Dx: Terra firma-forme dermatosis
The physician diagnosed terra firma-forme dermatosis (TFFD) in this patient, noting the “dirty brown coloration” and distribution that did not suggest post-inflammatory hyperpigmentation or melasma. TFFD is a rare and benign form of acquired hyperpigmentation characterized by “velvety, pigmented patches or plaques.”1 A simple bedside test, known as an “alcohol wipe test,” both confirms and treats TFFD; it involves rubbing the affected area with a 70% isopropyl alcohol pad.1
TFFD typically affects the face, neck, trunk, or ankles, but the scalp, axilla, back, and pubis also can be affected.1 Histopathology will show negligible amounts of dermal inflammation, hyperkeratosis with mild acanthosis, and hyperkeratosis and papillomatosis.1 Most patients diagnosed with TFFD report that the hyperpigmentation does not improve despite washing with soap and water.2
Hygiene is not a factor
In 2015, Greywal and Cohen followed the case presentations of 10 Caucasian patients with TFFD who presented with “brown and/or black plaques or papules or both.”2 Many of the individuals followed in this case series reported “[practicing] good hygiene and showered a minimum of every other day or daily.”2 The same was reported by the patient in this case. This suggests that TFFD is not a consequence of poor hygiene but perhaps a result of “sticky” sebum that produces a buildup of keratin debris, sebum, and bacteria on the skin.3 This produces the hyperpigmentation seen clinically.
Differential includes post-inflammatory hyperpigmentation
Several other hyperpigmentation disorders were considered on the initial differential diagnosis for this case, including melasma and post-inflammatory hyperpigmentation. However, these 2 conditions are macular, whereas this hyperpigmented condition had a rough, mildly papular texture. Additionally, melasma flares up in the summer with UV exposure, and post-inflammatory hyperpigmentation presents with pruritus and/or a pre-existing rash.4 This patient reported that the condition did not itch nor change with increased sunlight, thus making melasma and post-inflammatory hyperpigmentation unlikely diagnoses.
Acanthosis nigricans also was considered because it presents with a velvety brown pigmentation similar to what was seen with this patient. Acanthosis nigricans, however, primarily affects flexural areas, not the face, making it improbable.
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