Influence of PUVA therapy on dermoscopic features of acquired melanocytic nevi

ARTICLE

Auteur(s) : Emine DERVIS, Kadriye KOC, Aynur KARAOGLU

Department of Dermatology, Haseki General Hospital, Sarigöl Laleli Cad. No:3/3, Gaziosmanpasa, Istanbul-Turkey

Article accepted on 29/04/2004

UV Radiation (UVR) is the main cause of epithelial skin cancers, although its exact role in the development of benign and malignant melanocytic skin tumors remains unclear [1].

The combination of psoralens plus ultraviolet A (PUVA) has been used in the treatment of many skin diseases since its introduction in 1974. It was approved by FDA in 1982 in the treatment of severe psoriasis [2]. For the first time in 1975/ 1976, Stern et al., in a prospective study, followed up yearly a total of 1380 psoriatic patients under PUVA treatment in 16 university centers. As a result, they showed that about 15 years after the first treatment of PUVA and especially in a patient who had received ≥ 250 PUVA treatments, the risk of malignant melanoma increased [3]. In their latest report published in 2001, Stern et al. found that, since 1975, 23 patients have developed 26 invasive or in situ cutaneous melanomas. They emphasized that the risk is greater in patients exposed to high doses of PUVA and appears to be increasing with time [4]. However, Swedish PUVA follow-up studies on PUVA failed to show an increased risk for the development of melanoma during an average follow-up of between 15 and 16 years [5].

Several studies have showed that UV radiation can produce clinical, histologic and ultrastructural changes in melanocytic nevi [6-9]. Dermoscopy is an in vivo technique that enables the clinician to visualize a variety of structures in pigmented cutaneous lesions that are not discernible by naked-eye examination. We investigated whether PUVA therapy which is used to treat skin diseases can change the dermoscopic appearance of acquired melanocytic nevi.

Patients and methods

Six female and eight male patients with a mean age of 30.71 year (range 17 to 45 years) who were about to undergo PUVA therapy for any reason were enrolled in the study.
Two morphologically similar melanocytic nevi (n:28) from 14 patients with a diameter of < 6 mm. and no suspicion of malignancy on clinical and surface microscopic investigation were selected for the study. All nevi were located on the trunk.
UVA radiation was given with Dermalight 6000 device (Dr. K.Hönle GmbH, Germany) two hours after taking 8-methoxypsoralen (0.6 mg/kg) orally. The initial dose was equal to a standard dose as a base suitable to skin type according to Melski et al. [10]. In each patient, one nevus was covered by a piece of opaque tape and the other was left exposed during radiation. PUVA treatment was applied 3 times a week. UVA dose was increased weekly as patients’ tolerance permitted. Patients were asked to avoid sun exposure or any other artificial UV radiation during that period. The mean total UVA dose was 68.86 j/cm² (32.70-98 j/cm²). Table I shows age, sex, skin type, disease, and total dose of UVA during 3 months of study.

Table I. Patient characteristics

The nevi were documented under standardized conditions by both constant illumination and magnification by means of a Dermaphot apparatus (Heine, Optotechnik, Herrsching, Germany) both at the beginning and at the end of 3 months of PUVA therapy. Color dermoscopic images taken before and after PUVA therapy were evaluated by two different observers. All nevi were evaluated according to their size, color and structural features.
The nevus size was evaluated by milimetric measuring of the two largest diameters of the nevus. The color of the nevus was evaluated by the number of color tones of each nevus before therapy. Diagnostic features in surface microscopy proposed in the Consensus Meeting held in Hamburg in 1989 were considered in evaluation of the structural features of the nevi in our study [11]. In spite of the presence of some diagnostic features of acquired melanocytic nevi such as pigment network, brown globules, black dots in all of the examined nevi, melanoma related diagnostic features such as pseudopods, radial streaming, milky way and gray-blue areas were not observed in any of them.
We gave score one (1) when any one feature of a radiated nevus was same as before therapy, score two (2) when there was an enlargement in one diameter, score three (3) when there was an enlargement in two diameters, score two (2) when there was a darkening of color, score three (3) when there was a new color formation, score two (2) when there was a change in one of the structural features, score three (3) when there was a change in two of the structural features.
During PUVA therapy, 14 protected nevi were grouped as group 1 and 14 unprotected nevi as group 2. In order to understand whether all nevi (protected in group 1 and unprotected in group 2) showed significant changes within their own groups before and after therapy, Wil-Coxon test was applied. To compare the changes between group 1 and 2 before and after PUVA therapy, Fisher’s exact probability test was applied.

