Comment
Etiology
Acrokeratoelastoidosis was first described in 1953 and is considered a type of palmoplantar marginal papular keratoderma.1 There is overlap within the marginal papular keratodermas that makes precise diagnosis difficult within this group. The marginal papular keratodermas on the palms and soles are a group of disorders that include AKE, focal acral hyperkeratosis (FAH), mosaic acral keratosis, degenerative collagenous plaques on the hands, and digital papular calcific elastosis. These diseases are similar in clinical and histopathological features; some argue these diseases are the same entity.2
Acrokeratoelastoidosis has been hypothesized to originate from altered elastic fiber synthesis from fibroblasts.3 Because AKE is rare, most cases of common knuckle pads do not coexist with AKE; therefore, it is unknown if the underlying etiology remains the same for both entities. Unlike AKE, knuckle pads are often associated with Dupuytren contractures, repetitive trauma, or friction to the area.1,2
Presentation
Acrokeratoelastoidosis is a rare disease with onset in childhood or young adulthood. Childhood cases are inherited in an autosomal-dominant fashion.1 Adulthood onset suggests a sporadic form of inheritance. Acrokeratoelastoidosis has no gender or racial predilection.4 It presents over the thenar and hypothenar eminences, as well as the lateral digits, calcaneal tendon, and dorsal digits.1 Most often, AKE occurs symmetrically along the border separating the ventral and dorsal aspects on the palms and soles. These lesions present as small, firm, translucent papules that align linearly on the ventral-dorsal palmoplantar junction in a pattern resembling paving stones.1 Coalescence of papules into plaques has been reported. Extension of lesions to the dorsal and palmar surfaces can occur. Small circumscribed callosities may develop over the metacarpophalangeal and interphalangeal joints resembling knuckle pads.2
Histopathology
Histopathologically, AKE is distinguished by elastorrhexis—thinning, fragmenting, and rarefaction of elastin fibers—in the epidermis and reticular dermis layers.3 Acrokeratoelastoidosis also presents with orthokeratosis overlying a cuplike epithelial depression and possible epithelial acanthosis.2,5 Many cases exhibit hypergranulosis at the base of the epidermal dell. Dense basophilic granules may be seen in the peripheral cytoplasm of fibroblast cells coming from the hypothesized defect in elastin secretion.1,3,4
Differential Diagnosis
The main differential diagnosis of AKE is FAH. Clinically and histopathologically they appear identical; both diseases have cuplike epidermal depressions with overlying orthohyperkeratosis and prominent hypergranulosis.5 The elastin stains, Verhoeff-van Gieson or acid orcein stain, are imperative for distinguishing these two diseases. Although AKE demonstrates elastorrhexis and reduced elastic fibers, FAH reveals no alteration of elastic fibers. It has been suggested that FAH is a clinical variant of AKE and should be titled AKE without elastorrhexis.1
Treatment
Acrokeratoelastoidosis is asymptomatic except for mild palmoplantar hyperhidrosis and typically does not require treatment4; however, the condition can be of cosmetic concern for patients. Lesions can be treated topically with keratolytics such as tretinoin and salicylic acid. A wide variety of systemic treatments including methotrexate, prednisolone, dapsone, and acitretin have been reported with variable clinical response.2-4 Copresenting knuckle pads can be treated with urea cream, salicylic acid cream, or intralesional corticosteroids.1