Skin-nontumor / Clinical Dermatology
Reviewer: Mowafak Hamodat, MB.CH.B, MSc., FRCPC (see Reviewers page)
Revised: 5 September 2011, last major update August 2011
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.
● Autosomal recessive disorder of increased urinary excretion of homogentisic acid (alkaptonuria), with deposition of “ochre-colored” pigment in collagen-rich regions (ochre: moderate orange-yellow)
● Occurs in 50% with alkaptonuria
● Due to disorder of homogentisic acid oxidase gene on #3q, intermediate component in metabolism of tyrosine and phenylalanine, causing accumulation of benzoquinone acetic acid, which binds to collagen irreversibly
● Clinically black pigmentation of joints (arthritis with pigment deposition in cartilage and intervertebral disks), cardiovascular system (valvular calcifications and stenosis), kidney (black urine, pigmented stones) and skin (cutaneous pigmentation)
● Also involvement of sclera of eye
● Pigment in dura matter of brain (Arch Pathol Lab Med 2001;125:961), ochronotic arthropathy
● Yellow–brown sharply defined irregularly shaped and frequently fragmented fibers in superficial dermis
● Ochronotic pigment is autofluorescent, appears black with methylene blue, but does not stain with Van Gieson or Pearl’s stain or the Masson Fontana reaction
● Pigment granules often present in epithelium and basement membrane of sweat glands, in endothelium and within dermal macrophages
● Hydroquinone induced ochronosis shows melanophages in upper dermis associated with depigmentaion of the epidermal melanocytes
● In early lesions, collagen fibers appear basophilic and swollen before developing characterstic yellow ochronotic morphology
● With chronicity, large amorphous eosinophilic granules may develop resembling colloid milium
● Solar elastosis and foregn body granuloma are common features
● Pigmentation secondary to antimalarial drugs is due to melanin and hemosiderin deposition in addition to the classic ochronotic fibers
End of Skin-nontumor / Clinical Dermatology > Other dermatoses > Ochronosis
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