[Clinicopathological aspects of terra firma-forme dermatosis]

Terra firma-forme dermatosis was first described in 1987. It is characterized by the appearance in children or adolescents of dirt-like patches despite normal cleansing. The lesions are removed when the skin is rubbed with a 70°C alcohol swab. This largely unknown condition is of uncertain origin but could be due to a keratinisation disorder.

Herein we report the case of a 17-year-old male patient who, after seeking the opinions of a number of doctors, consulted in dermatology for multiple pigmented patches on the trunk and limbs that had appeared one year earlier. These lesions had persisted despite appropriate cleansing. He had no history of endocrine disorders and no familial history of pigmentation disorders. A skin biopsy revealed compact orthokeratotic hyperkeratosis resembling a second layer of stratum corneum on top of a normal layer. Very small granules were seen within this layer and PAS staining revealed spores. These skin lesions disappeared when rubbed with an alcohol swab, resulting in a diagnosis of terra firma-forme dermatosis.

Where a diagnosis of terra firma-forme dermatosis is suspected, confirmation is easy to obtain using an alcohol swab. Nevertheless, the disease is not familiar to dermatologists. The most common differential diagnoses are acanthosis nigricans, reticulate and confluent papillomatosis, and Dowling-Degos disease. Their histopathological appearances are very different and skin biopsy can be useful for diagnosis. These entities belong to a group of disorders involving abnormal keratinisation and pigmentation. Anatomoclinical correlation is essential for optimal management. The appearance of the stratum corneum may play an important role in the diagnosis of terra firma-forme dermatosis.