A Hyperpigmented Patch That Remains Despite Washing With Soap and Water

Answer: Terra Firma-Forme Dermatosis

Terra firma-forme dermatosis (TFFD) is an acquired, idiopathic, benign dermatosis characterized by an asymptomatic brownish gray or black dirtlike patch that cannot be removed with ordinary cleansing but can be removed by wiping with isopropyl alcohol or ethyl alcohol.^1,2 The term is derived from the Latin phrase terra firma, meaning “dry land,” thus implying dirtlike dermatosis or dirty skin.^2,3 The condition was first described by Christopher Duncan and colleagues in 1987,⁴ hence it also has been called “Duncan’s dirty dermatosis.” Recognition of this benign and easily treated condition is important so that unnecessary investigations and treatments can be avoided.

Epidemiology

Epidemiologic data on the prevalence and incidence of TFFD are lacking, given that this condition is underreported and that systematic studies on it are limited. TFFD affects individuals of all age groups but is most frequently seen in prepubertal children and adolescents.^4-9

Aslan and colleagues performed a retrospective chart review of patients seen between June 2013 and February 2016 at the Department of Dermatology of the Kocaeli University in Turkey and identified 79 patients with TFFD.¹⁰ Of the 79 patients, 70 were children (aged 1 to 17 years) and 9 were adults (aged 18 to 42 years).

Between January 1 and February 1, 2017, Neri and colleagues prospectively enrolled 137 consecutive patients referred for the first time to the pediatric dermatology outpatient clinic of the University of Bologna in Italy.⁷ These patients were evaluated for the presence of TFFD and for the presence or personal history of other dermatoses. Of the patients enrolled, 49 (38.5%) had TFFD and 68 (49.6%) had atopic dermatitis. The authors found a significant association between TFFD and atopic dermatitis, since 44% of patients affected by atopic dermatitis also had TFFD. In contrast, only 27.5% of patients not affected by atopic dermatitis had TFFD (odds ratio, 2.08; 95% CI, 1.019-4.238). Although the results cannot be generalized, since the study population was small and highly selected, Neri and colleagues’ study showed that TFFD is common in children.

It is believed that TFFD is more common than is generally appreciated due to underrecognition and underreporting of this benign condition.³ The sex incidence is approximately equal.^9,11,12 The condition is more common during the summer months.¹³

Etiopathogenesis

The exact etiopathogenesis is not known. The condition is believed to result from delayed maturation of keratinocytes with incomplete development of keratin squames, and retention of keratinocytes and melanin within the epidermis.^1,4-6,9,14 Accumulation of residues of sebum, sweat, and scales may lead to buildup and compaction of dirtlike scales.^9,14 Atopic dermatitis may be a predisposing factor, since atopic dermatitis is characterized by epidermal barrier defect and the observation of a high prevalence of atopic dermatitis in patients with TFFD.^6,7,15 Berk identified 31 patients with TFFD seen over 17 months of whom 12 (38.7%) also had atopic dermatitis.⁶ In the study by Aslan and colleagues, 6 (7.6%) of 79 patients with TFFD also had atopic dermatitis.¹⁰ There might be a genetic predisposition to TFFD, since familial cases, although rare, have been reported.¹⁰

Histopathology

Histopathologic findings include lamellar hyperkeratosis with focal areas of compact whorled orthokeratosis, papillomatosis, acanthosis, and keratin globules in the stratum corneum.^2,9,10,16-18 Parakeratosis is not observed.^16-18

Clinical Manifestations

Typically, TFFD presents with an asymptomatic, brownish gray or black, dirtlike patch or plaque.^1-3,11 The lesion may appear reticulated, hyperkeratotic, papillomatous, verrucous, or stuck on.^11,13,17,19 Characteristically, the lesion cannot be removed by conventional washing with water and soap but can be easily removed by wiping or rubbing with ethyl alcohol or isopropyl alcohol.^1,3,20 Affected individuals often have normal hygiene habits.^1,11,17,19 Sites of predilection include the neck and navel, followed by the malleoli, trunk, and face, although the arms, knees, legs, axillae, and scalp can also be involved.^3-9 The lesion is usually localized but can be extensive or generalized.^10,13 Freemyer and colleagues reported the case of a 46-year-old woman with TFFD presenting as a linear, hyperkeratotic, dark brown plaque on the midline back extending from the top of the sacrum to the upper back.²¹

