Ann Dermatol.  2014 Feb;26(1):17-25. 10.5021/ad.2014.26.1.17.

Spectrophotometric Measurement of Minimal Erythema Dose Sites after Narrowband Ultraviolet B Phototesting: Clinical Implication of Spetrophotometric Values in Phototherapy

Affiliations
  • 1Department of Dermatology, Dong-A University College of Medicine, Busan, Korea. khkim@dau.ac.kr
  • 2Department of Dermatology, Sorokdo National Hospital, Goheung, Korea.

Abstract

BACKGROUND
The spectrophotometer is well known to be a useful tool for estimating the objective minimal erythema dose (MED) during planning of phototherapy protocol. However, only a few spectrophotometric values are used to evaluate the erythema and pigmentation of the MED site during phototesting.
OBJECTIVE
To determinea new meaning of the relationships among spectrophotometric values during phototesting.
METHODS
Twenty-five patients with psoriasis and 23 patients with vitiligo were selected before undergoing narrowband ultraviolet B phototherapy. We interpreted the gross findings of erythema and measured the L*a*b* values using a spectrophotometer at each phototest spot. We compared MEDs, basic spectrophotometric values (L*a*b*), and b*/L* values separately according to skin type, and determined the correlation of each spectrophotometric value and the correlation between a* and b*/L* values.
RESULTS
Among L*a*b* values, only b* values showed a statistically significant difference between the type III and IV groups (p=0.003). There was a positive correlation only between MEDs and b* values (p<0.05). The average b*/L*value in the type IV group was significantly higher than the type III group (p<0.05).
CONCLUSION
The higher b* values in type IV skin indicates that skin tanning develops more prominently than type III. The correlation between MEDs and b* values may signify that the skin pigmentation status is deepened with the higher MEDs. The difference in b*/L*values between type III and IV skin reflects that the b*/L*value is thought to be an index of tanning. The a* value, known as an index of erythema, does not influence the degree of tanning.

Keyword

a*value; L*value; Skin phototype; Spectrophotometer

MeSH Terms

Erythema*
Humans
Phototherapy*
Pigmentation
Psoriasis
Skin
Skin Pigmentation
Tanning
Triacetoneamine-N-Oxyl
Vitiligo
Triacetoneamine-N-Oxyl

Figure

  • Fig. 1 The distribution of minimal erythema dose (MED)-narrowband ultraviolet B (NBUVB) in all the patients.

  • Fig. 2 The average spectrophotometric values measured at minimal erythema dose sites in skin type III and skin type IV (A: L* value; B: a* value; C: b* value). Only b* value shows statistically significant difference between the type III and IV groups (p=0.003). †Classification according to the standard of Fitzpatrick skin type III, IV.

  • Fig. 3 A correlation between each L*, a*, b*, and minimal erythema dose (MED) values. (A) L* value=60.30±2.95, range 52.16~64.89. (B) a* value=12.57±1.60, range 9.53~16.42. (C) b* value=18.80±1.70, range, 14.31~23.64. Only correlation between b* and MED values show significant correlation (p<0.05).

  • Fig. 4 Significant correlation in a*L* curve (A, p<0.05). Although the b*L* curve and the b*a* curve seem to show significant correlation, but no significant correlation is shown in the b*a* curve or b*L* curve (B and C, p<0.05, respectively). †Classification according to the standard of Fitzpatrick skin type III, IV.

  • Fig. 5 The differences of b*/L* values between skin types III and IV depending on the ranges of delta E (A: <3.0; B: 3.0~6.0: C, >6.0). All data show statistically significant difference (p<0.05). †Classification according to the standard of Fitzpatrick skin type III, IV.

  • Fig. 6 A correlation between a* and b*/L* depending on (A) the delta E value and (B) in skin types. Correlation between a* values and b*/L* in skin type III and IV showed no significant correlation. †Classification according to the standard of Fitzpatrick skin type III, IV.


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