Terra firma-forme dermatosis
TFFD is the result of disordered and delayed keratinization of an unknown etiology. TFFD may appear anywhere on the body but is commonly found on the neck, axilla, and trunk. While it occurs more frequently in children and adolescents, it can be found in adults. There are currently no known predisposing risk factors (including age, race, sex, geography, medications, or comorbidities). Although not a life-threatening or contagious condition, it can lead to unnecessary tests (biopsies, endocrine evaluations, etc) and can be cosmetically bothersome for individuals unable to achieve clean-appearing skin.
L85.9 – Epidermal thickening, unspecified
277905003 – Disorder of keratinization
Differential Diagnosis & Pitfalls
- Dermatosis neglecta – Accumulation of hyperpigmented and adherent scales due to inadequate cleaning or scrubbing of the skin. Often due to underlying physical disability or prior trauma leading to areas going unwashed. Lesions can be removed with vigorous rubbing with soap and water, often repeated over the course of multiple weeks. Dermatosis neglecta may also clear with rubbing of 70% alcohol. When the lesion has persisted in the context of regular washing, TFFD is suggested.
- Acanthosis nigricans – Brown, velvety plaques arising in the body folds, often serving as a marker of hyperinsulinemia secondary to insulin resistance in obese patients. Treatment of the underlying cause, such as weight, endocrine dysfunction, or underlying malignancy, will reverse skin changes. Acanthosis nigricans does not respond to rubbing with isopropyl alcohol. With acanthosis nigricans, acrochordons (skin tags) are frequently present in involved areas.
- Pityriasis versicolor – Superficial mycosis from yeast of genus Malassezia, often presenting in warm and humid environments. Pityriasis versicolor can appear as either hyper- or hypopigmented macules. Potassium hydroxide (KOH) prep reveals hyphae and spores, commonly referred to as "spaghetti and meatballs." Pityriasis versicolor responds to topical imidazole or selenium sulfide agents. It does not respond to rubbing with isopropyl alcohol.
- Seborrheic keratosis – Benign epidermal keratinocyte proliferation that is nearly ubiquitous in older adults. In its early stages, seborrheic keratosis present as small, flat to slightly raised, tan or brown macules that look similar to TFFD. Over time they become increasingly verrucous and elevated, developing a familiar "stuck-on" appearance. While no treatment is necessary, they are easily curetted off. Seborrheic keratosis does not respond to rubbing with isopropyl alcohol.
- Confluent and reticulated papillomatosis (CARP) – A rare acquired dermatosis characterized by brown papules arranged in a reticulated pattern that localizes primarily in the intermammary, epigastric, and interscapular regions. Most commonly affects young adults, particularly women and people with darker skin phototypes. KOH staining is often negative, but CARP is regularly treated with oral minocycline or erythromycin. CARP does not respond to rubbing with isopropyl alcohol.