A total of 20 patients with symmetric plaque-type psoriasis were recruited for a controlled, investigator-blinded, right–left study. None of the patients had used any therapy other than emollients for 2 months prior to starting in the trial. All patients had a negative antinuclear antibody. By history, all patients had previously improved upon exposure to sunlight or ultraviolet light. Two symmetrical sites of equal severity were selected as target areas. Each patient was treated on one side with mineral oil twice daily and on the opposite side with calcipotriene 0.005% ointment twice daily. The investigator was blinded as to which site received which topical treatment. Both sides were treated with equal doses of ultraviolet B (UVB) three times weekly in graduated suberythemogenic doses. Ultraviolet B radiation was emitted by a group of 6-ft fluorescent bulbs (Light Sources FS72 T12 UVB HO) in a standard phototherapy unit.

The above regimen was continued for a total of 12 weeks. The severity of psoriasis in the target sites was rated by the examiner at baseline and at weekly intervals for the 12 weeks of study. Target sites were rated by severity of erythema, scaling, plaque elevation, and pruritus, with each of these parameters being assigned a score on a four-point scale: 0, clear; 1, mild; 2, moderate; 3, severe. The four scores were added together to arrive at a total severity score for each of the target sites.

Statistical analysis was performed using the paired t test, P values less than 0.05 were considered statistically significant.

Eleven of the 20 patients (55%) showed a greater decrease in the severity of their psoriasis with UVB plus calcipotriene compared with UVB plus mineral oil. The difference in severity scores between the two groups was statistically significant as early as week 1 (P < 0.05). The difference between the UVB and calcipotriene group versus the UVB and mineral oil group peaked between weeks 3 and 6. The differences then decreased but remained statistically significant through to week 12 (Fig. 1). There were no instances of local cutaneous irritation, but mild photosensitivity occurred symmetrically on both sides in three patients.