Asymptomatic brown patches on the trunk

Abstract

A 6-year-old otherwise healthy boy presented with a one year history of asymptomatic brown patches on the trunk. The lesions were progressively spreading despite daily cleaning of the skin with soap and hot water. The eruption had been treated with antifungal cream for one month, with no improvement. Physical examination revealed brown-reticulated scaly macular plaques on the abdomen (Fig. 1). There were no other skin lesions. What is the most likely diagnosis? (Answer on page ••) Given the appearance of the lesions, terra firma-forme dermatosis (TFFD) was suspected. This diagnosis was confirmed by using the alcohol wipe test. The lesions completely disappeared after being rubbed with a 70% isopropyl alcohol-soaked gauze. TFFD, also known as Duncan's dirty dermatosis, is an underdiagnosed benign skin disorder of unknown aetiology that affects predominantly children and young adults. The condition is characterised by asymptomatic brown to black, hyperkeratotic plaques and patches with a dirt-like appearance, typically located on the trunk and skin folds (flexures of the anterior neck, axilla, cubital fossae, inguinal region and umbilical fold). Commonly, multiple sites are involved.1 The lesions are resistant to regular washing with soap and water, but can be easily removed by rubbing with 70% isopropyl alcohol or ethyl alcohol.2 The main differential diagnosis is dermatosis neglecta, a skin condition caused by poor hygiene and characterised by brown scales that can be removed with washing with soap and water. Others differential diagnoses include dirty neck syndrome, confluent and reticulated papillomatosis of Gougerot and Carteaud, acanthosis nigricans and hyperpigmented pityriasis versicolor.3 The application of 70% isopropyl alcohol is the gold standard treatment. However, in extensive cases, mild topical keratolytics may be associated in order to avoid aggressive rubbing.2