Ochronosis
Updates to Article Attributes
Ochronosis (or, or alkaptonuria), is a rare multisystem autosomal recessive metabolic disorder.
On imaging, the most particular presentation is on the spine, with osteoporotic bones and dense disc calcifications.
Terminology
The term ochronosis usually refers to the bluish black discoloration of certain tissues, such as the ear cartilage and the ocular tissue, seen with alkaptonuria. Some authorities, however, refer to musculoskeletal manifestations of alkaptonuria as ochronosis 3.
Epidemiology
The estimated incidence is around 1:250,000-1,000,000 3,5
Clinical presentation
Patients often have pigmentation of auricular cartilages and sclera. Urine colour tends to be dark (at birth sometimes diagnosed by discolouration of diapers). Up to 25% of patients with alkaptonuria do not have the characteristic dark urine staining,; many patients remain undiagnosed until adulthood.
Pathology
The condition results due to excessive build up-up of homogentisic acid (HGA) from a lack of homogentisic oxidase (a defect in the biochemical pathway for the degradation of phenylalanine and tyrosine). The excess homogentisic acid (HGA) binds to collagen in connective tissue. The affected connective tissues become weak and brittle with time, leading to chronic inflammation, degeneration, and osteoarthrosis (progressive arthropathy).
Genetics
A defective gene has been mapped to chromosome 3q21–q23 5.
Radiographic features
Plain radiograph
The most well described-described features are those involving the skeletal system.
Vertebral
- severe osteoporosis
- multilevel intervertebral disc calcification: tends to be widespread (and involves nucleus pulposus)
-
syndesmophyticsyndesmophyte formation - multilevel disc space narrowing
Joints
- symmetrical or asymmetrical joint space loss: early osteoarthritis
- subchondral sclerosis
- chondrocalcinosis
Complications
- aortic stenosis 4
- spontaneous tendon ruptures have been reported 3
History and etymology
Ochronosis was defined by Virchow, who histologically described the connective tissue in alkaptonuria, given the cartilage's ochre (yellow) hue under the microscope.
Differential diagnosis
For skeletal radiographic manifestations consider
-
calcium pyrophosphate deposition disease (CPPD):
particularly extravertebralmainly extra vertebrae
There is a broad differential for intervertebral disc calcification.
See also
-<p><strong>Ochronosis</strong> (or <strong>alkaptonuria</strong>) is a rare multisystem autosomal recessive metabolic disorder.</p><h4>Terminology</h4><p>The term ochronosis usually refers to the bluish black discoloration of certain tissues, such as the ear cartilage and the ocular tissue, seen with alkaptonuria. Some authorities however refer to musculoskeletal manifestations of alkaptonuria as ochronosis <sup>3</sup>.</p><h4>Epidemiology</h4><p>The estimated incidence is around 1:250,000-1,000,000 <sup>3,5</sup></p><h4>Clinical presentation</h4><p>Patients often have pigmentation of auricular cartilages and sclera. Urine colour tends to be dark (at birth sometimes diagnosed by discolouration of diapers). Up to 25% of patients with alkaptonuria do not have the characteristic dark urine staining, many patients remain undiagnosed until adulthood.</p><h4>Pathology</h4><p>The condition results due to excessive build up of homogentisic acid (HGA) from a lack of homogentisic oxidase (a defect in the biochemical pathway for the degradation of phenylalanine and tyrosine). The excess homogentisic acid (HGA) binds to collagen in connective tissue. The affected connective tissues become weak and brittle with time, leading to chronic inflammation, degeneration, and osteoarthrosis (progressive arthropathy). </p><h5>Genetics</h5><p> A defective gene has been mapped to chromosome 3q21–q23 <sup>5</sup>.</p><h4>Radiographic features</h4><h5>Plain radiograph</h5><p>The most well described features are those involving the skeletal system. </p><h6>Vertebral</h6><ul>- +<p><strong>Ochronosis</strong>, or <strong>alkaptonuria</strong>, is a rare multisystem autosomal recessive metabolic disorder.</p><p>On imaging, the most particular presentation is on the spine, with osteoporotic bones and dense disc calcifications. </p><h4>Terminology</h4><p>The term ochronosis usually refers to the bluish black discoloration of certain tissues, such as the ear cartilage and the ocular tissue, seen with alkaptonuria. Some authorities, however, refer to musculoskeletal manifestations of alkaptonuria as ochronosis <sup>3</sup>.</p><h4>Epidemiology</h4><p>The estimated incidence is around 1:250,000-1,000,000 <sup>3,5</sup></p><h4>Clinical presentation</h4><p>Patients often have pigmentation of auricular cartilages and sclera. Urine colour tends to be dark (at birth sometimes diagnosed by discolouration of diapers). Up to 25% of patients with alkaptonuria do not have the characteristic dark urine staining; many patients remain undiagnosed until adulthood.</p><h4>Pathology</h4><p>The condition results due to excessive build-up of homogentisic acid (HGA) from a lack of homogentisic oxidase (a defect in the biochemical pathway for the degradation of phenylalanine and tyrosine). The excess homogentisic acid (HGA) binds to collagen in connective tissue. The affected connective tissues become weak and brittle with time, leading to chronic inflammation, degeneration, and osteoarthrosis (progressive arthropathy). </p><h5>Genetics</h5><p> A defective gene has been mapped to chromosome 3q21–q23 <sup>5</sup>.</p><h4>Radiographic features</h4><h5>Plain radiograph</h5><p>The most well-described features are those involving the skeletal system. </p><h6>Vertebral</h6><ul>
-<li>syndesmophytic formation</li>- +<li>syndesmophyte formation</li>
-</ul><h4>History and etymology</h4><p>Ochronosis was defined by <strong>Virchow</strong> who histologically described the connective tissue in alkaptonuria, given the cartilage's ochre (yellow) hue under the microscope.</p><h4>Differential diagnosis</h4><p>For skeletal radiographic manifestations consider</p><ul><li>-<a href="/articles/calcium-pyrophosphate-dihydrate-deposition-disease">calcium pyrophosphate deposition disease (CPPD)</a>: particularly extravertebral</li></ul><p>There is a broad differential for <a href="/articles/intervertebral-disc-calcification">intervertebral disc calcification</a>.</p><h4>See also</h4><ul><li><a href="/articles/polyarticular-arthropathy">polyarticular arthropathy</a></li></ul>- +</ul><h4>History and etymology</h4><p>Ochronosis was defined by <strong>Virchow</strong>, who histologically described the connective tissue in alkaptonuria, given the cartilage's ochre (yellow) hue under the microscope.</p><h4>Differential diagnosis</h4><p>For skeletal radiographic manifestations consider</p><ul><li>
- +<a href="/articles/calcium-pyrophosphate-dihydrate-deposition-disease">calcium pyrophosphate deposition disease (CPPD)</a>: mainly extra vertebrae</li></ul><p>There is a broad differential for <a href="/articles/intervertebral-disc-calcification">intervertebral disc calcification</a>.</p><h4>See also</h4><ul><li><a href="/articles/polyarticular-arthropathy">polyarticular arthropathy</a></li></ul>
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