The mother of a 14-year-old girl brings the child into your clinic, essentially to gain support in her effort to convince the child to wash better. It seems that several times a year, areas of the girl’s arms and neck appear to be dirty, despite protestations of adequate washing by the patient, who will not let her mother (or anyone else, to date) scrub the areas.

The patient denies having any symptoms in the affected areas and further denies applying any medication to them. She wears no jewelry that might have touched the areas.

According to the mother and the patient, the latter is otherwise healthy. She almost never takes any medication, and she had normal blood work (including blood sugar) as part of a recent physical exam.

There is no family history of serious health problems, such as diabetes or skin diseases. The child seldom exerts to the point of perspiration, although she does swim once or twice a week for exercise.

You note that the child is moderately overweight and quite reluctant to allow anyone to see or touch the areas in question. But with considerable time and much persuasion, she allows you to examine and palpate her skin, which has a slight olive tone (type IV). The ill-defined, light brown macular discoloration stands out and indeed looks like dirt. However, it is confined to the patient’s anterior neck and lateral arms.

Although there is no palpable component to the discoloration, it has a faintly reticular look to it in places. It spares all other locations, such as the axillae, posterior neck, and back. A brief scrub with soap and water fails to have any effect on the discoloration, but a few swipes with an alcohol swab completely restore the skin to its normal, light color, effectively removing the pigmented surface. 

ANSWER

The correct answer is terra ­firma-forme dermatosis (TFFD; choice “d”), also known as “Duncan’s dirty dermatosis.” This relatively common condition usually affects adolescents and is one of the very few causes of hyperpigmentation that can be removed specifically with alcohol.

Dirty skin (choice “a”) is certainly seen, especially in this age-group, but the dirt is easily removed with soap and water.

Acanthosis nigricans (choice “b”) is often mistaken for dirty skin, but it cannot be removed by any nondestructive modality. Moreover, the most common form of acanthosis nigricans presents with a velvety, faintly raised brownish discoloration that usually affects the circumferential neck, axillae, and often, other intertriginous areas.

Reticulated and confluent papillomatosis (choice “c”) is a rare condition seen on the chest, back, and occasionally the face. It involves a slightly papular reticular (a netlike effect) patch, often in a triangular shape. Alcohol has no effect on it.

DISCUSSION
TFFD is surprisingly common, once its existence is recognized. Its etiology is, as one might expect, unknown, but it has been described in the literature (see “Suggested Reading” for examples) and is also defined by predictable histologic features seen on biopsy.

Besides the obvious implications, TFFD is probably most important as an imitator of acanthosis nigricans, which is often seen in overweight adolescents on their way to becoming diabetic. Unlike TFFD, acanthosis nigricans (type III, the most common form) has a multitude of potentially serious implications, although it is most often benign. Besides its well-known potential connection with diabetes, acanthosis nigricans can be seen in a myriad of insulin-resistant states and a bewildering variety of endocrinopathies.

SUMMARY
Unnecessary treatments and/or workups can be avoided by being aware of the existence of this common condition, which is easily diagnosed (and treated!) by wiping with alcohol—effectively ruling out the other items in the differential.

SUGGESTED READING
Duncan WC, Tschen JA, Knox JM. Terra firma-forme dermatosis. Arch Dermatol. 1987; 123(5):567-569.

Pavlovic MD, Dragos V, Potocnik M, Adamic M. Terra firma-forme dermatosis in a child. Acta Dermatovenerol Alp Panonica Adriat. 2008;17(1):41-42.