Progressive macular hypomelanosis
PMH is characterized by numerous hypopigmented macules and patches that affect primarily the lumbar region and abdomen. Rarely, the condition extends to proximal limbs and the neck. While classically absent from the face, rare facial lesions have been described. The hypopigmented macules are ill-defined, nummular, symmetric, and without scale. The lesions are asymptomatic without history of preceding infection, inflammation, or injury.
PMH may last for years, but typically it resolves before age 40. The condition chiefly affects adolescents and young adults, particularly women aged 13-38 years. PMH affects all populations worldwide, but it is more common in tropical regions and in patients with darker skin colors.
The pathogenesis of PMH is unknown. However, studies have suggested that the hypopigmentation may be due to Cutibacterium acnes (formerly known as Propionibacterium acnes). This bacterium is found in the sebum of the pilosebaceous duct within hypopigmented lesions. The precise mechanism by which C acnes causes hypopigmentation is unclear, but it is hypothesized that the organism produces a substance that interferes with melanogenesis and/or melanosome distribution. More recent studies suggest that C acnes subspecies elongatum (type III) may more specifically be associated with PMH, as PMH rarely affects the face and C acnes type III rarely colonizes the face.
L81.9 – Disorder of pigmentation, unspecified
37257004 – Decreased melanin pigmentation
Differential Diagnosis & Pitfalls
- Pityriasis (tinea) versicolor – Scaly hypo- or hyperpigmented macules and patches with fungal elements seen on KOH.
- Pityriasis alba – Hypopigmentation frequently located on the face with fine pityriasiform scaling.
- Postinflammatory hypopigmentation – Presents in a patient with a history of preceding dermatitis or other inflammatory dermatoses.
- Idiopathic guttate hypomelanosis – Confetti-like macules on the extremities, particularly the forearms, calves, and shins.
- Vitiligo – Sharply depigmented macules and patches commonly involving the face, genitalia, and extensor skin, or areas of trauma.
- Sarcoidosis – Red-brown plaques with peripheral elevation and central hypopigmentation.
- Tuberculoid leprosy – Anesthetic hypopigmented macules and patches that are most prominent on the face and extremities.
- Lepromatous leprosy – Can present with many widespread hypopigmented or slightly erythematous lesions. Lesions tend to be more prominent on the cooler parts of the body (eg, nose, earlobes, eyebrows, cheeks, ears, buttocks, and extensor and acral extremities).
- Cutaneous leishmaniasis lesions – May heal without therapy, leaving a hypopigmented, atrophic scar. Active lesions usually develop central ulceration. Microscopy or biopsy often reveals the presence of parasites.
- Secondary syphilis – A papulosquamous eruption involving the trunk and extremities, including the palms and soles. History of primary chancre should raise concern for this diagnosis, and most patients present with systemic symptoms such as fever, headache, sore throat, and malaise.
- Incontinentia pigmenti – Evolves from birth through childhood with hypopigmentation being the fourth (last) stage in the progression. Stages 1-3 represent a vesicular stage, verrucous stage, and hyperpigmented stage, respectively.
- Arsenic hypomelanosis (arsenical keratosis) – Hyperpigmented macules and "raindrop" hypomelanosis. A history of chronic arsenic exposure should be noted.
- Hypopigmented mycosis fungoides – Hypopigmented scaly patches and plaques commonly located on the trunk, pelvic girdle, and lower limbs. Lesions are also associated with pruritus, poikiloderma, and ulceration.