Aesth. Plast. Surg. 25:129–133, 2001
DOI: 10.1007/s002660010109© 2001 Springer-Verlag New York Inc.

Usefulness of a Narrow-Band Reflectance Spectrophotometer in Evaluating
Effects of Depigmenting Treatment
Kotaro Yoshimura, M.D., Kiyonori Harii, M.D., Yuji Masuda, B.S., Motoji Takahashi, Ph.D., Takao Aoyama, Ph.D.,
and Tatsuji Iga, Ph.D.
Tokyo, Japan
Abstract. As a depigmenting treatment, combined topical applications of all-trans retinoic acid (atRA) aqueous gel and 5%hydroquinone, 7% lactic acid ointment were used for Oriental
patients with hyperpigmented skin lesions such as senile lentigines and nevus spilus. A narrow-band reflectance spectrophotometer and a tristimulus colorimeter were used to evaluate
objectively the intensity of pigmentation and erythema at eachclinical visit. L*, a*, and b* values measured with a tristimulus
colorimeter (Chroma Meter CR-300) enabled the evaluation oferythema but not pigmentation. On the other hand, the melaninand hemoglobin values measured with a narrow-band reflectance spectrophotometer (Mexameter MX-16) expressed botherythema and pigmentation well. It was revealed that, in ourbleaching protocol, the narrow-band reflectance spectrophotometer was quite useful for estimating accurately the intensityof pigmentation and erythema and determining the best time
point for the cessation of atRA treatment.
Key words: Depigmenting treatment—Retinoic acid aqueous
gel—Senile lentigines—Nevus spilus

Using our bleaching protocol with a high concentrationof all-trans retinoic acid (atRA) aqueous gel in combination with hydroquinone and lactic acid, a remarkable
improvement of various skin lesions with hyperpigmentation, such as senile lentigines [13], melasma, postinflammatory hyperpigmentation, and nevus spilus, wasobtained with a short period of treatment [14]. However,during the treatment, side effects such as erythema were
frequently observed after the topical application of atRA.

Correspondence to K. Yoshimura, M.D., Department of Plastic
and Reconstructive Surgery, University of Tokyo, 7-3-1,
Hongo, Bunkyo-Ku, Tokyo 113-8655, Japan

Tristimulus colorimeters and full-range or narrowband spectrophotometers have been employed for thequantification of erythema and pigmentation induced byultraviolet radiation (UVR) [7], and for the color analysis
of skin lesions [9] or transferred skin [12]. We have useda tristimulus colorimeter and a narrow-band spectrophotometer to evaluate skin reactions such as the intensity ofpigmentation and erythema in our bleaching treatment.
Representative cases are demonstrated and the usefulness of the reflectance spectrophotometer is discussed.
Methods
Combined topical applications of atRA, hydroquinone,
and lactic acid were used for skin lesions with hyperpigmentation. atRA aqueous gel (atRA gel; 0.1, 0.2, and0.4%) was originally prepared at the Department of Pharmacy, University of Tokyo. AtRA gel was topically applied together with 5% hydroquinone, 7% lactic acidointment (HQ-LA ointment), also prepared as describedabove. Plastibase (petrolatum polyethylene ointmentbase; Taisho Pharmacology, Osaka, Japan) was used as
the ointment base of HQ-LA ointment. Both atRA gel
and HQ-LA ointments are pharmacologically unstable,
so that fresh ointments were prepared at least once amonth. Each ointment was topically applied under signed
informed consent to more than 120 Oriental patients withhyperpigmented skin lesions such as sinile lentigines,
melasma, postinflammatory hyperpigmentation, and nevus spilus.
Treatment protocol. atRA gel was applied to the skinlesions twice a day, followed by the application of HQLA ointment. The concentration of atRA gel waschanged according to the treated site: 0.1% atRA gel forthe face, 0.2% for the trunk and upper extremities, and
0.4% for the lower extremities. In the daytime, a broad-130

Evaluating Effects of Depigmenting Treatment

Fig. 1. (A) The tristimulus colorimeter (Chroma Meter CR-300). The control unit has a small printing unit and is connected to ameasuring probe. This instrument offers five color systems for the data display including the CIE L*a*b* system. (B) The
narrow-band reflectance spectrophotometer (Mexameter MX-16). The foot-switch model enables measurement without applying
pressure to the skin. The melanin and hemoglobin values appear in the display of the control unit.

