Alkaptonuria (Black Urine Disease) Clinical Presentation

Updated: Mar 18, 2021
  • Author: Karl S Roth, MD; Chief Editor: Maria Descartes, MD  more...
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Presentation

History

Because alkaptonuria is usually autosomal recessive, a family pedigree, in all likelihood, reveals no other affected individuals. However, because many genetically affected individuals are asymptomatic, the low frequency of clinically affected family members may be due to a lack of ascertainment.

Despite the intrinsic biochemical defect and the expectation that all affected individuals should excrete urine that becomes black when left standing, a significant number of people with alkaptonuria do not present with this clinical finding.

The most common history is one of arthritic symptoms confined chiefly to the spine, hips, and knees. Virtually all people with alkaptonuria eventually experience arthritis. Onset of thoracic back pain, lumbar back pain, or both around age 30 years is frequent.

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Physical

Slate blue or gray discoloration may be found in the sclerae or ear cartilage.

Calcifications may be palpable in the discolored areas, particularly in the cartilage of the ear.

Joint mobility diminishes, as in osteoarthritis. Ankylosis may be present. Spontaneous fusion of one or more discs may occur, with consequent diminished spinal flexion. Joint effusions, particularly in the knee are common and range of motion may be significantly diminished.

Signs of aortic or mitral valvulitis may be present.

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Causes

Inability to convert homogentisic acid to maleylacetoacetic acid results in accumulation of the former. Homogentisic acid is subsequently converted to benzoquinone acetic acid and spontaneously polymerized. Deposition of the polymer in association with cartilage is the initiating pathophysiologic cause of the arthritis. [25]

Although unproven, the deposition of polymer is assumed to also cause an inflammatory response that results in calcium deposition in affected joints.

Exogenous agents including quinacrine (Atabrine), carbolic acid, and hydroquinone have been reported to cause an ochronotic picture without the joint disease. All have been reversible.

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