Answer: A

Terra firma-forme dermatosis (TFFD), or Duncan disease, was first described in 1987 by W. Christopher Duncan, MD.1 It is an asymptomatic condition characterized by dirt-like, hyperpigmented plaques most commonly distributed on the neck, axilla, and trunk.1 These plaques are resistant to regular washing, often leading to the clinical presentation described as “dirt” that cannot be cleaned off.1  It most frequently occurs in children and adolescents with good hygiene habits.2 There are no known predisposing risk factors, TFFD is neither life-threatening nor contagious, and currently a pathogenic cause has not been identified.2 Although primarily a cosmetic concern, there is a high potential for unnecessary diagnostic testing and therapeutic procedures such as biopsies and blood work.3 Therefore, it is important to note that the hyperpigmented plaques in TFFD are easily distinguishable from other conditions as they can easily be rubbed off with 70% isopropyl alcohol.1

TFFD appears as light-to-dark brown, slightly elevated hyperpigmented plaques that are frequently described as “dirt like”.1-5 Patients or their parents will commonly report that the plaques are resistant to rigorous washing and scrubbing.2 These lesions can present anywhere on the body, most commonly occurring on the neck, axilla, trunk, face, scalp, and ankles.2 Currently, there is no consensus regarding the existence of predisposing risk factors. However, individual case reports have indicated emollients and sun exposure as potential causative agents. These finding are controversial as conflicting case reports have found this not to be true, describing lesions that can occur on non-sun-exposed regions of the trunk.3,6 TFFD affects both sexes equally, and with most patients being young adults and children, lesions are often first noticed by parents.3

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The precise cause of TFFD has yet to be elucidated. Some case reports indicate Malassezia furfur spores in the basal layer as the causative agent; however, malassezia can be found in any hyperkeratotic skin lesion as part of the normal flora and is not always a pathogenic organism.7 Most often, cultures from the hyperpigmented lesions are negative for bacterial and fungal species and reveal only normal flora, indicating a noninfectious cause.3

Histologically, thick keratin globules can be found throughout the stratum corneum as well as increased melanin in compact hyperkeratotic areas.1 Additionally, areas of abundant melanin pigment with areas of anucleated keratin may also be observed.1,3,4 These changes suggest incomplete keratin development since both large amounts of melanin and desmosomal attachments are retained. This failure in development then leads to the hyperkeratosis and hyperpigmentation that results in the development of the characteristic lesions seen on presentation.1,3,4

The differential diagnosis for TFFD includes a variety of dermatologic diseases, all of which are characterized by hyperpigmented plaques. These include pityriasis versicolor, acanthosis nigricans, epidermolytic hyperkeratosis, idiopathic deciduous skin, dermatosis neglecta, seborrheic keratosis, and confluent and reticulated papillomatosis.1,3 The ability to remove the hyperpigmented lesions with soap and water suggests a diagnosis of dermatosis neglecta rather than TFFD.5,8  Most of the other diseases in which hyperpigmented plaques can be found have individual diagnostic criteria, some of which include: positive cultures or fungal stains (pityriasis versicolor, seborrheic keratosis), the presence of systemic disease associated with insulin resistance (acanthosis nigricans), or the presence of one or more clinical criteria (confluent and reticulated papillomatosis). However, TFFD is uniquely identified and diagnosed by the ability to resolve the skin lesions through the application of 70% alcohol to the affected area.

The diagnostic and treatment modalities for TFFD are the same: the application of 70% alcohol to the affected area with subsequent removal of the hyperpigmented plaque from the patient’s skin both confirms the diagnosis as well as treats the condition. Although most cases can be resolved by gentle application of the alcohol solution, some may require more vigorous rubbing.9 Because there have not been any identified predisposing risk factors, no changes in daily hygiene habits or cutaneous exposures are required. Recurrences are rare, but patients may choose to prophylax against the development of further lesions by wiping previously affected skin with 70% alcohol.3 Other less common treatment methods that have been reported include topical antifungal agents, topical steroids, and urea cream.7 How these treatments clear skin affected by TFFD is unclear. For sensitive skin for which 70% alcohol may be irritating, salicylic acid alcohol has been reported as an alternative. The efficacious nature of this intervention is likely due to the combination of the alcohol with the keratolytic feature of the salicylic acid.7

Overall, it is important to remember that the lesions of TFFD appear as hyperpigmented plaques that occur most commonly in the axilla, neck, and trunk. These lesions often present in childhood and can easily be removed with the application of a 70% alcohol solution. TFFD should always be considered in patients presenting with new-onset hyperpigmented plaques to avoid unnecessary diagnostic procedures for a disease for which the treatment is simple, quick, and effective.

The patient in this case was suspected of having TFFD given the characteristic appearance and location of the lesions, as well as the fact that they had failed to subside with soap and water scrubs. The diagnosis was confirmed after resolution of the lesions upon rubbing the affected areas with 70% isopropyl alcohol pads.

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Case 2

A 26-year-old man presented to the dermatology clinic with a 1-year history of an unresolving rash. The rash began as small brown papules on his neck that slowly grouped and progressed across his neck and chest. He denied any other systemic symptoms. There is no family history of similarly appearing rashes. Examination of the skin revealed multiple brown, hyperpigmented plaques distributed across his neck and upper chest. Previous treatment with antifungal therapy did not improve the rash. Routine blood work at his last primary care appointment did not reveal any abnormalities. Shave biopsy revealed epidermal hyperkeratosis, papillomatosis, and acanthosis.

Can you diagnose the condition in Case 2?

A. Acanthosis nigricans

B. Confluent and reticulated papillomatosis

C. Dowling-Degos disease

D. Galli-Galli disease

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