Clinically exogenous ochronosis appears very similar

Clinically, exogenous ochronosis appears very similar to melasma. Other differential diagnoses include bilateral nevus of Ota, Riehl melanosis, acquired bilateral nevus of Ota-like macules, postinflammatory hyperpigmentation, and drug-induced hyperpigmentation, such as minocycline and amiodarone. A skin biopsy is important and suffices to offer a diagnosis. Histologically, yellow-brown, banana-shaped fibers can be observed in the upper dermis of ochronotic lesions. They represent degenerated elastic or collagen fibers with deposits of ochronotic pigment, which can be stained blue-black with methylene blue but not Perls\' or Fontana–Masson stains. Homogenization and swelling of collagen bundles can be observed in early lesions. Sarcoid-like granulomas and the phagocytosis of ochronotic fibers by multinucleated giant cells were reported. Transepidermal and transfollicular elimination of ochronotic fibers have been documented. Ultrastructural examinations show amorphous electron-dense structures that infiltrate collagen bundles or are located within the core of elastic fibers. Dermoscopic features of exogenous ochronosis have been described. It reveals irregular brown-gray globular, annular, and arciform structures throughout the lesion. By contrast, the dermoscopic features of melasma are different and are characterized by a fine brown reticular pattern on a background of a faint light brown structureless area. Therefore, a clinician may use the dermoscope to make a diagnosis; an invasive diagnostic method such as skin biopsy may not be required. Our patient recalled using topical bleaching agents containing 4% of hydroquinone for 4 years prior to the development of the current pigment disorder. The use of topical hydroquinone is the most common cause of exogenous ochronosis. Topical hydroquinone is believed to locally inhibit homogentisic nicergoline oxidase in the skin, resulting in the polymerization of excess homogentisic acid, and ultimately forming ochronotic pigment. In addition, associations with phenol, quinine injections, resorcinol, and oral antimalarial agents have also been indicated. Initially, only the prolonged use of high concentrations of hydroquinone for at least 6 months was thought to cause exogenous ochronosis. However, topical application of 2% hydroquinone for merely 3 months has also been reported to result in the development of this disorder. The treatment of exogenous ochronosis remains challenging, and avoidance of the inducing agent is critical. Applications of topical retinoic acid, trichloroacetic acid, corticosteroids, and cryotherapy are not effective. The efficacy of laser therapy varies. Dermabrasion using a CO laser was reported to yield satisfactory results. Q-switched lasers with the wavelengths absorbed by melanin have been used in the literature with success. For example, a case of exogenous ochronosis treated with a Q-switched ruby laser (694 nm) showed improvement in ochronotic lesions. Bellew and Alster reported that Q-switched Alexandrite 755-nm lasers are effective for treating exogenous ochronosis. By contrast, the effect of intensed pulsed light therapy at 645 nm was unsatisfactory. Regarding the case described in this paper, the results of laser therapy using two modalities (a Q-switched Alexandrite laser at 755 nm and a Q-switched Nd–YAG laser at 1064 nm) showed unwanted results. Our case was the first to use the 1064-nm Nd–YAG laser to treat ochronosis. It showed similar results with the Q-switched Alexandrite laser, both of which were darker than the untreated area. Further investigation is required to establish effective treatments for exogenous ochronosis.
A 14-year-old girl had an asymptomatic lump on her scalp since birth. Over the course of a few months, she noticed some asymptomatic elevations, which slowly grew on the lesion (A). On physical examination, several erythematous papules, not tender to the touch, were found on her right parietal scalp. There was a large, soft plaque with an ill-defined border underneath the papules, and some subcutaneous nodules were palpable in the plaque.