Ochronosis Workup

Updated: Mar 07, 2017
  • Author: Paul N Skiba; Chief Editor: Dirk M Elston, MD  more...
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Workup

Laboratory Studies

Most laboratory testing for alkaptonuria detects the alterations in the urine. Increased urinary levels of homogentisic acid (HGA) are characteristic of this metabolic disorder.

Elevated levels of HGA in the urine, blood, and other tissues can be determined by specific enzymatic and colorimetric tests, direct spectrophotometric methods, high-performance liquid chromatographic testing, and molecular techniques.

Other simple urinary studies include darkening of urine with the addition of sodium hydroxide, black reaction with FeCl3, and blackening of photographic emulsion paper with alkali added to urine.

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Imaging Studies

In patients with ochronotic arthropathy, radiography and MRI help identify characteristic and diagnostic features, including articular space narrowing up to osseous ankylosis, calcifications, osteophytosis, and reactive sclerosis of the articular surfaces. [13, 19, 20] Bone scintigraphy can be useful in evaluation, correlation with the clinical course, and follow-up of such patients. [21]

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Other Tests

Synovial fluid examination of affected joints shows characteristic frequent pigmented fibrillar connective tissue, which are golden-brown with microscopy, while being black on gross examination. [22]

Arthroscopy can be used in diagnosing cases of ochronotic arthropathy. [23]

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Procedures

Dermoscopy has proved useful in exogenous ochronosis. In addition to melasma findings, dermoscopy reveals amorphous, densely pigmented structures obliterating some follicular openings and multiple thin, short, arciform structures. [24, 25]

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Histologic Findings

Skin biopsy samples with hematoxylin and eosin staining reveal yellowish brown – pigmented bodies in the dermis that represent altered widened elastic fibers, as well as in macrophages, endothelial cells, apocrine glands, and epidermal basement membranes. The deposits do not lose their pigmentation after 3 days in 10% hydrogen peroxide. Furthermore, the ochronotic pigment reacts with all routine stains for melanin. Such deposits can also be seen in cartilage and elastic tissue.

Exogenous ochronosis reveals ochronotic collagen fibers leading to the formation of ochronotic colloid milium. [26] The dermal cell infiltrate is variable but often granulomatous. Transfollicular elimination of these ochronotic fibers has been reported.

Experimental evidence from 2016 has shown the presence of serum amyloid A (SAA) in several alkaptonuric chondrocytes, classifying alkaptonuria as a secondary amyloidosis. SAA in alkaptonuric chondrocytes has been shown to localize to actin, vimentin, and β-tubulin cytoskeletal proteins. [27]

Note the images below.

Upon microscopic examination, amber-colored, oval Upon microscopic examination, amber-colored, oval structures are detected in the mid-to-upper dermal tissues (hematoxylin and eosin, original magnification X40).
Upon higher magnification (of Image 3), ochronosis Upon higher magnification (of Image 3), ochronosis reveals homogenization and swelling of collagen bundles (hematoxylin and eosin, original magnification X100).
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