Case Reports

Incidentally Discovered Ochronosis Explaining Decades of Chronic Pain

Although commonly detected early in life, alkaptonuria, a rare congenital metabolic disorder, can be challenging to diagnosis and treat in older patients.

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References

Alkaptonuria is a rare autosomal recessive disorder uniquely known for causing black, or darkened, urine when left standing due to the renal excretion of excess homogentisic acid (HGA). When this disorder goes undiagnosed, as demonstrated in this case, patients experience its many complications without a unifying explanation. The disorder has 3 clinical stages that occur in a predictable order: clinical silence, clinical ochronosis, and ochronotic arthropathy. These stages lead to multiple musculoskeletal, cardiovascular (CV), and renal complications that can be mitigated with management focused on decreasing homogentisic acid buildup, alleviating symptoms, and close monitoring for these complications.

Case Presentation

A 61-year-old African American male with a medical history of multiple traumatic fractures, right Achilles tendon injury, early-onset multijoint osteoarthritis, chronic low back pain, and recurrent nephrolithiasis presented to the emergency department with sudden onset of sharp left ankle pain while moving furniture. His physical exam revealed a positive Thompson test—lack of foot plantar flexion with calf squeeze—and a subsequent magnetic resonance image (MRI) showed evidence of an acute Achilles tendon rupture.

Given these findings the patient was treated with nonsteroidal anti-inflammatory drugs (NSAIDs) and rest to allow for resolution of swelling and inflammation, followed by elective surgery a month later to repair the ruptured tendon. An operative report following his surgery described “black ends to the area where the Achilles was ruptured…and tendinopathy of the flexor hallucis longus with blackening of the flexor.”

A more in-depth patient history revealed that he underwent multiple invasive and noninvasive interventions for his chronic low back and joint pain with medical management of a prior right Achilles tendon injury. His medical history also included multiple nonspecific diagnoses, such as premature atherosclerosis (diagnosed in his third decade), severe lumbar degenerative disc disease, several tendonopathies and cartilage injuries (Figure 1), pseudogout (following calcium pyrophosphate dehydrate crystals found from a left knee aspirate), and chronic pain syndrome. Along this diagnostic journey, he had several health care providers (HCPs) in rheumatology, orthopedic surgery, pain management, and podiatry who offered a range of symptom management options, including physical therapy, NSAIDs, opioid agonists, tricyclic antidepressants, gabapentin, colchicine, and epidural steroid injections, all of which provided little or no relief of his pain. The patient reported that he told a HCP, “I’ll just live with [the pain].”

At the postsurgery follow-up, the patient reported that he had noticed dark urine and dark spots on his ears in the past. He also recounted that chronic joint pain was common in his family, with both his mother and brother receiving bilateral total knee replacements. Taking into consideration the surgical report and this new history, a urine assessment for HGA was ordered and yielded a diagnosis of alkaptonuria.

He later suffered an acute myocardial infarction leading to an incidental discovery of severe aortic stenosis on echocardiography, requiring coronary stent placements and transcatheter aortic valve replacement, respectively. He reported that with CV interventions and joint replacement surgeries, including bilateral knees and hips, his symptoms and quality of life began to significantly improve. However, he continued to have diffuse chronic joint pain unimproved with any single agent or intervention.

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