Ann Dermatol.  2009 May;21(2):136-141. 10.5021/ad.2009.21.2.136.

Comparative Study of the Gross Interpretation of Phototesting and Objective Measurement with Using a Spectrophotometer for Patients with Psoriasis and Vitiligo Treated with Narrow-band UVB

• Choi KW
• Kim KH
• Kim YH

• KMID: 2219381
• DOI: http://doi.org/10.5021/ad.2009.21.2.136

Abstract

BACKGROUND
Determination of the minimal erythema dose (MED) is important for developing a phototherapy protocol and to diagnosis photosensitivity disorders. But obtaining a precise and reproducible MED is quite difficult because a phototest for erythema is based on subjective assessment.
OBJECTIVE
The objective of our study was to compare the gross interpretation of a phototest and the objective measurement using a spectrophotometer for determining the parameters of cutaneous narrow-band UVB (NBUVB) therapy.
METHODS
A total of 14 psoriasis and 10 vitiligo patients who receiving NBUVB phototherapy with skin types III and IV were selected for this study. To perform phototesting, ten sites on the skin of the back were vertically exposed to a series of 10 NBUVB doses among 14 doses between 340 and 1,400 mJ/cm2. We interpreted the gross findings of erythema and measured the L*a*b* values with using a spectrophotometer at each phototest spot and at the control skin. Also, we evaluate the relationship between the gross presentation and the spectrophotometric analysis by delta E for the assessment of the minimal perceptible erythema (MPE) and MED.
RESULTS
For all the subjects, the MEDs were measured in the 490~1,000 mJ/cm2 range. The average of the colorimetric values for the control skin were L*: 64.8, a*: 7.9 and b*: 19.8. Among them, the L* value and MED value were shown to be inversely correlated, and as the L* value was decreased, the MED was increased. For the MPE, the delta E, which was the color difference of the normal skin and the phototest area, was within the range of 1.5~3.0 in 17 of the 21 patients, and 4 patients were within the range of 1.0~1.5. For the MED, among the 21 patients, the delta E of 17 patients was within the range of 3.0~6.0, and 4 patients were within the range of 6.0~12.0.
CONCLUSION
A spectrophotometer enables UV erythema to be assessed objectively and quantitatively, and this can compensate for the disadvantages of subjective gross interpretation when determining the MED. Delta E is a good novel and objective indicator for determining the MPE and MED. So, a spectrophotometer is a very useful instrument for developing a phototherapy protocol for psoriasis and other dermatoses and for making the diagnosis of photosensitivity disorders.

Keyword

Delta E; Minimal erythema dose (MED); Narrow-band UVB (NBUVB); Psoriasis; Spectrophotometer; Vitiligo

MeSH Terms

Erythema
Humans
Photosensitivity Disorders
Phototherapy
Psoriasis
Skin
Skin Diseases
Vitiligo

Figure

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  Fig. 1 Spectrophotometer CM-2006d (Minolta Co. Ltd, Osaka, Japan).

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  Fig. 2 The distribution of the NBUVB MED.

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  Fig. 3 Correlation between the spectrophotometric values and the MED of the NBUVB.

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  Fig. 4 Correlation between the delta E values and the MPE of the NBUVB.

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  Fig. 5 Correlation between the delta E values and the MED of the NBUVB.

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