Ashy Dermatosis and Lichen Planus Pigmentosus: The Histopathological Differences

Skin of color in dermatopathology: does color matter?

Skin of color (SoC) remains an understudied and under taught area of dermatology despite its rising importance. Race and ethnicity play a particularly important role in dermatology as skin pigmentation can affect the manifestation and presentation of many common dermatoses. With this review, we seek to review pertinent differences in SoC histology, as well as highlight the histopathology of conditions more common in SoC and address inherent bias that may affect accurate dermatopathology sign out.

Extensive acquired macular hyperpigmentation in a teenager

A teenage girl with phototype IV skin presented with extensive gradually progressing asymptomatic macular hyperpigmentation not responding to topical steroids for several months. Histopathology showed foci of increased numbers of melanophages and melanin in the dermis.

Positive Antinuclear Antibody and Blaschkoid Lichen Planus Pigmentosus

Lichen planus pigmentosus is a rare variant of lichen planus. It is an acquired pigmentary disorder of unknown etiology. It is characterized by dark brown and slate gray macules and patches. The nails, scalp, and oral mucosa are usually spared, unlike lichen planus. Lichen planus pigmentosus commonly involves the head and neck region as well as intertriginous areas such as the axillae, inframammary and inguinal regions. It can be associated with autoimmune diseases, endocrinopathies, and other variants of lichen planus such as fibrosing alopecia of the scalp. Variable clinical patterns of lichen planus pigmentosus including zosteriform, linear, and segmental had been published. Histopathologically, it is characterized by hyperkeratosis of the epidermis, hypergranulosis, variable degrees of lichenoid infiltration depending on the age of the lesion, and prominent melanin incontinence. Recent updates on erythema dyschromicum perstans that were considered similar to lichen planus pigmentosus, concluded that they could be differentiated on clinical bases as well as histopathology. Epidermal hyperkeratosis, hypergranulosis, apoptotic cells, lichenoid dermatitis, periappendageal infiltrate, and fibrosis with marked superficial dermal melanin incontinence aid to differentiate lichen planus pigmentosus from erythema dyschromicum perstans. During embryogenesis, cells migrate and follow developmental lines named after Blaschko, a German dermatologist, who first noted them. Blaschko’s lines (BL), do not follow neural, vascular, or lymphatic pathways. They appear as V-shaped on the back, S-shaped on the abdomen, and linearly on limbs. We report a case of lichen planus pigmentosus over BL that is a rare presentation of the disease and associated positive antinuclear antibody (ANA) without overt manifestations of any connective tissue disease.