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The differential diagnosis of punctate keratoses of the palms and soles can be extensive (Table 2).4,11-22 Following is a discussion of the clinical characteristics of the acquired and hereditary forms of primary punctate palmoplantar keratoses.
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Arsenical keratoses are one of several cutaneous manifestations of long-term arsenic exposure. Sources of exposure to this toxic metal include well water, medicine, mining and smelting of various metals, and industrial pollution.11-12 Drinking water contaminated with naturally high levels of inorganic arsenic is a significant problem in many parts of the world. For example, in Bangladesh and West Bengal, India, an estimated 79.9 million and 42.7 million inhabitants, respectively, are exposed to groundwater arsenic concentrations that far exceed the World Health Organization maximum permissible limit of 50 µg/L.12 In both of these populations, the primary source of drinking water is from tube wells, which draw water from underground aquifers contaminated with geological sources of arsenic.12 Arsenical keratosis is characterized by hyperkeratotic papules that typically develop over the palms and soles. The lesions may appear anywhere between 4 to 30 years after exposure and may degenerate into squamous cell carcinoma or, more rarely, basal cell carcinoma.11-13 A detailed history is thus warranted if arsenic exposure is suspected. Associations with internal malignancies, including hepatic angiosarcoma, bronchial adenocarcinoma, bladder cancer, and nonmelanoma skin cancer, have been reported.11-14
Keratosis punctata of the palmar creases appears to be predominantly found in the Afro-Caribbean population, but the prevalence is unclear, varying from 1.5% to 69% in different series.4,15-17 The lesions are characterized by discrete, translucent, keratotic papules primarily in the palmar creases of the hands. They are usually asymptomatic but may be painful. Many authors suggest this disease is related to manual labor. No associations with malignancy have been reported.4,5,15-17
Spiny keratoderma is an autosomal-dominant condition with an age of onset ranging from 12 to 59 years.18-20 Clinical presentation is characterized by numerous tiny keratotic spines over the entire palmoplantar surfaces, resembling the spines of an old-fashioned music box.18 Histologically, these spines correspond to columnar parakeratosis resembling cornoid lamellae. This finding is absent in the KPPP form. The term spiny keratoderma was coined by Osman et al18 to distinguish this condition from porokeratosis, which is clinically and histologically a distinct entity. Confusion exists about whether or not the lesions of spiny keratoderma are a form of porokeratosis because previously designated names incorporated the term porokeratosis. The names punctate porokeratotic keratoderma, porokeratosis punctata palmaris et plantaris, and punctate porokeratosis of the palms and soles have been previously used to describe these spiny lesions.18-20 The punctate variant of true porokeratosis is clinically characterized by discrete 1- to 2-mm seedlike hyperkeratotic plugs surrounded by a thin raised margin.21-22 These lesions may be arranged linearly or may coalesce to form plaques, which are not observed with spiny keratoderma.21 The histologic hallmark of porokeratosis is the cornoid lamella, which consists of a thin column of parakeratotic cells extending through the surrounding orthokeratotic stratum corneum, an absent granular layer below the column of parakeratosis, and vacuolated or dyskeratotic cells at the base. Proper classification is needed because malignant degeneration has been reported with certain variants of porokeratosis.18,21
Acrokeratoelastoidosis and focal acral hyperkeratosis are clinically similar entities and share an autosomal-dominant inheritance pattern. Clinical findings consist of 2- to 4-mm round to oval keratotic papules on the borders of the hands, feet, and wrists. The papules may be umbilicated in some cases and may become confluent in the center of the palms and soles. The lesions typically first develop in childhood or adolescence but may occur in adult life. Local hyperhidrosis may be present in acrokeratoelastoidosis but has not been reported for focal acral hyperkeratosis. These 2 entities are mainly distinguished histologically. Focal acral hyperkeratosis exhibits only hyperkeratosis, whereas acrokeratoelastoidosis has the additional finding of elastorrhexis. There have been no reported associations with malignancies.3,23
Keratotic palmoplantar papules also are cutaneous manifestations of multisystem disorders such as Darier disease and Cowden disease.24-25 Patients with these disorders typically have a multitude of other mucocutaneous and systemic findings to support these diagnoses. Histologically, the keratotic lesions of Darier disease are similar to that of KPPP in that hyperkeratosis is found in both. However, Darier disease also demonstrates follicular plugging, parakeratosis, and irregular acanthosis with papillomatosis.24 The keratotic lesions of Cowden disease show nonspecific orthokeratosis, hypergranulosis, and acanthosis.25 A thorough examination, family history, and histologic evaluation are all necessary to make an accurate diagnosis.