Diagnosis

The diagnosis is often suspected based on its distinctive clinical features. Dermoscopy typically shows large, polygonal, platelike, brown scales in a mosaic, cobblestone, or tie-like pattern interrupted in furrows.^16,18 The diagnosis can be confirmed by wiping or rubbing the lesion with an alcohol-soaked gauze, pad, or cotton ball, which results in resolution of the lesion.^1,5,9,11,22 This is known as the Skin Modified by Alcohol Rubbing Test (SMART).²³ A biopsy is not required for diagnosis.

Differential Diagnosis

The main differential diagnoses are dermatosis neglecta and acanthosis nigricans. Dermatosis neglecta typically affects individuals of any age with neglected hygiene.¹ The brownish, hyperkeratotic, verrucous crusts and cornflake-like scales, often symmetrically distributed, result from progressive accumulation of sebum, cellular debris, keratin, sweat, and exogenous impurities.^22,24 Unlike TFFD, these lesions can be removed with normal washing with soap and water as well as with an alcohol swab or cotton ball.^16,25 The classic lesion of acanthosis nigricans consists of dark, velvety thickening of the skin, usually on the nape and sides of the neck, as well as the axillae and inner thighs. The lesion typically presents in a symmetric fashion. There is no melanin deposition. Rather, the pigmentation is mainly due to hyperkeratosis. The condition is most commonly caused by obesity, although there are several other possible causes. The hyperpigmentation or “dirt” cannot be removed either by normal washing with soap and water or alcohol swab or cotton ball.

Other differential diagnoses that present with hyperpigmentation of the skin include ephelides, lentigo simplex, confluent and reticulated papillomatosis, postinflammatory hyperpigmentation, frictional lichenoid eruption, pityriasis versicolor, ichthyosis vulgaris, erythema dyschromicum perstans, phytophotodermatitis, and Becker nevus.^16,17 The distinctive features of each condition and the fact that none of these conditions can be cleared by wiping with water or alcohol allow a straightforward differentiation from TFFD.

Ephelides typically present as small, well-demarcated, hyperpigmented macules, usually 1 to 2 mm, on a sun-exposed area such as the face.²⁶ The lesions are tan, slightly red, or light brown. The onset is usually in the first few years of life and is more common in individuals with red or blond hair and fair skin complexion (Fitzpatrick phototypes I and II).²⁶ Characteristically, ephelides become darker during the summer and tend to fade in the winter.

Lentigo simplex (simple lentigines) are hyperpigmented macules that are larger and darker than ephelides.²⁶ Although simple lentigines are also more commonly observed on sun-exposed areas, they do not usually fade during the winter. Lentigo simplex may appear during childhood, but solar lentigines are more common after the age of 50.

Confluent and reticulated papillomatosis is an acquired ichthyosiform dermatosis characterized by persistent, asymptomatic, dark, scaly, macules and patches that tend to be confluent in the center and reticulated at the periphery and localized predominately on the trunk.²⁷ Initially, the lesions present as small, round, erythematous, flat-topped, hyperkeratotic or verrucous papules or macules. These papules or macules gradually enlarge to 4 to 5 mm and coalesce to form confluent slightly scaly patches or plaques centrally and a reticular pattern peripherally. Over time, the color of the lesions becomes brown or dull brown.

Postinflammatory hyperpigmentation, also known as postinflammatory melanosis, develops as a sequela of a variety of insults to the skin, such as inflammatory diseases (eg, atopic dermatitis, acne vulgaris), trauma, and chemical or physical injuries. The condition is more common in dark-skinned individuals. Postinflammatory hyperpigmentation presents as hyperpigmented macules/patches in the area of the preceding inflammatory dermatosis or injury. The color tends to be tan to light brown if the excess pigment is within the epidermis. If the excess pigment is in the dermis, the color is usually blue or dark gray.

