INTRODUCTION

Terra firma-forme dermatosis (TFFD), first described by Duncan and colleagues in 1987, is an acquired benign disorder of keratinization characterized by asymptomatic brown-to-black plaques that resemble dirt and cannot be removed with routine washing using soap and water [1]. The condition is thought to result from delayed keratinocyte maturation and retention of melanin, sebum, microorganisms, and compact keratin within the epidermis [2].

Because of its unusual appearance, TFFD is frequently misdiagnosed as acanthosis nigricans, pityriasis versicolor, dermatosis neglecta, confluent and reticulated papillomatosis, or post-inflammatory hyperpigmentation [3]. Recognition of the characteristic response to alcohol swabbing is essential, as this simple bedside maneuver is both diagnostic and therapeutic [4].

CASE REPORT

A 47-year-old man presented to our dermatology clinic with an asymptomatic hyperpigmented lesion involving the left supraclavicular and upper chest region. The lesion had been present for more than one year and had progressively become a source of cosmetic concern.

The patient reported consultation with several dermatologists during the preceding year. He had received multiple treatments, including topical corticosteroids, topical antifungal agents, and oral antifungal therapy, without any clinical improvement. Previous diagnoses included acanthosis nigricans and superficial fungal infection. No diagnostic investigations had been performed.

Dermatological examination revealed a unilateral brown reticulated hyperpigmented plaque with a dirty appearance over the left supraclavicular area extending to the upper chest (Fig. 1a). The lesion was asymptomatic and showed no signs of inflammation or scaling.

Figure 1: (a) Brown reticulated hyperpigmented plaque with a dirty appearance involving the left supraclavicular and upper chest region before treatment. (b) Alcohol swab test demonstrating removal of pigmented keratinous debris onto the gauze pad. (c) Near-complete disappearance of the lesion immediately after rubbing with 70% isopropyl alcohol, confirming the diagnosis of terra firma-forme dermatosis.

Based on the clinical morphology, terra firma-forme dermatosis was suspected. The lesion was rubbed with 70% isopropyl alcohol using a gauze pad. Immediate removal of the pigmented material was observed, with visible brown debris transferred onto the gauze (Fig. 1b). Following alcohol swabbing, the lesion cleared almost completely, revealing normal underlying skin and confirming the diagnosis of terra firma-forme dermatosis (Fig. 1c).

No further treatment was required, and the patient was reassured regarding the benign nature of the condition.

DISCUSSION

Terra firma-forme dermatosis is likely underdiagnosed despite being relatively common in dermatological practice [2]. The condition may affect both children and adults and most frequently involves the neck, trunk, face, and flexural areas [5].

The exact pathogenesis remains uncertain. Current evidence suggests abnormal keratinization with retention of keratinocytes, melanin, sebum, and microorganisms leading to the formation of adherent hyperpigmented plaques that resist normal cleansing [2,5].

The principal differential diagnoses include acanthosis nigricans, dermatosis neglecta, pityriasis versicolor, confluent and reticulated papillomatosis, epidermal nevi, and post-inflammatory hyperpigmentation [3,6]. Distinguishing TFFD from acanthosis nigricans is particularly important because the latter may prompt extensive metabolic investigations, whereas TFFD can be diagnosed immediately by a simple alcohol swab test [4].

Our patient illustrates the diagnostic difficulties associated with TFFD. For more than one year, the lesion was repeatedly misdiagnosed and treated with multiple topical and systemic medications without improvement. The diagnosis was ultimately established within seconds using the alcohol swab test, avoiding unnecessary investigations and further ineffective treatments.

The alcohol swab test, often referred to as the SMART (Skin Modified by Alcohol Rubbing Test), remains the cornerstone of diagnosis [4]. Removal of the lesion after vigorous rubbing with 70% isopropyl alcohol is considered pathognomonic and simultaneously therapeutic.

This case emphasizes the importance of including TFFD in the differential diagnosis of persistent hyperpigmented plaques, particularly when conventional treatments fail, and the lesion displays a characteristic dirty appearance.

CONCLUSION

Terra firma-forme dermatosis should always be considered in patients presenting with persistent dirty-appearing hyperpigmented plaques. A simple alcohol swab test can rapidly establish the diagnosis, prevent unnecessary investigations and treatments, and provide immediate therapeutic benefit. Awareness of this easily overlooked condition remains essential for dermatologists and primary care physicians alike.

REFERENCES

1.  Duncan WC, Tschen JA, Knox JM. Terra firma-forme dermatosis. Arch Dermatol. 1987;123:567-9.

2.  Berk DR. Terra firma-forme dermatosis:a retrospective review of 31 patients. Pediatr Dermatol. 2012;29:297-300.

3.  Martin-Gorgojo A, Alonso-Usero V, Gavrilova M. Terra firma-forme dermatosis:clinical and diagnostic considerations. Actas Dermosifiliogr. 2012;103:932-4.

4.  Erkek E, Sahin S, Cetin ED, Sezer E. Terra firma-forme dermatosis. Dermatology. 2004;208:234-5.

5.  Akkash L, Badran D, Al-Omari AQ. Terra firma-forme dermatosis:a clinical entity frequently misdiagnosed. J Dermatol Case Rep. 2009;3:36-9.

6.  Berk DR, Bayliss SJ. Terra firma-forme dermatosis and dermatosis neglecta:similarities and differences. Pediatr Dermatol. 2010;27:285-9.