They often coalesce near the midline, and occasionally extend beyond the trunk to the arms, legs, head, or neck. PMH is more frequently diagnosed among black individuals, although it affects all races and ethnicities. The natural history of PMH can vary from stable and progressive disease, and may resolve spontaneously after a few years. The pathogenesis of PMH remains unknown. It has been proposed that the hypopigmentation is caused by decreased melanin production and altered melanosome dispersal in reaction to Propionibacterium acnes.
PMH must be distinguished from some of its clinical mimickers, including vitiligo, hypopigmented mycosis fungoides, tinea versicolor, and pityriasis alba. Potassium hydroxide preparations can be performed in the office to evaluate for tinea versicolor. An additional tool to aid in diagnosis is the use of a Wood’s light. The lesions of PMH characteristically show punctiform orange-red follicular fluorescence when exposed to a Wood’s light, indicating the presence of a porphyrin-producing organism, presumably P. acnes. A skin biopsy is necessary to rule out hypopigmented mycosis fungoides.
Skin biopsy of PMH typically reveals decreased melanin with a normal number of melanocytes. In our patient, a punch biopsy of the right lateral arm demonstrated minimally decreased density of epidermal melanocytes with dermal pigment incontinence. SOX10 immunohistochemical staining demonstrated scattered melanocytes in the epidermis. Preserved melanin within keratinocytes was noted.
In our patient, there was significant spread to the face, which is highly unusual and has only been documented in a few case series. There are no standard recommendations for definitive treatment of PMH. Topical antimicrobial therapies, such as clindamycin solution and benzoyl peroxide gel, have been beneficial in some studies. Tetracyclines, narrow-band ultraviolet B phototherapy, and even isotretinoin have had some reported success.
This case and photo were submitted by Mr. Franzetti, Dr. Rush, and Dr. Shalin of the University of Arkansas for Medical Sciences, Little Rock.
Donna Bilu Martin, MD, is a board-certified dermatologist in private practice at Premier Dermatology, MD, in Aventura, Fla. More diagnostic cases are available at mdedge.com/dermatology. To submit a case for possible publication, send an email to [email protected].