Fig. 1a). Initial tentative clinical diagnoses were TFFD, pityriasis versicolor and extrafacial melasma. Potassium hyroxide examination of skin scrapings was negative. Dermatoscopy showed a 'stone pavement' pattern, consisting of large polygonal brownish scales interrupted by furrows. Examination under Wood light (WL) in a darkened room revealed white fluorescence of the lesions, reminiscent of snow in a clear night (Fig. 1b). A biopsy was not taken, as a 'wipe test' with 70% ethyl alcohol accomplished clearance of the lesions, thus confirming the diagnosis of TFFD (Fig. 2a,b). Clinically, TFFD is characterized by brown-grey, velvety, pigmented patches or plaques, usually on the face, neck, trunk or ankles. 1,2 Occurrence of TFFD at surgical sites has been documented. 3 The mechanism of TFFD is unknown. It has been hypothesized that retention hyperkeratosis (abnormal and delayed keratinization) is the underlying endogenous pathogenetic trigger. Exposure to sunlight and urea-containing emollients have been incriminated as exogenous triggering factors. 1 A relationship between TFFD, xerosis and atopic dermatitis has also been put forward. 1,2 We previously theorized that remnants of soaps, cleansers, emollients, bath oils, ointments or adhesives over genetically susceptible, scaly, dry or eczematous skin may impart to the skin adherent or keratoplastic features that impede adequate exfoliation, thereby resulting in melanin retention and buildup of scales, sweat, dirt and sebum. 1 Skin biopsy is not required for establishing the diagnosis of TFFD. The diagnosis may be supported by dermoscopy, which shows a 'stone pavement' pattern of scales and furrows in a mosaic, cobblestone or tile-like pattern, and confirmed by forceful rubbing with a gauze pad immersed in 70% isopropyl alcohol or ethyl alcohol. 1,2 This noninvasive and rapid diagnostic test, termed SMART (Skin Modified by Alcohol Rubbing Test), prevents unnecessary laboratory investigations or skin biopsy. 4 In dermatology, WL is principally utilized for the diagnosis of fungal and bacterial infections, pigmentation disorders and porphyrias. 5 Clinically TFFD is characterized by hyperpigmented lesions; however, WL paradoxically excited chalk-white fluorescence in the present case. This technique helped us to exclude pityriasis versicolor, acanthosis nigricans, confluent and reticulated papillomatosis, ashy dermatosis and extrafacial melasma. Contrary to the positive results for WL examination in the present case, some published previous reports documented negative WL results in TFFD. 6 The main reason(s) for white fluorescence of TFFD under WL and its diagnostic and differential utility in TFFD requires elucidation. Previously, keratin reflectance was incriminatedas the source of white fluorescence under WL in some keratinization disorders. 5 Routine and meticulous use of WL in TFFD cases is required to collect cases with similar observations.
