PATIENT HISTORY
A 12-year-old boy with a history of a long-standing dark brown nevus on his umbilicus presented because of recent changes in the appearance of the nevus. His parents noted that the lesion had been stable for many years but had recently increased in size. This was accompanied by a change in color around the periphery of the nevus. Washing the area using soap and water did not change the appearance of the skin lesion. The patient denied tenderness, bleeding, pruritus, and ulceration of the lesion. Physical examination revealed a well-demarcated, symmetric, 2 x 2 mm medium- to dark-brown macule on the umbilicus surrounded by a yellowish-tan, hyperkeratotic plaque (Figure 1). No other atypical skin lesions were identified on a total body skin examination.
Multiple-Choice Question
What is the next best step in this patient's management?
A. Perform a shave biopsy
B. Rub the area with alcohol
C. Perform a scraping for a potassium hydroxide (KOH) prep test
D. Perform an excisional biopsy with a narrow margin
E. Evaluate the patient for hyperinsulinemia
Answer
The answer is B: Rub the area with alcohol.
DISCUSSION
Terra firma-forme dermatosis (TFFD), or retention hyperkeratosis, is a benign condition characterized by asymptomatic, yellow-brown patches or plaques that are resistant to washing with soap and water but easily cleared using 70% isopropyl alcohol. TFFD does not have a predilection of gender or race/ethnicity and most commonly affects the neck, axilla, naval, and trunk of children and young adults. The pathogenesis of TFFD has been proposed to be related to altered keratinocyte maturation (Sechi et al., 2021).
Clinically, TFFD can be difficult to distinguish from dermatosis neglecta (DN), which similarly appears as brown scaly plaques and may also be removed upon scrubbing with isopropyl alcohol. DN is due to inadequate scrubbing of the skin that results in accumulation of adherent scales (Saha et al., 2015). Unlike TFFD, DN may be cleared with regular washing with soap and water.
Other clinical differential diagnoses include pityriasis versicolor, confluent and reticulated papillomatosis, seborrheic keratosis, and acanthosis nigricans. Clinical correlation in conjunction with skin examination findings assists the differentiation of these conditions. Pityriasis versicolor is a superficial mycosis because of Malassezia yeast that presents as hypopigmented or hyperpigmented, scaly macules. Clinically, pityriasis versicolor tends to occur in warm and humid environments and affects the upper trunk, arms, neck, and face (Karray & McKinney, 2022). KOH staining in pityriasis versicolor reveals hyphae and spores in a characteristic "meatballs and spaghetti" pattern, whereas KOH staining is negative in TFFD (Karray & McKinney, 2022; Sechi et al., 2021). Acanthosis nigricans appears as hyperpigmented, velvety plaques arising in body folds associated with underlying hyperinsulinemia, endocrine dysfunction, or malignancy (Das et al., 2020). Confluent and reticulated papillomatosis has a predilection for young women with darker skin phenotypes and is characterized by brown papules arranged in a reticulated pattern in the epigastric, inframammary, and interscapular areas (Scheinfeld, 2006). Seborrheic keratoses present in older adults as "stuck-on" tan-brown macules that become increasingly raised and verrucous. An alcohol rubbing test is negative in these cases (Hafner & Vogt, 2008).
The occurrence of TFFD near nevi may be mistaken for malignant changes in shape, color, and size of the nevi. The combination of clinical findings with dermoscopic examination is helpful to distinguish malignant melanoma from TFFD, which appears on dermoscopy as brown polygonal plate-like scales arranged in a mosaic pattern (Errichetti & Stinco, 2017). A positive alcohol rubbing test, diagnostic of TFFD in these cases, may also prevent unnecessary biopsies, which may contribute to increased anxiety and risk for bleeding, infection, and scarring (Matthews et al., 2019). Although biopsy with microscopic evaluation is unnecessary in TFFD, histopathologic features include prominent lamellar hyperkeratosis, whorled orthokeratosis, acanthosis, papillomatosis, and hypermelanosis in the basal layer (Sechi et al., 2021).
In the current case, rubbing the naval skin with alcohol removed the new rim of light brown material surrounding the preexisting nevus. A subsequent dermoscopic examination revealed only the original nevus with benign features.
In conclusion, medical professionals should recognize TFFD as a common, benign condition in children and adults. In conjunction with clinical correlation, the alcohol rubbing test and dermoscopic examination are helpful, noninvasive methods of distinguishing TFFD from other diagnoses. Accurate diagnosis and treatment of TFFD using the alcohol rubbing test may prevent unnecessary biopsy in cases of suspected malignancy.
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