The lesions were round-to-oval, ill-defined, hypopigmented, non-scaly, 1- to 3-cm confluent macules and patches confined to the lower back (Figure). A potassium hydroxide(Drug information on potassium hydroxide) (KOH) examination was negative for fungal elements, and the patient showed no signs or symptoms of atopic dermatitis. The clinical picture was consistent with a diagnosis of progressive macular hypomelanosis (PMH) of the trunk. Treatment was initiated with topical benzoyl peroxide(Drug information on benzoyl peroxide) and clindamycin(Drug information on clindamycin), and the lesions gradually resolved over several weeks.
Discussion
PMH of the trunk was first described by Guillet et al1 in patients of mixed ethnicity, (eg, French-Caribbean). Currently it is more prevalent in multiethnic communities where genetic backgrounds are mixed which presents in skin types IV-VI. The condition usually manifests in young adults, particularly women, in their 20s and 30s. PMH of the trunk is found throughout the world and has been variously referred to as cutis trunci variata, creole dyschromia,2,3 nummular and confluent hypomelanosis of the trunk, and idiopathic multiple large-macule hypomelanosis.4
PMH is often confused with tinea versicolor and pityriasis alba, both of which also present with multiple oval-to-round hypopigmented confluent macules and papules on the trunk. The rapid spread of PMH also may lead to confusion with other diseases, and is frequently a cause of concern for patients and family members.
Unlike tinea versicolor, PMH lesions lack surface scale and do not show hyphae or spores on KOH examination, on histologic examination with hematoxylin and eosin staining, or with Periodic-Acid-Schiff stain. To differentiate pityriasis alba from PMH, look for subtle scale as well as other atopy stigmata that may accompany pityriasis alba. Additionally, some studies have demonstrated that under Wood’s light a red follicular fluorescence caused by the presence of Propionibacterium acnes may sometimes be visualized in the PMH lesions.5 It has been hypothesized6 that the pathophysiology of PMH involves a shift from large melanosomes in normal-appearing skin to small, aggregated, membrane-bound melanosomes in hypopigmented skin.
PMH should also be differentiated from:
• Tuberculoid leprosy—almost always presents with loss of sensation, not a feature of PMH
• Cutaneous T-cell lymphoma (mycosis fungoides)—borders are typically well defined, more common in the extremities, may be pruritic
• Post-inflammatory hypopigmentation—history of previous lesions, localized to those areas
Management. Treatment for PMH of the trunk is often ineffective. Most cases resolve spontaneously within 3-5 years. Phototherapy or extensive sun exposure can make the white spots less apparent. A recent study demonstrated that 6 patients treated with narrow band ultra-violet B UVB (311 nm) administered 2-3 times weekly showed some improvement.7 To date, the most promising regimen is 1% clindamycin lotion applied during the day, 5% benzoyl peroxide gel at night, and UVA phototherapy 3 times weekly for 12 weeks.8
PMH is a frequently under-recognized condition that is often confused with other similar-appearing skin disorders, such as tinea versicolor and pityriasis alba. It is important to correctly identify these conditions to provide appropriate treatments and improve outcomes.
Teaching Points
• In patients with non-scaly ill-defined hypopigmented macules that have failed previous treatments for TV or other conditions, consider a diagnosisi of PMH
• Most treatment for PMH is ineffective but some promising results have been seen with clindamycin 1% applied during the day and 5% benzoyl peroxide gel at night, with phototherapy 3 times weekly for 12 weeks.
