Introduction

UVB, either alone or in combination with topical agents, has been used to treat psoriasis for many decades (Anderson et al., 1984). Typically, fluorescent lamps were used with a broad spectral emission including some wavelengths <290 nm, within the UVC waveband (for example: FS20, Westinghouse, Pittsburgh PA; TL-12, Philips, Eindhoven, the Netherlands). Pioneering work by Parrish and Jaenicke (1981) on the action spectrum for clearance of psoriasis showed that wavelengths <290 nm, although erythemogenic, were therapeutically ineffective. Subsequently, a novel fluorescent lamp was developed with a narrow emission peak around 311 nm (TL-01, Philips) and only 0.1% of its output <290 nm (Figure 1) (Ibbotson et al., 2004). Several small-scale clinical studies have shown an improved response of psoriasis to this narrowband lamp compared with conventional broadband phototherapy (van Weelden et al., 1988; Storbeck et al., 1993; Coven et al., 1997; Walters et al., 1999). Narrowband UVB phototherapy is now used widely in the UK, continental Europe, and increasingly in the USA (Zanolli, 2003; Ibbotson et al., 2004).

Figure 1.

Emission spectra of the two lamps. The emission spectra of the selective broadband lamp (UV6) (solid line) and narrowband lamp (TL-01) dashed line.

Full figure and legend (10K)

Some concern has been raised about the potential carcinogenic risk of narrowband UVB. Young (1995) summarized data from murine studies (van Weelden et al., 1988; Flindt-Hansen et al., 1991; Wulf et al., 1994; Gibbs et al., 1995) as indicating that narrowband UVB may be two to three times more carcinogenic per minimal erythema dose (MED) than conventional broadband UVB. It was suggested (Young, 1995) that any increased cancer risk would be negated by the increased efficacy of narrowband UVB. However, although clinical trials have shown that narrowband UVB is more effective than broadband UVB, the actual differences in response to treatment are relatively small. Therefore, the relative risk of narrowband UVB phototherapy compared to broadband remains uncertain, particularly as follow-up studies of patients are still of short duration (Weischer et al., 2004; Man et al., 2005).

As well as the archetypal conventional broadband UVB sources (FS20, TL-12), fluorescent lamps with relatively little emission <290 nm are also available. That these so-called "selective" broadband sources would be effective to treat psoriasis was predicted by Parrish and Jaenicke (1981). We are not aware of any murine studies comparing directly the non-melanoma cancer risk of selective broadband lamps with either conventional broadband UVB or narrowband UVB lamps. In the absence of such information, another method of predicting skin cancer risk for a particular lamp is to use the photocarcinogenesis action spectrum published as an international Standard by the Commission Internationale de l'Eclairage (CIE). The recent standard (CIE, 2006) is derived from experimental animal data and is modified to estimate the non-melanoma tumor response in human skin. By combining the spectral power distribution of a specific lamp with the action spectra for both erythema (CIE, 1998) and photocarcinogenesis (CIE, 2006), it is possible to calculate the carcinogenic risk per unit erythemal dose. The results of these calculations indicate that narrowband UVB lamps will be 1.5 times more carcinogenic than selective broadband UVB lamps. Whether selective broadband UVB phototherapy is likely to be a safer option than narrowband UVB clearly depends on the relative efficacy of the two lamp types in treating psoriasis. We are not aware of any studies comparing selective broadband and narrowband UVB where clearance of psoriasis has been used as an end point. We have therefore performed a randomized, observer-blinded comparison of these light sources in 100 patients with psoriasis.

Results

Participant flow

Patients were recruited between May 2003 and November 2004, with the follow-up assessments completed by June 2005. Baseline characteristics of the two treatment groups are shown in Table 1 and the trial profile is shown in Figure 2. Of the 192 sequential patients screened for inclusion, 68 were excluded under the protocol exclusion criteria, 18 refused to take part in the trial, and in six patients a medical decision was made by the phototherapy clinician to assign the patient to one or other treatment. Thus, 100 patients were randomized, 50 being assigned to TL-01, and 50 to UV6.

Figure 2.

The trial profile.

Full figure (34K)

Table 1 - Baseline characteristics of the patients randomized to receive narrowband UVB (TL-01) and selective broadband UVB (UV6).

Full table

Analysis

Number of exposures for clearance

The median number of exposures for clearance, based on fitting a Weibull distribution (Figure 3) and adjusting for stratification variables, was 28.4 for TL-01 and 30.4 for UV6 (ratio of the medians estimated as 0.93; 95% confidence interval (CI) 0.80, 1.09; P=0.39). The residual plots and Figure 3 indicated that the Weibull distribution provided a good fit for these data. The model also showed that patients with skin type III/IV cleared faster than those with skin type I/II (see Table 2 for details).

