A Case of Terra Firma-Forme Dermatosis: Differentiation from Other Dirty-Appearing Diseases

Dear Editor:

Terra firma-forme dermatosis (TFFD), which derives its term from the Latin phrase 'terra-firma' meaning dry land, is a rare skin disorder characterized by hyperpigmentation resembling dirt-like brown patches1, 2. Only small cases have been published, but it is important to understand this disease entity because TFFD may be relatively common in clinical practice but can be easily misdiagnosed1, 2. The patient was a 13-year-old girl with an asymptomatic dirt-like hyperpigmentation on her neck, which had been present for 2 months (Fig. 1). The lesion has not disappeared despite repetitive scrubbing with common detergents and water. She denied any history of eczema or incidents of trauma to the area, and did not use any cosmetics. No evidence of diabetes mellitus or excessive body weight was observed. The lesion was completely removed by hard scrubbing with alcohol sponges (Fig. 2). No recurrence was seen after 2 weeks of follow-up. TFFD has been largely ignored in the literature due to unawareness or indifference, but TFFD may in fact be common in clinical practice1, 2. The etiology of TFFD remains unknown, but one hypothesis demonstrates TFFD as the result of the delayed maturation of keratinocytes with melanin retention, and the accumulation of sweat, sebum, and microorganisms. This combination may lead to buildup and retention of adhesive dirt-like scales1. TFFD is easily confused with similar diseases such as dermatosis neglecta or acanthosis nigricans3. One of the point of differentiation with other diseases is TFFD usually affects children and young adults with normal hygiene habits1, 2. Additionally, TFFD mainly occurs on the face, neck, or ankles, especially posterior to the medial or lateral malleolus2. However, history of exposure to an unclean environment or underlying comorbidities causing non-washing behavior implies dermatosis neglecta, which is removable with routine detergents4. Also, TFFD can be accompanied by acanthosis nigricans in obese and diabetic patients. In these cases, TFFD can be removed by alcohol rubbing, while acanthosis nigricans remains unresolved by such measures5. Furthermore, TFFD should be distinguished from other dermatoses, including confluent and reticulated papillomatosis, pityriasis versicolor, ichthyosis, and postinflammatory hyperpigmentation1. Typical TFFD cases rarely require biopsy, but histopathological findings may aid in the diagnosis of challenging cases. Characteristic histology of TFFD demonstrates acanthosis, papillomatosis, and prominent lamellar hyperkeratosis with orthokeratotic whorls5. The recurrence of TFFD is known to be rare. Previous research has reported that more than one-fifth of patients undergo an endocrine evaluation or receive a prescription for topical corticosteroids before visiting a dermatologist2. Therefore, in typical cases of young healthy patients with a dirt-like brown appearance on the face, neck, or ankles despite normal hygiene habits, TFFD should be considered early, and alcohol scrubbing should be attempted first to prevent unnecessary diagnostic procedures and inappropriate treatments. In some cases, more aggressive efforts with alcohol were required to remove the hyperpigmentation, so vigorous force should be applied while scrubbing the lesion5. Here, we report a successfully diagnosed and treated case of TFFD. It is important for clinicians to be aware of TFFD as it is often misdiagnosed or underreported.

Fig. 1
A dirt-like hyperpigmented patch lesion on the patient's anterior neck (before alcohol swabbing).

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Fig. 2
(A) Alcohol swabs after hard scrubbing. (B) Dirt-like hyperpigmentation removed after hard scrubbing with an alcohol swab.

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