Terra firma-forme dermatosis

A 73-year-old man presented to the dermatology clinic with a 10-day history of blackish lesions on his chest. The patient had no history of atopy and reported regular bathing habits. Physical examination revealed multiple blackish papules on the chest [Figure 1a]. On close-up inspection, some lesions were annular in shape. A dermoscopy of the lesions showed brown to blackish perifollicular hyperpigmentation with sparing skin creases [Figure 1b]. The lesions did not disappear after washing with water; however, forceful rubbing with a gauze pad soaked in 70% isopropyl alcohol resulted in the complete clearance of the lesions [Figure 1c]. With confluent and reticulated papillomatosis, pityriasis versicolor, porokeratosis, and dermatitis neglecta as differential diagnoses, a final diagnosis of terra firma-forme dermatosis was made. Terra firmaforme dermatosis is differentiated from dermatitis neglecta by the presence of adequate hygiene in the patient and successful clearance of the lesion with 70% isopropyl alcohol. Also known as Duncan’s dirty dermatosis, it is a cutaneous pigmentation disorder characterized by brown-gray, pigmented patches or plaques, commonly affecting the face, neck, trunk, and ankles. It is hypothesized to result from delayed maturation of keratinocytes, leading to retention of keratinocytes and melanin within the epidermis. Dermoscopic patterns seen in Terra firmaforme dermatosis includes polygonal brown clods, seborrheic keratosis-like, and perifollicular hyperpigmentation.^[1] Although not usually performed, a skin biopsy would reveal melanin retention and alterations in keratinization.^[2] During a telephonic follow-up two months later, the patient reported that the lesions had not recurred. It is important to convey the patient regarding the benign nature of the dirty pigmentation to the patient as it is generally considered a cosmetic concern.

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Figure 1

(a): Physical examination showing multiple blackish, barely elevated papules on the chest, with few annular shaped lesions; (b): Dermoscopy of the lesions showing brown to blackish perifollicular hyperpigmentation (arrow) with sparing of skin creases (DermLite DL200 hybrid, polarized light, ×10); (c): Forceful rubbing with a gauze pad soaked in 70% isopropyl alcohol resulting in the complete clearance of the lesions.

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