Results

After PUVA therapy, an increase in size was observed in 6 of 14 protected nevi. Enlargement was detected in both diameters in two nevi and in one diameter in four nevi of 14 protected nevi. This result was statistically significant (p:0.023; p < 0.05). After PUVA therapy, an increase in size was observed in 11 of 14 unprotected nevi. Enlargement was documented in both diameters in four and in one diameter in seven of 14 unprotected nevi. This result was statistically significant (p:0.002; p < 0.01). Enlargement in any diameter in both groups nevi was between 0.3-0.5 mm. Comparing enlargement changes in group 1 and group 2, it was not found to be significant (p:0.20).
Before PUVA therapy, all nevi had two color tones of light brown and dark brown. After PUVA therapy, a general color darkening was seen in brown tones presenting in 9 of 14 unprotected nevi and 8 of 14 UVA protected nevi (Fig. 1A and 1B). No new color formation was detected in either group. Separate statistical evaluation in each group showed a highly significant color change before and after the radiation (p < 0.01). There was no significant statistical difference in color change between group 1 and 2 (p:0.50).
While a mild change in only one structural feature was documented in two protected nevi (prominency in pigment network in one nevus and increase in size of brown globules in the other one), there was no structural change in the remaining 12 protected nevi after therapy. In protected nevi, there was no statistically significant structural change after therapy (p:0.15, p > 0.05). In the unprotected nevi group, there was a change in one or two structural features (these changes: broadness of pigment network, formation of focal branched streaks, increase in number and size of brown globules) in 7 nevi (Fig. 2A and 2B) (Fig. 3A and 3B). In the unprotected nevi, there was a significant structural change (p:0.015-p < 0.05) after PUVA therapy.

