Biopsy petechiae right arm: spongiotic psoriasiform dermatitis w/purpura. Drug eruption in a pt. W/underlying psoriasis or eruptive psoriasis exacerbated by a drug. What does this mean? Drug allergy?

See your doctor. This is what is called a "descriptive" path report. In these cases we construct a list of conditions that can produce this type of reaction pattern then try to narrow it down if possible. In these cases a good solid history needs to be taken to identify any possible cause (drug or other). I am afraid this can be a challenging process and sometimes we do not find the actual diagnosis. Good luck.
Psoriasis Flare. There are a number of medications that can exacerbate psoriasis: lithium, beta blockers, corticosteroids, antimalarials, alcohol, nsaids, ace inhibitors, gold salts and interferon.