A review of world literature reveals several cases that may be similar to FADES. In 1954, Ber7 reported "dirty" brown patches of hyperkeratosis of the elbows and knees, which he named "the sign of dirty knees and elbows," as an early clinical sign of mild hypothyroidism in adults and children. No mention is made of frictional stress in these patients.7 None of the patients we describe with FADES has a history of hypothyroidism. There have been several reports of dermatoses secondary to occupational frictional stress. Wahlberg8 described cases of asymptomatic hyperkeratosis on the dorsal hands and feet of Swedish carpet installers thought to be secondary to friction. Menne and Hjorth9 described cases of red, scaly, vesicular, and pustular dermatoses on the palms and fingertips of workers handling pressure-sensitive carbonless paper in Denmark. The condition typically cured in a few weeks by avoidance of frictional trauma. Menne10 also described a similar dermatitis on the palms of post office workers caused by prolonged rubbing against a rough plastic table. Physicians in Jordan,11 Mexico,12 Iraq,13 Japan,14-16 and Italy17 also described cases of skin darkening that they termed friction melanosis,11,12,14,16,17 friction dermal melanosis (lifa disease),13 and nylon clothes friction dermatoses.15 These patients presented with asymptomatic brownish patches over bony prominences that were associated with long-term rubbing with scrub pads (sedge pads,12 lifas13), clothing,12 nylon towels,14-16 and horsehair gloves.17 Most of these cases, however, occurred predominantly in young thin women and involved the skin overlying the clavicle, vertebra, lateral neck, and upper back. This differs from FADES, which appears to be equally prevalent among men and women, affects young to middle-aged adults of average body weight, and presents with discoloration of the extensor surfaces of the elbows and knees. Most significantly, results of histopathologic examinations in frictional melanosis demonstrate increased melanin deposition within the epidermis and dermal macrophages. Our patients with FADES failed to show evidence of an increase in dermal melanin pigment. This histologic difference might relate to the fact that friction more easily produces PIH in patients with darker skin types in Jordan, Mexico, Iraq, Japan, and Italy. Iwasaki et al18 described a case of biphasic amyloidosis arising from friction melanosis in a Japanese woman with a history of long-term use of nylon towels. The brown asymptomatic hyperpigmentation on the woman's back, characteristic of friction melanosis, became gradually more itchy and associated with several small papules. The results of biopsy specimens taken from both the papular and macular pigmented lesions on her back revealed dermal amyloid deposits. It appears that amyloid deposits are produced by the same frictional stress that causes friction melanosis.18,19 Our patients with FADES showed no evidence of amyloidosis. Acanthosis nigricans involving the elbows, knees, and knuckle pads in patients with diabetes mellitus and obesity rarely has been described.20,21 None of our FADES patients had a history of diabetes mellitus, obesity, or hyperpigmentation involving the neck or axilla, which are commonly involved in acanthosis nigricans. FADES can be distinguished easily from conditions that produce brown discoloration, including lichen simplex chronicus, macular amyloidosis, terra firma-forme dermatosis, PIH, psoriasis, acanthosis nigricans and pseudoacanthosis nigricans, reticular and confluent papillomatosis of Gougerot and Carteaud, and X-linked ichthyosis.22 Patients with lichen simplex chronicus23 and macular amyloidosis24 can be distinguished from patients with FADES because they have severe pruritus, xerosis, history of atopy, and specific distinguishing histopathologic changes. Terra firma-forme dermatosis is not caused by friction but is related to a buildup of dirt and scale in areas that are not scrubbed.25-27 This condition is not found on the extensor surfaces, and the patches rub off with alcohol. PIH is caused by melanin deposition within melanophages in the papillary dermis rather than by the epidermal changes of FADES.28 Psoriasis occurs on extensor surfaces but has thick, white, micaceous scaling and psoriasiform hyperplasia of the epidermis. Acanthosis nigricans and pseudoacanthosis nigricans involve flexural areas rather than the extensor surfaces.29 Reticular and confluent papillomatosis of Gougerot and Carteaud involves the central upper back or chest rather than the extensor surfaces.30 X-linked ichthyosis can be distinguished from FADES because it shows considerable scaling, involves the flexural surfaces of the extremities, occurs in young adulthood, and is restricted to men. We believe FADES is a common condition that easily can be recognized and differentiated from other conditions with skin darkening. A biopsy rarely is required. Treatment with keratolytic agents and avoidance of frictional stress are modestly effective in some cases.