Discussion

PUVA therapy is associated with the development of large, irregular, unevenly pigmented macules called PUVA lentigines.These irregular pigmented macules were shown to be developed permanently after ceasing of the therapy in most patients treated with PUVA.
Histologically, there is a proliferation of melanocytes, many of which are large, clustered, binucleate and atypical [12]. The melanocytes of PUVA lentigines often have many long dendrites and show cellular pleomorphism, nuclear hyperchromatism, and angular nuclei. Ultrastructurally, there is an increase in the number and size of the melanosomes and an increase in DOPA reactivity. These PUVA induced atypical changes have been thought to be melanocytic dysplasia or precursors of melanocytic malignancies [13, 14].
It has been shown that PUVA can induce melanocytic tumors in rats and enlargement of melanoma cells in vivo [15]. Although there are animal studies [16, 17] in which UVA exposure has been shown to induce melanoma induction or its progress, results regarding UVA-melanoma/PUVA- melanoma relations in humans are debatable.
The mutagenic (carcinogenic) effect of UV radiation (UVR) is mainly focused on tumor induction by direct DNA damage. The absorbtion of UVR by DNA results in the formation of characteristic dipyrimidine lesions in human epidermis (keratinocytes and melanocytes) in situ. Unless repaired, the molecular rearrangement of adjacent pyrimidine bases may give rise to UVR signature mutations [1]. The immunosuppressive effect of UV radiation also contributes to its carcinogenic activity. It is well established that UVR exposure suppresses cutaneous cell mediated immunity in humans. The depletion of Langerhans cells and release of inflammatory cytokines are important events in the initiation of immunosuppression. UVR-induced immunosuppression plays an important role in the emergence and growth of nonmelanoma skin cancers in mice and a similar role is suspected in humans, because transplant patients maintained on immunosuppressive therapy have an elevated risk of both nonmelanoma and melanoma skin cancer, especially if they also have a history of high sun exposure [1]. Most tumor promoters are known to stimulate cell division. By stimulating melanocyte proliferation, UVR also might act as a tumor promoter [18].
The melanocyte proliferative effect of UV radiation has been the source of investigations of the effects of UV on nevi. Pullmann et al. noted enlargement and color darkening in nevi of the psoriatic patients who had received PUVA and SUP. Proliferation was noted in melanocytes, keratinocytes and dermal lymphohistiocytic cells in histopathologic studies of excised nevi after therapy [6]. Likewise, Larsen et al. showed that mitosis and inflammatory infiltration in histopathological studies of nevi were more marked in summer months than in winter months [7]. Pawlowski et al. in an ultrastructural investigation had found high amounts of centrioles indicating mitotic activity and increased melanin content in nevus cells and keratinocytes in exposed nevi [8]. In a morphologic and immunohistochemical study, the short-term effects of UV light on melanocytic nevi were studied by Tronnier et al. One side of each nevus was exposed and the other side protected. After irradiation, more melanocytes above the dermal-epidermal junction were observed in seven nevi. Moreover, an increase in the expression of HMB-45 was found after irradiation in all investigated nevi, indicating an activation of the melanocytes and active melanosome formation [9].
Studies on rats have shown an increase in the number of melanocytes due to UV effect in both protected and unprotected skin. This event has been interpreted by a systemic mitogenic factor secreted in unprotected skin and by an initiation of melanocyte increase in protected skin [19]. For the first time, Stierner et al. showed that melanocyte increase could be due to UV stimulation of both protected and unprotected skin in humans. Because of stimulation of the cell mitosis (proliferative effect), UV may have a tumor promoting effect both in protected and unprotected skin. This suggested a possible role for the development of melanoma in protected skin. That is, in exposed skin, UV light has both a direct mutagenic and tumor promoting effect, whereas, in covered skin, it may have a tumor promoting effect only [18].
In recent years, several dermoscopic studies have been done on the effects of UV on nevi. Stanganelli et al. found a higher frequency of broad pigment network and black dots in summer than in winter in dermoscopic images of acquired melanocytic nevi [20]. Hofmann-Wellenhof et al. studied nevi of patients receiving suberythemal UVB both before and after therapy and found an increase in total irregularity, and width of pigment network and an increase in brown globules in both protected and unprotected nevi after therapy [21]. Stanganelli et al. found both UV-induced possible changes such as increased thickness and pigmentation of the pigment network, increase in the black dots and atypical images such as radial streaming, pseudopod and blue grey areas in dermoscopic images of nevi which were photographed 5-13 days after sun exposure. However these images disappeared after 5-6 weeks [22]. In another study on 15 melanocytic nevi after a combination of 2 minimal erythema doses of UV radiation by Hofmann-Wellenhof et al., the nevi were found to have a darker brown color and an increase in the number and density of brown-black globules [23].
In present study, we documented darkening of color, increase in size, prominency in pigment network, broadness of pigment network, formation of focal branched streaks and increase in number and size of brown globules in unprotected nevi after therapy. Considering the histopathologic correlates of structures seen on dermoscopy [11] both in our study and in other dermoscopic studies, we suggest that PUVA can induce melanocytic activation. On the other hand, we documented darkening of the color and increase in size in the protected nevi after therapy. In spite of enlarging of the pigmented area and darkening of color in the protected nevi, no significant change was detected in structural elements. These findings make us to think that there may be less melanocyte proliferation in the protected area than the unprotected area. Our findings are in accordance with those of Tronnier et al. [9], Stierner et al. [18] and Stanganelli et al. [21]. Tronnier et al. [9] noted higher numbers of melanocytes seen in the unprotected site of the nevus. Stierner et al. [18] found the fact that the increasing melanocyte numbers in the protected skin were 30% of that of the unprotected skin. Stierner et al. [18] put forward the idea that a mitosis stimulating factor derived from proliferated melanocytes in unprotected skin could stimulate melanocytes of the protected area through a paracrine process and this could explain the delayed response theory in protected skin.
In conclusion, as has been noted in previous studies with sunlight or UVB, it may be suggested that similar changes, caused by possible melanocytic activation and detected by dermoscopy in both protected and unprotected nevi, may be stimulated by PUVA.
To the best of our knowledge, this is the first study investigating the dermoscopic changes caused by PUVA treatment in melanocytic nevi. Further studies with large series are needed. n

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