Frictional lichenoid eruption typically presents as lichenoid, reddish or skin-colored papules, mainly seen on the elbows and knees. It is also commonly found on the extensor surfaces of the forearms. The papules have regular borders, are 1 to 2 mm in diameter, and sometimes aggregate in plaques. Inquiry may reveal contact with irritant or abrasive materials such as sand, grass, or wool blankets.

Pityriasis versicolor, also known as tinea versicolor, is a superficial infection of the skin caused by dimorphic lipid-dependent yeasts in the genus Malassezia (formerly known as Pityrosporum), notably Malassezia globosa. Pityriasis versicolor is characterized by scaly hypopigmented or hyperpigmented macules/patches, most commonly affecting areas of skin that are rich in sebum production, such as the upper arms, neck, and trunk. Typically, lesions arise as multiple small, circular macules that enlarge radially and coalesce into patches. The eruption varies in color from patient to patient, but each person’s lesions are of a single hue. In general, hyperpigmented red to brown lesions erupt in fair-skinned patients, whereas those with dark skin tend to have hypopigmented lesions. The lesions are covered with a fine scale and are typically asymptomatic, although some patients experience mild pruritus.

The lesions of ichthyosis vulgaris appear in most patients during the first year of life and in the vast majority by age 5 years.²⁸ The scaling is symmetric and usually intensifies until puberty and subsequently decreases with age. The color of the fine, fishlike scales varies from white to dirty gray to brown. In general, darker scales are seen in dark-skinned persons.²⁸ The lesions can vary from barely visible roughness and dryness to strong, horny plates. The lesions tend to improve during the summer and with increasing humidity and to worsen during the winter, when some patients report “lizard-like” skin.²⁸ Scaling is most prominent on the extensor aspects of the extremities, particularly the shins. The scales often curl up at the edges, which imparts a rough feel to the skin.

Erythema dyschromicum perstans, also known as ashy dermatosis, is an acquired, chronic pigmentary disorder characterized by slowly progressive, asymptomatic, ashy gray-colored macules/patches distributed symmetrically on the trunk and proximal extremities.²⁹ The onset is insidious, and the lesions are slowly progressing in size and number. The size of the lesions ranges from a few millimeters to several centimeters in diameter. A slightly raised, erythematous border may be present in the early stage, which is characteristic when present.²⁹ The erythematous border resolves with time.

Phytophotodermatitis refers to a nonimmunologic photosensitive dermal reaction induced by the contact to a photosensitive substance found in certain plants, followed by exposure to sunlight. A phototoxic inflammatory eruption typically occurs 24 hours after the exposure of the skin to a furocoumarin and sunlight, with a peak at 30 to 120 minutes. Clinically, this is manifested as bizarre configurations of erythema with a sharply demarcated border confined to the area that has come in contact with the offending plant agent and consequent sun exposure. A burning sensation and pain are prominent. Vesicles and bullae may develop after 24 hours and peak at 72 hours and are often accompanied by subsequent desquamation and denudation. Pruritus does not seem to be common. Hyperpigmentation often develops 1 to 2 weeks later and can appear in bizarre streaks or droplike patterns where the furocoumarin contacts the sun-exposed skin. Phytophotodermatitis is most common on uncovered sites exposed to sunlight and plants such as arms and legs.

Clinically, a Becker nevus presents as an asymptomatic, circumscribed, light to dark brownish macule or patch that gradually enlarges in an irregular fashion, similar to a geographical configuration. The hyperpigmentation may appear as a single irregular hyperpigmented macule/patch or multiple blotchy hyperpigmented macules arranged in a checkerboard pattern. If hypertrichosis develops, it occurs a few years after the pigmentation. The hairs generally appear in the region of the pigmentation but are not necessarily confined to that area; they become coarser and darker with time. Nonhairy Becker nevi account for approximately 50% of cases. Sites of predilection include the shoulder, scapula, and upper chest.