Derm Dx: ‘Dirty’ skin that cannot be washed


  • Terra firma-forme dermatosis 1_0213 Derm Dx

  • Terra firma-forme dermatosis 2_0213 Derm Dx

  • Terra firma-forme dermatosis 3_0213 Derm Dx

A 50-year-old black male complains of brown spots on his back. He is unsure how long they have been there. The patient’s wife has tried washing them off with soap and water, but they cannot be removed. His past medical history is significant for type 2 diabetes, obesity and hypertension.

A complete physical exam is significant for brown black macules and papules on his back. Although simple soap and water did not work, vigorously rubbing the lesions with isopropyl alcohol was able to remove them (pictured).

Terra firma-forme dermatosis is also called "Duncan's dirty dermatosis" after W. Christopher Duncan, MD, who first described the condition in 1987.. It is characterized by a dirt-like and brown discoloration of the neck, trunk and/or limbs that cannot be removed...

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Terra firma-forme dermatosis is also called “Duncan’s dirty dermatosis” after W. Christopher Duncan, MD, who first described the condition in 1987.. It is characterized by a dirt-like and brown discoloration of the neck, trunk and/or limbs that cannot be removed with soap and water. 

The disorder is most commonly seen on the necks of children. However, terra firma-forme dermatosis may also affect adults, and the case presented here is quite a dramatic example. 

Rubbing affected areas vigorously with 70% isopropyl alcohol will remove the discoloration, but unfortunately the problem recurs frequently.

Terra-firma forme dermatosis is readily distinguished from macular amyloidosis, acanthosis nigricans and confluent and reticulated papillomatosis, since none of the latter dermatoses can be removed with alcohol. On histology, terra firma-forme dermatosis demonstrates hyperkeratosis with keratin globules in the stratum corneum.

Patients with acanthosis nigricans clinically present with hyperpigmented plaques that have a characteristic velvety texture. The lesions are distributed symmetrically and may involve multiple regions including the neck, face, groin, elbows, knees, extensor aspect of the finger joints, areolae and umbilicus. There may be oral mucosal involvement.

Obesity, even in the absence of a detectable endocrinologic abnormality, is the single most common association with acanthosis nigricans. Clinical diagnosis is based on the presence of velvety hyperpigmented plaques in the typical distribution pattern.

When the diagnosis is in doubt a punch biopsy may be performed. The histopathology will show papillomatosis and hyperkeratosis. Ironically, acanthosis is not present on histology.

Confluent and reticulated papillomatosis (CARP) is a rare disorder that typically begins in puberty. Females and blacks are about twice as likely to be affected than white males.

Initially patients with CARP present as small papules, usually appearing in the intermammary, epigastric or interscapular region. The lesions enlarge and become hyperpigmented. Centrally, they coalesce and become confluent. At the periphery, they have a reticulated morphology.  Lesions are usually asymptomatic, but rarely patients complain of itch. 

Patients with macular amyloidosis present with pruritic, rippled, brown macules, most commonly on the interscapular back. The etiology is believed to be chronic scratching. 

Diagnosis & Treatment

Terra firma-forme dermatosis is based on the clinical appearance of “dirty” skin that cannot be cleansed with soap and water, but improves when vigorously rubbed with 70% isopropyl alcohol. Biopsy is rarely performed. 

Adam Rees, MD, is a graduate of the University of California Los Angeles School of Medicine and a resident in the Department of Dermatology at Baylor College of Medicine in Houston.


  1. Duncan WC et al. Arch Dermatol. 1987;123(5):567-569.
  2. Bolognia J, Jorizzo JL, Rapini RP. Dermatology. “Chapter 52: Dermatologic Manifestations in Patients with Systemic Disease.” St. Louis, Mo.: Mosby/Elsevier, 2008.
  3. James WD, Berger TG, Elston DM et al. Andrews’ Diseases of the Skin: Clinical Dermatology. ” Chapter 24: Endocrine Diseases.” Philadelphia: Saunders Elsevier, 2006.
  4. Schachner LA, Hansen RC. Pediatric Dermatology. 4th Edition. “Chapter 10: Pigmentary abnormalities.” St. Louis, Mo.:  Mosby Elsevier, 2011.
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