AlcaptonuriaDz

Synonyms: Ochronosis.

ICD-9 Code: 270.2.
ICD-10 Code: E70.2

Definition: This rare metabolic disorder is caused by a deficiency of the enzyme homogentisic acid oxidase and the accumulation of homogentisic acid that binds to collagen, resulting in darkened pigment deposition in cartilage, intervertebral discs, and skin.

Demographics: The disorder is transmitted as an autosomal recessive gene; heterozygotes do not have ochronosis. The incidence of homozygotes is estimated to be one in 200,000.

Cardinal Findings: Skin changes are usually first noted after age 20 years. The delayed onset of skin and cartilaginous changes leaves many undiagnosed until they are elderly, when the clinical findings are striking. The dark pigmentation may be seen in the pinna and external canal of the ear or in skin overlying the nasal and malar areas of the face. Pigmentation is often described as slate blue, gray, or coal colored. This pigment may even appear in axillary sweat and stain clothing. Articular manifestations usually begin in the spine. Peripheral joint pain and subsequent OA may affect the knees, shoulders, and hips. Hands, feet, elbows, and ankles are usually spared.

Diagnostic Tests: The diagnosis is confirmed by demonstrating homogentisic aciduria. Urine samples may be dark colored or become dark if left to stand. Nearly 50% of patients develop a noninflammatory, yellow- or amber-colored synovial effusion.

Imaging: Spinal radiographs show a characteristic pattern of densely calcified intervertebral discs with intervening osteoporotic vertebral bodies, giving the appearance of a “rugger jersey” spine. Degenerative changes or chondrocalcinosis may occur in peripheral joints.

Therapy: Definitive medical therapies are not available; although a low protein diet and ascorbic acid have been advocated. Treatment of the arthritis is symptomatic.

BIBLIOGRAPHY

Schumacher HR, Holdsworth DE. Ochronotic arthropathy. I. Clinicopathologic studies. Semin Arthritis Rheum 1977;6:207–246. PMID:835021