The rationale for the use of vitamin D derivatives in the treatment of psoriasis is based on the observation that patients with hypocalcemia often develop various forms of psoriasis, most notably the pustular form. In one case, a patient who had undergone thyroidectomy developed repeated flares of pustular psoriasis after decreases were made in her dosage of ergocalciferol (Vitamin D 2 ); each episode was related to severe hypocalcemia and resolved after her serum calcium levels normalized. 14 Another patient with osteoporosis experienced dramatic improvement in severe psoriasis after receiving an oral form of vitamin D. 15 This finding, along with the discovery that the bioactive form of 1,25-dihydroxycholecalciferol has been shown to inhibit keratinocyte proliferation and promote keratinocyte differentiation, 16 has led to the development of vitamin D analogs for the treatment of psoriasis.
In all cases, the therapeutic goal is to maximize treatment efficacy and the patient's quality of life, while minimizing side effects. Achieving and maintaining control of psoriatic lesions is the central goal in treatment. Physicians and patients need to understand that there is no definitive cure for psoriasis ( Figure 4 ) . Control of the disease may mean that lesions are not as thick or as red as they were before treatment, but some degree of erythema may remain. Most often, treatment does not result in complete clearing of the lesions.