Except for the cases that present with the classic herald patch and the subsequent christmas tree pattern, the rash of pityriasis rosea can also look like eczema, ringworm or psoriasis. Infection with syphilis also can cause a similar rash.
I would go with --> VDRL which is the proper screening test for Treponema pallidum.
However, beware that even if VDRL is + you should do FTA-ABS which is the most specific test for Treponema pallidum.
P.rosea is a papulosquamous eruption consisting of multiple oval shaped scallling lesions which are truncal in distribution. this eruption resembles the papulosquamous eruption of secondary syphilis (although the rash here often involves palms & soles). the etiology of p.rosea is unknown, but it is FELT to be viral. it is a self limiting illness lasting several weeks to a few months, and there is no adequate treatment other than symptomatic treatment of pruritus, when necessary.