Sources differ regarding the average age of onset for KPPP; some report onset from infancy to 70 years.5-7 For KPPC, the age of onset generally is between 15 and 40 years.3 Among African Americans, the prevalence of KPPC is between 1.9% and 3.1%,3,6,8 whereas the prevalence of KPPP may be up to 11%.3,4 While KPPP is largely asymptomatic, the lesions of KPPC tend to be noticed more often. Once present, KPPP lesions usually remain stable over time, whereas, KPPC lesions usually increase in number and size.3
Demographics and causes
KPPC is rarely seen in Caucasians. Of 1001 white patients examined for palmar lesions, none fulfilled the diagnostic criteria for KPPC.9 In a study of 534 patients, Weiss et al discovered 7 cases— all in African American patients and representing 3.1% of this racial group.8
The cause of KPPC is unknown. No medications have been implicated, and it has been difficult to link it to a virus.3 Although some authors have suggested that KPPC represents flexural calluses related to manual labor, lesions also occur in patients without this history.1,5 There is no association between KPPC and arsenical agents or syphilis.8
It is generally believed that KPPC does not have a recognizable heritable pattern, though there may be exceptions.8 There may be a familial association with ichthyosis vulgaris and other disorders of keratinization. One report included 5 patients in 1 family with keratotic plugs of the palmar creases consistent with an autosomal dominant pattern of inheritance. The syndrome was associated with ichthyosis vulgaris in several family members.10 KPPP and KPPC might be the result of abnormal callus formation in predisposed individuals, as both conditions seem to be due to an abnormal hyperproliferative response to local trauma.3