Figure 3.

Probability of non-clearance with the two lamps. Survival curves showing the probability of non-clearance of psoriasis during treatment with narrowband UVB (TL-01) (dashed lines) and selective broadband UVB (UV6) (solid lines). The stepped lines are Kaplan–Meier plots, with censored observations indicated by the small vertical tick marks. The smooth curves are fitted Weibull curves for each lamp, plotted at the mean values of the stratifying factors.

Full figure and legend (12K)

Table 2 - The effects of stratifying factors on the odds of clearance and the ratio of median number of exposures to clearance for all patients considered together irrespective of the lamp type used for treatment.

Full table

Cumulative dose for clearance

Based on fitting a Weibull distribution, the median (quartiles) of the cumulative dose to clearance, were estimated as 40.9 (28.1, 55.2) J/cm² (TL-01) and 39.9 (27.4, 53.6) J/cm² (UV6).

Clearance

Clearance of psoriasis was achieved in 28/50 (56%) of those receiving TL-01 compared with 20/50 (40%) of those receiving UV6. The odds ratio for clearance with TL-01 relative to UV6, adjusted for the factors used to stratify the allocation, was 2.00 (95% CI 0.87, 4.62), P=0.10. The odds of clearance with respect to the stratifying factors are shown in Table 2.

PASI scores in non-clearers

In order to see whether there was a difference in clinical response to the two lamp types in the patients who did not clear, we examined the last available psoriasis area and severity index (PASI) scores for all of the "non-cleared" patients, irrespective of the reason for non-completion. As this comparison involves groups not balanced by randomization, the baseline PASI scores for these patients were also analyzed to assess the comparability of the groups. The results are shown in Table 3. The corresponding comparisons among patients who failed to clear but made planned exits from the trial are also given in Table 3. It should be stressed that these are not randomized comparisons and should be interpreted with caution.

Table 3 - The mean PASI scores in non-clearing patients at baseline (before treatment) and based on the last score available for individual patients.

Full table

Side effects

A degree of erythema was noted at some stage in the treatment course in 43 patients treated with TL-01 and 42 treated with UV6. In only two patients treated with TL-01 and three treated with UV6 was the erythema of sufficient severity to cause them to miss treatments. Polymorphic light eruption occurred in three patients treated with TL-01, (two of whom withdrew as a result (Figure 2)) and in one patient treated with UV6. Pruritus occurred in two patients treated with UV6, and one withdrew as a result (Figure 2). Inflammatory psoriasis developed early in the course in one patient treated with each lamp type. Both patients withdrew (Figure 2) as topical corticosteroids were required to allow them to continue with phototherapy.

Follow-up

The number of patients remaining clear of psoriasis when examined 3 and 6 months after completing phototherapy is shown in Table 4.

Table 4 - Follow-up data showing the number of patients who remained clear of psoriasis 3 and 6 months after completing phototherapy with narrowband UVB (TL-01) and selective broadband UVB (UV6).

Full table

Discussion

In this randomized study, we have found no evidence of a difference between those treated with selective broadband UVB and those treated with narrowband UVB in terms of median number of treatments to clear, proportions of patients achieving clearance and improvement in PASI for non-clearers. The data are compatible with differences in treatment outcome described by the CIs given above. For the primary outcome, the median number of treatments to clear, the difference is likely to be less than 20%. Although this study is considerably larger than previous comparisons involving narrowband UVB, the CI for the ratio of the odds of clearing is quite wide.

The patients we studied were recruited from a phototherapy clinic where patients with psoriasis likely to require phototherapy are referred. Although the patients had relatively mild disease (as judged by the mean pretreatment PASI score), they are probably representative of patients with psoriasis receiving hospital-based phototherapy, particularly as a high proportion of eligible patients screened for inclusion actually entered the trial.

The two groups were well-matched in terms of baseline PASI score, and were stratified according to factors we anticipated might influence clearing. In fact, unlike in our previous studies (Gordon et al., 1999; Sakuntabhai et al., 1993), plaque size did not appear to influence outcome (Table 2), nor did involvement of the legs around or below the knees, an area usually considered fairly resistant to treatment (Waterston et al., 2004). However, patients of skin type III/IV had a significantly greater chance of clearing than those of skin type I/II.