spectrum sunscreen cream was concomitantly applied
throughout the treatment period. After improvement of
the hyperpigmentation was obtained, the application of
atRA was discontinued, and topical application of corticosteroids (0.12% dexamethasone ointment) for 1 to 4
weeks was started to reduce the reactive erythema andinflammation. Throughout the therapy, topical application of HQ-LA ointment was continued except for cases
in which erythema was not reduced after a few weeks’application of corticosteroid and HQ-LA ointment.
Measurement of skin color. As an objective measurement of the color of the designated lesion and normalskin, two types of portable reflectance instruments, a
tristimulus colorimeter and a narrow-band reflectancespectrophotometer, were used at each clinical visit. During both measurements the photoreceivers were placed
perpendicularly on the skin with minimal pressure. Eachspot was measured three times and the average of thethree measured values was calculated.
Instrumentation. Chroma Meter CR-300 (Minolta,
Osaka, Japan) was used for colorimetry. L*, a*, and b*
values of the CIE (Commission Internationale del’Eclairage) system were measured. A color is expressedin a three-dimensional coordinate system with an a* axis
(green–red), a b* axis (yellow–blue), and an L* axis
(white–black) (see Refs. 1 and 4 for details). The L*
value gives the relative brightness (or luminance), ranging from total black (L* ⳱ 0) to total white (L* ⳱ 100).
a* is the component of separation between red (positive
value) and green (negative value). b* represents the balance between yellow (positive) and blue (negative). The
instrument consists of a control unit and a measuringprobe for illuminating an area 8 mm in diameter (Fig.
1A). The measuring probe has a pulsed xenon lamp thatemits an intense white light covering the entire visible
spectrum (Chroma meter CR-300 instruction manual).
The color of the reflected light is analyzed by three high-sensitivity silicone photocells that are filtered to matchthe CIE standard observer curves for the primary colors:
blue (450 nm), green (550 nm), and red (610 nm).
The Mexameter MX 16 (Courage+Khazaka ElectricGmbH, Köln, Germany) was used for spectrophotometry. Because the original model employs a measuringprobe that is placed on the spot to be measured withslight pressure, we ordered a foot-switch model withwhich measuring can be preformed without applying any
pressure (Fig. 1B). A measuring probe with a measuring
area of 5-mm diameter emits light of three predefined
wavelengths (568 nm, green; 660 nm, red; and 880 nm,
infrared) and measures the light reflected by the skin.
The melanin value is measured using 2 wavelengths (660
and 880 nm) to achieve different absorption rates by themelanin granules. For the hemoglobin measurement as
well, two wavelengths (568 and 660 nm) are used. The
melanin and hemoglobin values are calculated as follows.
Melanin value = 500Ⲑlog5 × [log (infrared-reflectionⲐ
red-reflection) + log5]
Hemoglobin value = 500Ⲑlog5 × [log (red-reflection/
green-reflection) + log5]
Evaluation of treatment effects. The difference in theabsolute melanin value between a skin lesion and normalskin is referred to as the relative melanin value (RMV) of
the skin lesion in this paper, which indicates the intensityof pigmentation relative to the surrounding normal skin.
RMV was calculated as
RMV ⳱ AMV(lesion) − AMV(normal)
where AMV(lesion) and AMV(normal) are the absolutemelanin values of a skin lesion and the surrounding normal skin, respectively.
In the same manner, the differences in the absolutehemoglobin values and the L*, a*, and b* values areK. Yoshimura et al.

