mucous membranes) |
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