Comment
Comparisons to Prior Studies—This study confirmed that phototherapy is equally effective for older and younger adults, with approximately 90% reaching medium to high clearance levels with approximately 35 treatments in both groups. Prior studies of all age groups found that patients typically cleared with an average of 20 to 28 treatments.7,8,14-16 In contrast, the findings in older adults from this study were similar to the older adult study from the United Kingdom that reported a 91% clear/near clear rate with an average of 30 treatments.17 The clearance level also was similar to the older adult study in Turkey18 that reported 73.7% (70/95) of patients with psoriasis achieved a minimum psoriasis area severity index of 75, indicating 75% improvement from baseline.
Impact of Photosensitizing Medications on Clearance—Photosensitizing medications and treatment frequency were 2 factors that might explain the slower clearance rates in younger adults. In this study, both groups of patients used similar numbers of photosensitizing medications, but more older adults were taking 3 or more medications (Table 3). We found no statistically significant relationship between taking photosensitizing medications and either the clearance rates or the level of clearance achieved in either age group.
Impact of Treatment Frequency—Weekly treatment frequency also was examined. One prior study demonstrated that treatments 3 times weekly led to a faster clearance time and higher clearance levels compared with twice-weekly treatment.7 When patients completed treatments twice weekly, it took an average of 1.5 times more days to clear, which impacted cost and clinical resource availability. The patients ranged in age from 17 to 80 years, but outcomes in older patients were not described separately.7 Interestingly, our study seemed to find a difference between age groups when the impact of treatment frequency was examined. Older adults completed nearly 4 fewer mean treatments to clear when treating less often, with more than 80% achieving high levels of clearance, whereas the younger adults required almost 7 more treatments to clear when they came in less frequently, with approximately 80% achieving a high level of clearance. As a result, our study found that in both age groups, slowing the treatment frequency extended the treatment time to clearance—more for the younger adults than the older adults—but did not significantly change the percentage of individuals reaching full clearance in either group.
Erythema Rates—There was no association between photosensitizing medications and erythema rates except when patients were taking at least 3 medications. Most medications that listed photosensitivity as a possible side effect did not specify their relevant range of UV radiation; therefore, all such medications were examined during this analysis. Prior research has shown UVB range photosensitizing medications include thiazides, quinidine, calcium channel antagonists, phenothiazines, and nonsteroidal anti-inflammatory drugs.19 A sensitivity analysis that focused only on these medications found no association between them and any particular grade of erythema. However, patients taking 3 or more of any medications listing photosensitivity as a side effect had an increased risk for grade 2 erythema.
Erythema rates in this study were consistent with a 2013 systematic review that reported 57% of patients with asymptomatic grade 1 erythema.25 In the 2 other comparative older adult studies, erythema rates varied widely: 35% in a study from Turkey18compared to only1.89% in a study from the United Kingdom.17
The starting dose for NB-UVB may drive erythema rates. The current study’s protocols were based on an estimated MED that is subjectively determined by the dermatology provider’s assessment of the patient’s skin sensitivity via examination and questions to the patient about their response to environmental sun exposure (ie, burning and tanning)26 and is frequently used to determine the starting dose and subsequent dose escalation. Certain medications have been found to increase photosensitivity and erythema,20 which can change an individual’s MED. If photosensitizing medications are started prior to or during a course of NB-UVB without a pretreatment MED, they might increase the risk for erythema. This study did not identify specific erythema-inducing medications but did find that taking 3 or more photosensitizing medications was associated with increased episodes of grade 2 erythema. Similarly, Harrop et al8 found that patients who were taking photosensitizing medications were more likely to have grade 2 or higher erythema, despite baseline MED testing, which is an established safety mechanism to reduce the risk and severity of erythema.14,20,27 The authors of a recent study of older adults in Taiwan specifically recommended MED testing due to the unpredictable influence of polypharmacy on MED calculations in this population.28 Therefore, this study’s use of an estimated MED in older adults may have influenced the starting dose as well as the incidence and severity of erythemic events. Age-related skin changes likely are ruled out as a consideration for mild erythema by the similarity of grade 1 erythema rates in both older and younger adults. Other studies have identified differences between the age groups, where older patients experienced more intense erythema in the late phase of UVB treatments.22,23 This phenomenon could increase the risk for a grade 2 erythema, which may correspond with this study’s findings.
Other potential causes of erythema were ruled out during our study, including erythema related to missed treatments and shielding mishaps. Other factors, however, may impact the level of sensitivity each patient has to phototherapy, including genetics, epigenetics, and cumulative sun damage. With NB-UVB, near-erythemogenic doses are optimal to achieve effective treatments but require a delicate balance to achieve, which may be more problematic for older adults, especially those taking several medications.