We attempted to ensure that equal erythemal doses were given, irrespective of lamp type used for treatment, by measuring each patient's MED before commencement of the study (Gordon et al., 1998, 1999), and by using the same percentage-based dose increases. That 85% of patients developed erythema during the course of phototherapy suggests that our treatment doses were adequate. The clearance rate of 56% that we achieved with narrowband UVB is within the range of values reported in previous studies (29–90%) (Alora and Taylor, 1997; Dawe et al., 1998; Wainwright et al., 1998; Gupta et al., 1999; Leenutaphong et al., 2000; Yones et al., 2006). We were strict with regard to criteria by which patients were categorized as "clear" (see Materials and Methods). Nevertheless, the point at which "clearance" is achieved in an individual patient, or the sometimes used end point of "minimal residual activity", is subjective and imprecise. This underscores the need for the evaluating physician to be blinded to treatment allocation and treatment supervision, as was the case with our study. Our follow-up data (Table 4) show the disappointingly high relapse rate with UVB phototherapy, whichever lamp is used for treatment.

Although there have been a large number of small-scale studies comparing narrowband UVB and conventional broadband UVB (reviewed by Dawe, 2003), we are aware of only two studies involving selective UVB lamps (Karvonen et al., 1989; Storbeck et al., 1993). In one of these (Karvonen et al., 1989), all patients received dithranol in addition to UVB. In the other study (Storbeck et al., 1993), 10 patients with psoriasis received narrowband UVB to one-half of the body and broadband UVB (UV6) to the other side. In eight of the patients a better response was noted with narrowband UVB, but the study was terminated whenever a difference between the two sides of the body was noted, rather than at clearance, and the mean number of exposures was only 10.

Parrish and Jaenicke (1981), in their seminal work on the action spectrum for clearance of psoriasis, found that wavelengths less than 290 nm, whilst highly erythemogenic, were not effective in clearing psoriasis. The authors also suggested that these findings could account for the improved effectiveness of selective compared with conventional broadband UVB phototherapy. The TL-12 lamp, as an example of a conventional broadband UVB, emits 5.5% of its output at less than 290 nm, compared with 0.5% for UV6 and 0.1% for TL-01 (Ibbotson et al., 2004). When the lamps' spectra are weighted according to the erythema action spectrum (McKinlay and Diffey, 1987), the contribution to erythema from radiation <290 nm is 21.8% (TL-12), 6.9% (UV6), and 2.3% (TL-01). We described previously (Diffey and Farr, 1987) a "phototherapy index", based on the Parrish and Jaenicke (1981) action spectrum, which gave the predicted efficacy of different lamp types at treating psoriasis (an index <1 indicated that doses greater than the MED would be required to clear psoriasis, whereas an index >1 indicated that clearance could be achieved with suberythemal doses). For minimal erythema treatment doses, the calculated phototherapy indices were 0.6 (conventional broadband), 1.3 (selective broadband), and 1.5 (narrowband) (Diffey and Farr, 1987; Diffey, 1990). It should be pointed out that the action spectrum for clearance of psoriasis, and any predictions based upon it, are subject to a good deal of uncertainty as Parrish and Jaenicke (1981) only studied four patients, and some of these appeared treatment resistant. Nevertheless, the results of our clinical study showing no evidence of a difference in response between selective broadband UVB and narrowband UVB are in keeping with the findings of Parrish and Jaenicke (1981).

The risks of narrowband UVB phototherapy will only become apparent when long-term follow-up studies become available, as was the case with psoralen photochemotherapy (Stern and Lange, 1988). Presently available follow-up data (Weischer et al., 2004; Man et al., 2005) are of too short duration to contribute. Until clinical data become available, the only method of risk estimation is to use the human photocarcinogenesis action spectrum (CIE, 2006) derived from modified murine experimental data. Based on this action spectrum, relative to a conventional broadband UVB source (FS20, TL-12), the selective broadband source (UV6) has a carcinogenic potential that is 1.5 times greater, whereas the narrowband UVB lamp is 2.3 times more carcinogenic per MED; a figure in keeping with the estimate given by Young (1995). The choice of lamp for UVB phototherapy should be based on assessments of efficacy and potential long-term hazards of treatment. Conventional broadband lamps, although potentially safer, are probably of insufficient efficacy to be recommended. Narrowband UVB lamps (TL-01) although effective, are potentially 50% more carcinogenic for equal erythemal doses than selective broadband lamps (UV6). Any increased carcinogenic risk is of concern given the tendency of psoriasis to relapse rapidly after UVB clearance (Table 4) (Yones et al., 2006) and the need for repeated courses of treatment. If these two lamp types are equally effective, or even if the selective broadband source is slightly less effective at achieving clearance (as our results possibly indicate), the selective broadband lamp may provide the best balance between safety and efficacy for routine clinical use.

Materials and Methods

Protocol and study design

This was a single-center, observer-blinded, randomized study to compare response of psoriasis to phototherapy using selective broadband UVB (UV6, Sylvania, Raunheim, Germany) (Figure 1) or narrowband UVB (TL-01). The study was approved by the Newcastle and North Tyneside Local Research Ethics Committees, registered as a clinical trial (ISRCTN61943529, http://www.controlled-trials.com), conducted in accord with the Declaration of Helsinki Principles, and participants gave written, informed consent. Sample size estimation, as reported previously (de Berker et al., 1997), suggested that for 80% power to detect a difference in median number of treatments to clearance of 25% at the 5% significance level, two groups of 50 patients would be required.

