Progressive macular hypomelanosis

Progressive macular hypomelanosis is an uncommon skin condition characterised by ill-defined, circular, non-scaly, hypopigmented macules on the trunk, often confluent in and around the midline, and rarely extending to the proximal extremities and neck/head region.

This chapter is set out as follows:

• There is a theory that Cutibacterium acnes (C. acnes - formerly known as P. acnes) bacteria living in hair follicles are the cause of progressive macular hypomelanosis (PMH) as a result of the production of a hypothetical depigmenting factor

• PMH mainly affects teenagers and adults and is most common in young women 
• It is more common in skin of colour  

Distribution

• ​PMH mainly affects the trunk, rarely extending to the proximal limbs and/or head and neck

Morphology

• Characterised by ill-defined macules
• Lesions often become confluent, in and around the midline, to form patches 
• Unlike pityriasis versicolor, lesions are not scaly, and unlike post-inflammatory hypopigmentation (eg secondary to eczema or psoriasis), there is no preceding inflammation 
• On Wood's light examination the hair follicles fluoresce with a red glow, indicating they are colonised by P. acnes

• The clinical course of PMH is unpredictable, but spontaneous resolution can occur within years or decades

• The condition is generally unresponsive to treatment, including topical acne treatments such as clindamycin and benzoyl peroxide, oral tetracyclines, and phototherapy