A 72-year-old male presents for evaluation of slightly tender and annoying growths that have appeared over the last year on his palms and soles. The patient is otherwise healthy. He grew up on a farm in central Missouri and is now retired after years of manual labor.
This patient has changes consistent with arsenical keratosis. This condition is a rare occurrence in this country, which is attributed to elevated arsenic levels in the drinking water, especially in areas that rely on well water and with a history of using arsenical based pesticides. Of interest, arsenical based pesticides were used by tobacco farmers for years, which resulted in marked increase in arsenic levels in tobacco, tobacco smoke, and the ground water.
Studies suggest that only 10% to 30% of individuals are susceptible to developing arsenical keratosis after several years of chronic exposure. The clinical clue to the diagnosis is found in the lesions, which are most frequently seen on the thenar and lateral borders of the palms; the base and lateral aspect of the digits; and the soles, heels, and toes of the feet.
A dose-response relationship exists between the amount of arsenic exposure and the frequency of various skin lesions. Several studies have shown skin lesions that have developed in persons who consumed drinking water containing arsenic concentrations of less than 50 µg/L. A review of the US Geological Survey map shows a high risk area in central Missouri. Other sources of arsenic include treated lumber and traditional Chinese herbal medicines.
Differential Diagnoses: Warts are less likely given the sudden onset, symmetrical distribution and appearance. Palmoplantar keratoderma is a consideration though it is typically early onset or appears around age 20. Clavus or corns are typically confined to the feet at pressure points. Epidermodysplasia verruciformis is a rare autosomal recessive condition that typically presents in early childhood with human papillomavirus lesions on the dorsum of the hands, but tends to spread widely beyond the distal extremities.References:
1. Satterlee HS. The problem of arsenic in American cigarette tobacco. N Engl J Med. 1956; 254:1149-1154.
2. Ryker SJ. Mapping arsenic in groundwater. Geotimes. 2001;46(11):34-36.