Have you ever considered doing an internal cleanse? I have psoriasis also and it goes away after I do a 60 to 90 day cleanse. When it starts to reappear I cleanse again. I'm a firm believer that our diet and the build up of toxins in our body are major contributors to health issues.
There are many modalities of treatments available including, steroids and other local applications, PUVA and other phototherapies.
'Ointment and creams containing coal tar, dithranol (anthralin), corticosteroids like Topicort Desoximetasone), vitamin D3 analogues (for example, calcipotriol), and retinoids are routinely used.'
There are other measures to be taken and your doctor can tell you more about it.