One of the long term effects of arsenic poisoning is keratosis, which usually occurs decades after arsenic exposure in drinking water and food. In Europe the diagnosis of arsenic keratosis is not concluded frequently, as exposure is low and only recorded in some wine growing regions which historically used arsenic pesticides. In China though, cases are more common, as heavy metals may cause poisoning of patients using Traditional Chinese Medicine, are exposed at their work place or contaminated drinking water and food. This may be why physicians in Asia diagnose it easier. Arsenic keratosis is hard to treat and even to manage and it may trigger cancers. A very good description of the cell patterns related to arsenic keratosis, you find by clicking here. Some research shows that oral retinoids, like acitretin or its metabolite etretinate (which has been discontinued in some markets because of the high risk of birth defects and complicated dosing due to a long half life of about 120 days), may reduce the risk of cutaneous and internal malignancy formation. I found the following related papers:

Son SB, Song HJ, Son SW. Successful treatment of palmoplantar arsenical keratosis with a combination of keratolytics and low-dose acitretin. Clin Exp Dermatol. Mar 2008;33(2):202-4.
Yerebakan O, Ermis O, Yilmaz E, Basaran E. Treatment of arsenical keratosis and Bowen's disease with acitretin. Int J Dermatol. Feb 2002;41(2):84-7.
Sharma SC, Simpson NB. Treatment of arsenical keratosis with etretinate. Acta Derm Venereol. 1983;63(5):449-52.

Non-oral treatment has been undertaken with imiquimod cream and is described in: Boonchai W. Treatment of precancerous and cancerous lesions of chronic arsenicism with 5% imiquimod cream. Arch Dermatol. Apr 2006;142(4):531-2.

Surgical removal and destruction of cell clusters have been are working if applied properly. Treatment with salicylic acid (for example Duofilm Gel) seem does not reach the cells causing the keratosis over-formation.