Symmetrical acral keratoderma revisited: proposal for a new term, 'pigmented carpotarsal hyperkeratosis'

First reported from Taiwan mistakenly as acral acanthosis nigricans in 1991, pigmented carpotarsal hyperkeratosis or hyperkeratosis nigricans carpi et tarsi displays a peculiar distribution of velvety brown-grey hyperpigmented plaques symmetrically on the flexural side of the wrists and ankles and on the dorsal sides of the hands and feet. A marked epidermal hyperkeratosis with typically mild acanthosis and papillomatosis is observed in histology. Whitish maceration upon perspiration or water exposure, with exacerbation in summer but remission in winter, is common. The association with obesity, endocrine disorders, atopic dermatitis, ichthyosis or malignancy is unknown. Familial occurrence and hereditary patterns are ill-defined. There is preliminary evidence indicating a pathogenic role of missense mutation in the transcription factor 4 gene. Treatment is empirical, with good outcome with topical retinoids and keratolytic agents. Recurrence is common, and long-term prognosis is unclear. To be distinguished are acral acanthosis nigricans, palmoplantar keratoderma of the Nagashima type, palmoplantar keratoderma of the Bothnian type and aquagenic palmoplantar keratoderma. Most reported cases are from Southern China and are predominantly observed in men between the ages of 20 and 40 years. The currently used term 'symmetrical acral keratoderma' is non-specific and misleading and may lead to global unawareness, underreporting or misdiagnosis of this phenomenon. Further genetic and molecular studies are required to clarify its pathogenesis and relation to palmoplantar keratoderma.