Pityriasis rosea usually involves the following: it begins generally with something called a 'herald' patch (kind of announcing what is to come, if you will), a round/oval pink patch 3-6 cm in diameter. This is followed 1-2 weeks later with pinkish oval lesions, up to 100 or so in number, about 4-5mm in diameter. These lesions often have a ring of scale around their border, and can form a "christmas tree" pattern on the trunk, with the base of the tree on the waist. This usually resolves spontaneously, on its own within 1-2 months. The exact cause of this is unknown (some think that its related to a virus, others to exposure to certain medications). 1 of 4 patients (25%) can experience fever, headache, sore throat, fatigue, but back pain is not related to the disease.
In general, pityriasis is not treated, as it resolves on its own. Your back pain, then, if it is new, is not likely related to your skin condition. I would recommend having your back looked at by a physician, either your primary care physician or by the emergency room, if necessary. Back pain can be related to many things, including injury, kidney stones/infection, and others. You should have it evaluated, however, and by a professional, and soon.
I hope that I have been of some help, and I hope that you feel better. I've had back pain before, and I know how unpleasant it can be. Take care
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