Spontaneous Achilles tendon rupture in alkaptonuria

Alkaptonuria (AKU) is a rare inborn metabolic disease characterized by accumulation of homogentisic acid (HGA). Excretion of HGA in urine causes darkening of urine and its deposition in connective tissues causes dark pigmentation (ochronosis), early degeneration of articular cartilage, weakening of the tendons, and subsequent rupture. In this case report, we present a rare case of a patient presented with unilateral spontaneous rupture of Achilles tendon due to AKU. The patient developed most of the orthopedic manifestations of the disease earlier than typical presentations. Alkaptonuria patients should avoid strenuous exercises and foot straining especially in patients developing early orthopedic manifestations.Alkaptonuria (AKU) is a rare genetic metabolic disorder with an incidence of 1:250,000 in most populations. It is due to deficiency of homogentisate 1,2-dioxygenase (HGD), which is an enzyme involved in the phenylalanine and tyrosine degradation pathway.1,2 Homogentisate 1,2-dioxygenase deficiency results in accumulation of homogentisic acid (HGA), which is oxidized to benzoquinones that polymerize and form a dark pigment. The excess HGA binds to the connective tissues and cartilage. Ochronotic osteoarthropathy is used to refer to the musculoskeletal manifestation of AKU. Ochronosis is the darkening of connective tissues due to the deposition of HGA and/or its polymer in connective tissue. Over time this causes ochronotic osteoarthropathy.3 On microscopic examination yellowish (ocher-like) discoloration of the tissue is seen, but macroscopically the affected tissues appear bluish grey. This leads to weakness and early degeneration of articular cartilage and arthritis.2 Large quantities of HGA excreted in urine causes urine to darken upon standing due to oxidation or after exposure to alkaline agents.1 Rupture of Achilles tendon is an important clinical manifestation of AKU. There are few reports in the literature of spontaneous rupture of the Achilles tendon caused by AKU.4-6 We report a case of an AKU patient presented with a unilateral spontaneous rupture of Achilles tendon. The objective of this case report is to highlight the rare Achilles tendon rupture due to AKU, which can be a reference for physicians and surgeons in the prevention and/or delay of such a complication.