Progressive macular hypomelanosis (PMH) of the trunk was first described in 1988 by Guillet et al.1. Previous reports have referred to this condition as cutis trunci variata2, dyschromia creole3, or idiopathic multiple large macule hypomelanosis4. PMH is characterized by non-scaly, hypopigmented macules on the trunk and upper extremities, with no history of skin disease. The histologic findings include decreased numbers of epidermal melanin granules in hypopigmented lesions compared with normal skin1. Current treatments for PMH include topical and systemic antifungal agents, topical steroids, and psoralen with ultraviolet A light (PUVA). However, no consistently effective therapy is known. Cases of PMH in Koreans have been reported in the literature5,6, but no clinicopathologic studies of PMH in Korean patients have been published. The purpose of the current study was to document the clinical, pathologic, and histologic properties and treatment methods for 20 Korean patients who were diagnosed with PMH over a 10-year period.

Guillet et al.1 reported hypopigmented macules on the trunk in patients of mixed ethnic origin (black/white) in 19851. Guillet et al.1 later coined the term PMH of the trunk in 1988. PMH is an idiopathic skin disorder characterized by hypopigmented macules predominantly located on the trunk without scales or a history of skin problems. PMH is more common in tropical and subtropical regions than in other geographic areas. In Korea, there have been only three published case reports of PMH, and there have been no studies pertaining to the prevalence of PMH5,6. In the present study, we excluded all patients who declined a skin biopsy, even if they showed typical symptoms of PMH. Although we do not know the exact prevalence of PMH, it is likely that PMH is not a rare disease in Korea. Moreover, PMH may be more common in young women. The proportion of males-tofemales in this study was 1:3, and the mean age of onset was 21.05±3.47 years, which is compatible with the predominance of PMH in young female patients. However, women are known to access the healthcare system more than men, especially their cosmetic problems, therefore, the frequency measurements in men and women may have some limitations.

Clinically, PMH is characterized by ill-defined, non-scaly, round-to-oval, asymptomatic, and symmetric hypopigmented macules. Indeed, the lesions may become confluent, forming large hypopigmented macules after an increase in their number1. The patients in our study presented with the clinical characteristics described by Guillet et al.1. The histopathologic findings in PMH are usually non-specific, but one common feature is that the melanin content in the lesions is lower than that in normal skin7. The ultrastructural findings in PMH include decreased epidermal levels of melanin and fewer melanized melanosomes in the lesional skin8. Choi and Hann5 reported a mild perivascular inflammatory cell infiltration and dermal melanophages, and Westerhof et al.9 reported gram-positive bacteria in pilosebaceous units. The number of melanin granules in the skin lesions of our patients appeared to be lower than in the adjacent normal skin, but no other findings were observed (Fig. 3).

Immunohistochemical staining with anti-S-100 antibodies revealed no significant difference in the number of melanocytes between the hypopigmented lesions and normal skin (Table 2, Fig. 4).

The etiology of this condition is uncertain, but many hypotheses have been proposed. Guillet et al.1 suggested that ethnicity is an important factor, and Borelli2 classified PMH as a genetic dermatosis. However, none of the 20 patients we examined had a family history of PMH, and we could not find any genetic influence. Sober and Fitzpatrick4 proposed a relationship with tinea versicolor, but that was excluded in our study. Moreover, there was no development of Malassezia furfur in the PMH lesions. Using a Wood's lamp, Westerhof et al.9 observed a follicular pattern of red fluorescence inside the lesional skin of patients with PMH, and Propionibacterium acnes was isolated from biopsies of lesional follicular skin in all patients except one. It was concluded that P. acnes, which is detected in pilosebaceous units, produces a factor that interferes with melanogenesis. Thus, P. acnes is a suggested etiologic factor in PMH. Many of the patients in our study were enrolled before 2004, when P. acnes was proposed as a cause of PMH; therefore, a Wood's lamp examination for the observation of a follicular pattern of red fluorescence was not performed. Hypopigmented lesions usually develop at sites that are not exposed to sunlight, and NBUVB phototherapy improves the skin lesions in patients with PMH. Therefore, we propose that epidermal melanin synthesis is temporarily decreased or stopped by reduced sunlight exposure, leading to the appearance of hypopigmented macules.

There are many follow-up reports of PMH. Guillet et al.1 suggested that hypopigmented lesions spontaneously decrease after 2~5 years. In the present study, we followed 3 patients who did not receive treatment for 3 months to 8.33 years. Only one of those patients improved, with a time-to-repigmentation of 8.33 years (Table 3). More extensive follow-up is needed to confirm the spontaneous resolution of PMH.

Topical and systemic antifungal agents, topical steroids, topical antimicrobial agents, and PUVA therapy have been used to treat PMH; however, no consistently effective therapy has been established. Relyveld et al.10 compared the effectiveness of antimicrobial therapy (5% benzoyl peroxide hydrogel/1% clindamycin lotion) with anti-inflammatory therapy (0.05% fluticasone cream) in patients with PMH. Relyveld et al.10 concluded that antimicrobial therapy with light was a more effective treatment modality, which supports the hypothesis of Westerhof et al.9 that P. acnes is causally related to PMH. Kim et al.6 reported that one Korean patient improved after NBUVB phototherapy. Although topical antimicrobial therapy was not used in that study, one of our patients improved after taking an antimicrobial agent (minocycline hydrochloride; Table 3). However, this patient stopped treatment on his own volition after taking oral minocycline for only 1 month, and repigmentation developed after 1 year. Similarly, the one patient who showed repigmentation after treatment with a topical drug had stopped using 1% hydrocortisone lotion after only 4 months, and repigmentation developed after 40 months. Therefore, it is difficult to conclude if a successful outcome was achieved with minocycline hydrochloride or topical steroid application. In contrast, six patients treated with NBUVB phototherapy showed marked repigmentation, and hypopigmented lesions did not recur during 3~13 months of follow-up. Therefore, we suggest that NBUVB phototherapy is an effective treatment for PMH. In a previous study, NBUVB phototherapy was shown to promote melanocyte proliferation and migration and to diminish the activation of interleukin-6 and tumor necrosis factor-α, which suppress melanin synthesis11,12. This resulted in repigmentation of the hypopigmented lesions.

In conclusion, patients presenting with acquired, non-scaly, confluent, hypopigmented macules on the trunk should be evaluated using KOH mounts, Wood's lamp examination, or skin biopsies to rule out other hypopigmented diseases. Moreover, a special diagnosis of PMH should be considered. In Korean PMH patients, the most frequently affected sites were the back and abdomen, with a reduced occurrence on the buttocks and chest. Histologically, the number of S-100-positive melanocytes did not differ significantly between the hypopigmented macules and normal perilesional skin. No effective treatment is known for PMH; however, NBUVB phototherapy may be useful. This is the first clinicopathologic study of PMH in Koreans. Additional studies with greater numbers of patients are necessary to certify the clinical characteristics, histologic findings, and therapeutic outcomes of PMH in Koreans.