131

Fig. 2. (A) A pretreatment view of a 49-year-old woman with two senile lentigines on her right cheek. RMV ⳱ 47.7, RHV ⳱ 24.3,(−)⌬L* ⳱ 48.5, ⌬a* ⳱ 20.6, ⌬b* ⳱ −1.5. (B) After treatment for 3 weeks. Although moderate erythema was seen, pigmentation
was reduced objectively and clinically. The topical application of atRA was discontinued. RMV ⳱ −3.0, RHV ⳱ 89.3, (−)⌬L* ⳱
38.6, ⌬a* ⳱ 41.6, ⌬b* ⳱ −12.1. (C) After treatment for 10 weeks. The erythema was almost undetectable clinically. RMV ⳱ −3.7,
RHV ⳱ 33.3, (−)⌬L* ⳱ 10.5, ⌬a* ⳱ 13.2, ⌬b* ⳱ −11.9.

normal skin in Japanese and the RMV of hyperpigmented lesions are usually 460–500 and 20–120, respectively. A RMV of 5 or less is difficult to recognize clinically.
Case Reports

Fig. 3. Sequential changes in RMV, RHV, (−)⌬L*, ⌬a*, and⌬b* of case 1. (−)⌬L* was plotted instead of ⌬L* for easiercomparison to RMV.

designated RHV, ⌬L*, ⌬a*, and ⌬b*, respectively, andcalculated as described below:
RHV = AHV(lesion) − AHV(normal)⌬L* = L*(lesion) − L*(normal)⌬a* = a*(lesion) − a*(normal)⌬b* = b*(lesion) − b*(normal)
A negative RMV means that the measured spot islighter than the control. The absolute melanin value ofCase 1. A 49-year-old woman with two sinile lentigines
on her right cheek underwent combined topical applications of 0.1% atRA gel and HQ-LA ointment (Fig. 2A:
before treatment). The sequential changes in RMV,
RHV, ⌬L*, ⌬a*, and ⌬b* are demonstrated in Fig. 3. On
day 7 scaling was seen, and RMV was considerably reduced after the first 2 weeks, resulting in a negative
RMV, while RHV was increased. Since an improvementof pigmentation was recognized objectively and clinically, atRA gel was discontinued despite the moderate
erythema in the treated region (Fig. 2B: at 3 weeks).
Corticosteroid was then applied topically for 4 weeks.
Meanwhile, RHV gradually decreased and RMV remained around 0. Three weeks after the discontinuationof corticosteroid treatment, the erythema disappeared almost completely and RHV was reduced almost to thelevel before treatment (Fig. 2C: at 10 weeks). HQ-LA
ointment was applied throughout the treatment for 10
weeks. The RMV before treatment was 47.7, and thefinal RMV after 10 weeks of treatment was −3.7. ⌬a*changed very similarly to RHV, while ⌬b* did notchange significantly throughout the treatment. (−)⌬L*,
which is the negative value of ⌬L*, was slightly elevatedduring the first 2 weeks and then gradually decreased.

132

Evaluating Effects of Depigmenting Treatment

Fig. 4. A A pretreatment view of a 19-year-old man withcongenital nevus spilus on his left shoulder. RMV ⳱ 35.3,
RHV ⳱ 13.7, (−)⌬L* ⳱ 35.7, ⌬a* ⳱ 9.0, ⌬b* ⳱ −10.4. B
After treatment for 2 weeks. Severe erythema was observed in
the treated area. RMV ⳱ −15.3, RHV ⳱ 75.0, (−)⌬L* ⳱ 53.5,⌬a* ⳱ 45.1, ⌬b* ⳱ −13.5. C After treatment for 10 weeks.
Pigmentation and erythema had almost disappeared. RMV ⳱−4.0, RHV ⳱ 25.3, (−)⌬L* ⳱ 8.20, ⌬a* ⳱ 10.5, ⌬b* ⳱−10.1.

applied for 3 weeks, followed by HQ-LA ointment application alone. Meanwhile, RHV was reduced gradually, while RMV was slightly elevated, presumably
because of the temporary postinflammatory hyperpigmentation. At 5 weeks after the discontinuation of corticosteroid, the erythema had almost disappeared (Fig.
4C: after 10 weeks). The RMV before treatment was
35.3, and the final RMV after 10 weeks of treatment was−4.0. The sequential change in ⌬a* was quite similar tothat of RHV, and ⌬b* was constant throughout the treatment period. (−)⌬L* increased a little during the first 2
weeks and gradually decreased after 2 weeks.
Fig. 5. Sequential changes in RMV, RHV, (−)⌬L*, ⌬a*, and⌬b* of case 2.

