In a patient who has a pityriasis-type rash and risk factors for sexually transmitted diseases (eg, intravenous [IV] drug use, HIV infection, or promiscuity), syphilis should be considered to be present until proved otherwise. Similarly, if there is no herald patch, one should consider syphilis. Rarely, herpes zoster infection is confused with the vesicular variant of pityriasis rosea (PR). Persistent pityriasis rosea has been linked with and attributed to persistent reactivation of HHV-6 and/or HHV-7 with higher viral loads than in typical pityriasis rosea in a study of 12 patients. 
In addition to the conditions listed in the differential diagnosis, other problems to be considered include the following:
Primary HIV infection
Pityriasis amiantacea – This is a dermatitic disorder involving the scalp,  characterized by shiny asbestoslike thick scales
Cutaneous T-cell lymphoma
Subacute cutaneous lupus erythematosus
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