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Author: Dr Lachlan Andrew Byth, Resident Medical Officer, Ipswich Hospital, Ipswich, QLD, Australia; and Associate Lecturer, Griffith University, Southport, QLD, Australia. DermNet NZ Editor in Chief: Adjunct A/Prof. Amanda Oakley, Dermatologist, Hamilton, New Zealand. Copy edited by Gus Mitchell. October 2019.
Terra firma-forme dermatosis is a benign skin disorder that manifests as raised, dirty-appearing areas of skin. It is also called Duncan’s dirty dermatosis in honour of the dermatologist who first described it .
Terra firma is Latin for ‘dry land,’ reflecting the appearance of affected areas as islands of dirty skin. These areas are not truly dirty but give this impression due to abnormal keratinisation.
Terra firma-forme dermatosis mainly affects children and adolescents . However, there have not been any large epidemiological studies to determine how prevalent it is. It may be more common than reports suggest as it is asymptomatic, and many people are not likely to seek medical attention for it.
Terra firma-forme dermatosis is thought to be a disorder of keratinisation caused by abnormal and delayed development of skin cells. Adhesion between keratinocytes is prolonged, with retention of melanin, sebum, and microorganisms, causing the formation brown patches and thickened plaques .
It is possible that terra firma-forme dermatosis is a ‘forme fruste’ (an atypical or incomplete manifestation of another condition) of confluent and reticulated papillomatosis of Gougerot and Carteaud .
Terra firma-forme dermatosis presents with thickened, brown-black papules and plaques on the neck, trunk, face, and abdomen including the umbilicus. The plaques can have a papillomatous surface. The patient has normal washing habits.
Terra firma-forme dermatosis has been reported around surgical sites, such as after total knee replacement or median sternotomy . Rarely, it can present with extensive areas of involvement over the chest, abdomen, and thighs .
Psychosocial distress can result from the dirty appearance which may be perceived to reflect poor personal hygiene.
Terra firma-forme dermatosis is a clinical diagnosis that should be suspected in children and adolescents with dirty-appearing areas, particularly on the neck, which cannot be removed with soap.
There are several other ‘dirty dermatoses’ which mimic terra firma-forme dermatosis, including:
Other conditions to consider include:
Rubbing with ethyl or isopropyl alcohol-soaked wipes completely removes the dirty-appearing areas.
Chemical peels (eg, 20% salicylic acid in alcohol) are reported to lead to rapid resolution of the condition .
Terra firma-forme dermatosis usually responds completely to treatment and rarely recurs. Patients can be reassured this is a benign condition, and they can use alcohol wipes to remove any recurrent lesions.
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