Lichen planus pigmentosus (LPP)

Lichen Planus Pigmentosus (LPP) is a subtype of lichen planus that predominantly affects individuals with skin phototypes III-V,^[4] commonly appearing in the third to fourth decades of life. Characterized by chronicity with periods of exacerbation and remission, LPP has various identified causes, including an unknown antigen triggering a lichenoid inflammatory reaction, UV irradiation, mustard oil (containing a potential photosensitizer - allyl thiocynate), and amla oil (mainly in Indian skin). Clinically, patients exhibit oval or round macular hyperpigmentation in sun-exposed areas such as the forehead, temples, and neck, ranging from slate grey to brownish black, presenting in diffuse, reticular, blotchy, and perifollicular forms. LPP can also manifest in skin folds like axillae and groin (LPP inversus). Although typically asymptomatic, there is a rare unilateral linear variant following blaschko’s lines. Dermoscopic features include dots and globules, exaggerated pseudo-reticular pattern and peri-follicular pigmentation.^[5], ^[6] Histopathological examination reveals basal layer vacuolation with epidermal atrophy, melanophages in the superficial dermis and perivascular lymphocytic infiltrate.^[7] Differential diagnosis include lichen planus ( actinic, inverse variant), erythema dyschromicum perstans, post inflammatory hyperpigmentation, lichenoid drug eruption. Treatment options such as photoprotection, topical tacrolimus 0.1%, topical and systemic corticosteroids, topical vitamin D have been tried with variable success.

Vitamin B12 deficiency associated pigmentation

Vitamin B12 (cobalamin) is a water soluble B complex vitamin. ^[8] It is obtained through dietary sources such as eggs, milk, beef, liver and organ meats. It is a critical co-enzyme involved in DNA, proteins, lipid and carbohydrate metabolism. ^[8] Deficiency may arise due to intrinsic factor deficiency, achlorhydria, ileac disease, malnutrition, malabsorption syndromes, or a strict vegetarian diet. ^[9] The patients present with anemia, neurological manifestations such as loss of vibration, proprioception, spasticity, paraplegia, urinary incontinence, mucocutaneous features such as glossitis, angular cheilitis, localised or diffuse hair depigmentation and cutaneous hyperpigmentation of face, nails, acral pigmentation involving hands and feet, palmar creases and flexural surfaces. ^[8], ^[10] The pathogenesis of cutaneous hyperpigmentation due to vitamin B12 deficiency is poorly understood. Decreased vitamin B12 causes decrease in glutathione levels which leads to decrease in inhibitory effect on tyrosinase enzyme, thus leading to increased melanogenesis. ^[10] Vitamin B12 deficiency also causes defective melanin transfer from melanocytes to adjacent keratinocytes. ^[8] Blood tests reveal macrocytic anemia, hyper-segmented neutrophils and reduced serum vitamin B12. ^[9] Histopathology shows hyperkeratosis, increased melanin granules in the basal layer, scattered melanophages, and

perivascular lymphocytic infiltrates in the upper dermis.Histopathology shows hyperkeratosis, increased number in melanin granules of the basal layer, scattered melanophages along with perivascular lymphocytic infiltrates in upper dermis.^[11] Treating the underlying cause reverses the hyperpigmentation. Conditions such as pernicious anemia, impaired absorption require parenteral vitamin B12 administration. In other cases, oral supplementation of 1-2 mg daily in the initial months, followed by gradual tapering, is recommended. ^[8]

Dyschromatosis symmetrica hereditaria

Dyschromatosis symmetrica hereditaria, also known as reticulate acropigmentation of Dohi (RAD), is a rare autosomal dominant inherited disorder caused by a mutation in the double-stranded RNA-specific adenosine deaminase gene. This gene encodes an RNA editing enzyme. Patients with RAD develop progressive hyperpigmented and depigmented macules, typically in a reticulate pattern, primarily on the dorsal extremities. Freckle-like macules are also present on the face, with onset in infancy or early childhood and a tendency to increase in size until adolescence. Hyperpigmented lesions exhibit increased melanin pigment at the basal layer, while hypopigmented lesions show decreased or absent melanin pigment. Differential diagnosis includes reticulate acro-pigmentation of Kitamura (RAPK), characterized by hyperpigmented, atrophic, angulated macules primarily on the hands, gradually extending over the extremities, and rarely involving the face. Breaks in the epidermal ridge pattern and palmar pits are characteristic of RAPK. ^[12], ^[13], ^[14], ^[15], ^[16] Although there is no effective treatment for these conditions, various agents including topical retinoids, azelaic acid and Er:Yag laser have been successfully tried. ^[17]

Talon noir

Talon noir is a condition marked by painless petechial lesions, commonly found in acral body sites. Its distinct presentation involves merging macules forming a blackened purpuric plaque, leading to its naming by French dermatologist Peachey. The pathogenesis is attributed to shearing forces in activities such as sports or climbing, causing damage to papillary dermal blood vessels and blood seepage to the epidermis.Talon noir is a condition that presents with asymptomatic petechial lesions, trauma-related and mostly found in acral body sites.^[18] The most typical appearance of this clinical entity is the presence of coalescing macules forming a blackened purpuric plaque. It was precisely this appearance that gave rise to the denomination of the dermatosis, termed by the French dermatologist Peachey as talon noir, which means black heel.^[19] The aetiology can be explained by damage of the papillary dermal blood vessels due to shearing forces related to sports activity, climbing, or any kind of repetitive microtrauma that eventually leads to the leakage of blood from the dermis to the epidermis.^[20], ^[21] Differential diagnoses usually include acral melanoma, acral nevi, plantar wart, pyogenic granuloma, angiokeratoma, corn, and tinea nigra.^[22], ^[23] Dermoscopy, a non-invasive procedure, can differentiate talon noir from melanoma preoperatively as the former shows homogenous reddish globular structures. ^[24] Acral melanoma, on the contrary, shows a typical parallel ridge pattern with irregular pigmentation. ^[21], ^[25], ^[26] Confirmation of diagnosis can be done by histopathological examination, which shows hyperkeratosis, presence of blood in the stratum corneum and extravasated erythrocytes in the papillary dermis. ^[18] It is a benign condition which usually subsides within few weeks by avoiding sports activity or any kind of repetitive trauma and using well-cushioned shoes, thick socks and lubrication. Exanthema associated capillary fragility can be benefited from vitamin C supplementation. ^[27], ^[28], ^[29]

Acral melanoma

Laugier–Hunziker syndrome (LHS

Laugier–Hunziker syndrome (LHS) is a pigmentary condition involving lips, oral mucosa, and acral areas, commonly linked with longitudinal melanonychia. ^[30] Typically observed in middle-aged adults around 50 years old, it is more prevalent in women, especially among Whites, notably the French and Italians.^[31], ^[32] LHS manifests as asymptomatic brown to black macules, usually less than 5 mm in diameter, over the lips, buccal mucosa, hard palate, and occasionally other oral areas.^[31], ^[32] Nail involvement occurs in 50–60% of cases, presenting as single or double stripes or complete nail pigmentation. ^[31], ^[33], ^[34], ^[35], ^[36], ^[37] Dermoscopic examination reveals linear brown pigmentation and multiple brown dots in regular pattern on mucosal lesions. Histologically, there is hyperpigmentation of basal keratinocytes with melanin-laden macrophages. A key differential diagnosis is Peutz–Jeghers syndrome (PJS). Cosmetic treatments for LHS involve cryosurgery, Q-switched Nd:YAG, and Q-switched alexandrite laser therapy, with sun protection crucial for prevention. ^[38]