Progressive macular hypomelanosis (PMH) is a reaction to the bacteria P. acnes that results in white patches on the trunk. These lesions show red fluorescence in a follicular pattern which is helpful in diagnosis. In the laboratory, Propionibacterium acnes may be cultured from the follicles. It is thought that the P. acnes secretes a factor that interferes with melanogenesis.
The patchy hypopigmentation of PMH is often misdiagnoses as tinea versicolor, but lacks erythema and scale and is resistant to antifungal treatment.
Hypopigmented areas are seen on the trunk, often lower trunk in a young person. Wood's light shows follicular flourescence, so called "starry sky".
Oral antibiotics that target P. acnes should be give, e.g. doxycycline or minocycline 100 mg BID for 3 months. Topical benzoyl peroxide may also be recommended. Exposure to the sun during therapy may hasten resolution. Other treatments include isotretinoin [J Dermatol. 2012;39:937-8], nbUVB, and a combination of 5% benzoyl peroxide and 1% clindamycin. One study of 13 patients used 300 mg of lymecycline daily, 5% benzoyl peroxide at night and 3/week exposure to the sun for 12 weeks with excellent results [An. Bras. Dermatol. 2011;86].
One study of UVB found that 90% of patients achieving greater than 80% repigmentation[Indian J Dermatol Venereol Leprol 2016;82:673-6]. The time for the first response was usually within 4–8 sessions of narrow-band ultraviolet B and time for maximal repigmentation was about 22 sessions. If patients do not respond within 12 sessions, it may not be advisable to continue with phototherapy.
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