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Differential Diagnosis & Pitfalls

• Terra firma-forme dermatosis (TFFD) – Brown or dirt-like discoloration of the skin that is impervious to normal hygiene but is readily removed by swabbing with isopropyl alcohol pads. A history of long-standing resistance of the discoloration to regular washing or scrubbing is suggestive of TFFD.
• Inherited or acquired ichthyoses (see ichthyosis vulgaris)
• Xerosis
• Acanthosis nigricans – Brown, velvety plaques arising in the body folds, often serving as a marker of hyperinsulinemia secondary to insulin resistance in obese patients.
• Pityriasis versicolor – Superficial mycosis typically presenting in warm and humid environments. Can appear as either hyper- or hypopigmented macules. Potassium hydroxide (KOH) preparation reveals hyphae and spores, commonly referred to as "spaghetti and meatballs."
• Seborrheic keratosis – Nearly ubiquitous in older adults. Initially presents as flat to slightly raised, tan or brown macules that develop a familiar verrucous, "stuck-on" appearance.
• Epidermal nevi – Benign overgrowth of epidermis. Often present at birth or develops during childhood.
• Confluent and reticulated papillomatosis – Presents with brown papules arranged in a reticulated pattern primarily along the intermammary, epigastric, and interscapular regions. More common among young adults, particularly women and individuals with darker skin phototypes.
• Postinflammatory hyperpigmentation – Presents as hyperpigmented macules or patches in the same distribution as the initial inflammatory process. Typically seen after an inflammatory process, this can take months or years to resolve.
• Dermatitis artefacta – Wide range of lesions, from red patches to swellings, scars, crusts, and denuded areas that are self-inflicted by the patient via mechanical or chemical means. Lesions appear in bizarre patterns (eg, geometric or linear) that are clearly demarcated on areas accessible to the patient's hands (eg, on the face, arms, legs). Classically seen in young females who are immature or attention seeking.

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