Case 2. A 19-year-old man with congenital nevus spilus
on his left shoulder underwent combined topical applications of 0.2% atRA gel and HQ-LA ointment (Fig. 4A:
before treatment). The sequential changes in RMV,
RHV, ⌬L*, ⌬a*, and ⌬b* are demonstrated in Fig. 5. On
day 5 scaling was seen, and at 2 weeks atRA gel was
discontinued because RMV was reduced to a negativevalue. At that time, RHV was elevated to 75 and erythema was severe, so that it was not easy to estimate theextent of improvement of the pigmentation (Fig. 4B: at 2
weeks). HQ-LA ointment and corticosteroid were thenDiscussion
We have been successfully using high concentrations of
atRA aqueous gel combined with hydroquinone and lactic acid as a depigmenting treatment for hyperpigmented
skin lesions. In our protocol, aggressive retinoid treatment followed by the suppression of erythema and inflammation with corticosteroid can considerably shorten
the treatment time and lead to satisfactory clinical results[14].
In this protocol, after a few weeks of treatment with
atRA gel and HQ-LA ointment, hyperpigmentation wasmarkedly reduced, frequently even resulting in a negative value of RMV. However, as shown in Figs. 2B and
4B, moderate to severe erythema was usually observed inK. Yoshimura et al.

the treated areas. It is hard to evaluate clinically the
improvement of pigmentation with accuracy when thelesion is overlaid with erythema. It is quite important inour depigmenting protocol to measure the intensity ofpigmentation and erythema, not only to estimate the effect of the treatment but also to determine when atRA gel
application should be discontinued and corticosteroid
should be started. Although typical clinical time courses
are demonstrated in Figs. 2A–C and 4A–C, it may benecessary to modify the protocol in cases in which thepigmentation is not improved adequately after a few
weeks of atRA treatment. The objective measurement ofpigmentation and erythema was invariably a great help in
deciding the treatment appropriate to the individual clinical situation.
In normal skin, the a* value showed a strong linear
correlation with the erythema index of the spectrophotometer [11]. Similarly, a* showed a sequential change
approximately parallel to that of RHV in our treatment(Figs. 3 and 5).
Although Seitz and Whitmore [10] suggested that theb* value was a good indicator of tanning, a recent study[7] disputed the correlation between the b* value and themelanin index. In Figs. 3 and 5, ⌬b* showed a smallchange during our treatment, and it is suggested that theb* value is not greatly affected by either pigmentation orerythema.
In a number of previous studies [2,3,5,6,8], the L*
value has been utilized as an index of skin pigmentation.
However, there was only a weak correlation between theL* value and the melanin index detected in normal skin[7]. For easier comparison between the sequentialchanges in RMV and ⌬L* during our treatment, (−)⌬L*
was plotted in this paper. Figures 3 and 5 suggest that(−)⌬L* was affected by both pigmentation and erythema.
After a few weeks of treatment, although RMV wasmarkedly reduced and the pigmentation was clinicallyreduced, (−)⌬L* did not decrease or, rather frequently,
increased. (−)⌬L* as well as ⌬a* was elevated whenerythema progressed, although RMV was reduced andappeared to keep indicating the intensity of pigmentation. It is therefore concluded that the L* value is not anappropriate index for pigmentation, especially when erythema is involved during treatments such as ours.
Although the CIE L*a*b* system has been widelyused in a number of fields, it is hard to estimate theintensity of pigmentation with L*, a*, and b* values, but
the narrow-band spectrophotometer was quite useful forthat purpose, even when the pigmented lesions wereoverlaid with erythema.
Conclusion
Combined topical applications of all-trans retinoic acidaqueous gel and 5% hydroquinone, 7% lactic acid ointment have been successfully used as a depigmenting
treatment for hyperpigmented skin lesions such as senile
lentigines and nevus spilus. Although it was hard to133translate the L*, a*, and b* values measured with a colorimeter to the intensity of pigmentation, a narrow-bandreflectance spectrophotometer that measures the melaninand hemoglobin indices was found to be quite useful for
estimating accurately the intensity of pigmentation anderythema and determining when the application of atRA
treatment should be discontinued.
Acknowledgments. We express our sincere appreciation to
Yuka Kuwahara and Takako Kato for their assistance in colorimetric measurement.

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