Patients

Patients with plaque-type psoriasis were recruited (by P.M.F.) from a dedicated phototherapy clinic at a University Teaching Hospital. All patients considered for UVB treatment of psoriasis were screened for inclusion in the trial. The minimum age of entry was 18 years and patients were excluded if they had received phototherapy or systemic agents for psoriasis in the preceding 3 months.

UV phototesting and treatment

The MED for the appropriate lamp type was measured in each patient. Phototesting was performed on the volar aspect of the forearm using a device (Gordon et al., 1998) that allowed the simultaneous delivery of 10 doses from either the TL-01 or UV6 lamp in a geometric series ranging from 0.2 to 1.6 J/cm². The MED, defined as the smallest dose of radiation required to achieve just detectable erythema, was judged visually 24 hours after irradiation.

Patients were treated three times weekly with whole body exposure units (UV7001, Waldmann, Villingen-Schwenningen, Germany) fitted with 40 fluorescent lamps. The initial treatment dose was 70% of the MED and the dose was increased after alternate treatments by 40%, decreasing stepwise to 5% by the 18th treatment. If erythema developed during treatment, depending on the severity, planned dose increments were postponed or treatments missed, until the erythema resolved. Emollients only were permitted during the trial.

Dosimetry

Measurements of irradiance were made with a radiometer (IL 700, International Light, Newburyport, MA) and UVB sensor, calibrated spectroradiometrically, and statements of dose refer to unweighted, spectrally integrated radiant exposure between 250 and 400 nm.

Assignment

Allocation of patients to treatment was stratified by three prognostic factors namely:

1. predominant plaque size – defined as small (<3 cm diameter) or large (>3 cm) (Gordon et al., 1999);
2. involvement of skin on the legs around or below the knees (yes/no);
3. skin type (I/II or III/IV).

Treatment allocation used opaque, sequentially numbered, sealed envelopes (assembled by J.N.S.M.) and was based on randomized permuted blocks within strata, with block lengths randomly chosen as four or six. Envelopes were opened by phototherapy nursing staff (supervised by S.L.) who then administered the assigned treatment. Patients were aware of the treatment they were receiving.

Assessments and masking

Clinical assessments of each patient were made immediately before commencement of the course of phototherapy and then after every six treatments (2 weeks) by a clinician (S.M.K.) who was blinded to treatment allocation. These assessments were organized and supervised by nursing staff, and the assessing clinician was only permitted to judge clearance and grade the psoriasis severity using the PASI scores (Fredriksson and Pettersson, 1978). Clearance was defined as no residual psoriasis, or psoriasis only remaining in areas shaded from UV exposure such as flexures. All clinical supervision of the patients was carried out by phototherapy nurses and the supervising dermatologist (P.M.F.). The primary hypothesis was to compare the lamps with respect to the number of treatments to clearance, and this was the primary outcome measure. Secondary outcomes were clearance of psoriasis and PASI scores for non-clearing patients. Patients who cleared during the study were followed up at 3 and 6 months and assessed for continued clearance or relapse.

Patients were encouraged to continue for at least 16 treatments before a decision was made about lack of effectiveness of the treatment, at which planned withdrawal was permitted. No maximum number of treatments was specified for the trial patients, but the phototherapy nurses followed a standard protocol requiring evidence of continuing improvement to allow treatment to continue beyond a total of 36 exposures. Patients who cleared, and those who did not clear but received at least 16 exposures, were judged to have completed the trial. Any patient making a non-planned exit from the trial (by failing to attend for treatment), or those who discontinued because of side effects were recorded as "failure to complete".

Statistical analysis

The principal analyses compare the treatment groups as formed by randomization: patients who failed to complete were grouped with those who failed to clear. The primary outcome variable was the number of visits to clearance and this together with the cumulative UV dose for clearance were analyzed assuming a Weibull proportional hazards survival model, with outcomes being the number of exposures for clearance and cumulative UV dose for clearance, with patients whose psoriasis did not clear considered to be censored observations. The assumption of a Weibull distribution was assessed by means of residual plots (Aitkin and Clayton, 1980) and by superimposing fitted survival curves with distribution-free estimators. Whether or not a patient cleared was analyzed using logistic regression. All models included allocated treatment and the stratification variables and were fitted using R (R Development Core Team, 2005) and the R survival package. The PASI scores in non-clearing patients were compared between treatments using t-tests.

Conflict of Interest

The authors state no conflict of interest.

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