[Long-standing myalgia and hypouricemia in a young woman : Case report and review of the literature].

A 46-year-old female patient had been suffering from multiple symptoms such as arthralgia, myalgia, general fatigue, exhaustion, concentration problems, forgetfulness, difficulty falling asleep and sleeping through the night and depression since the age of 27 years old. Rheumatological preliminary findings revealed rheumatoid arthritis with a lack of response to basic treatment as well as secondary fibromyalgia. Supplementary metabolic examinations were carried out in the case of laboratory tests for hypouricemia, which showed massively increased xanthine levels in the urine. With normal renal function and unremarkable urine sediment, small concrements were sonographically visualized in the renal pelvic calyceal system on both sides. The diagnosis of xanthinuria was made. This is a rare hereditary disorder of purine metabolism with a lack of conversion of hypoxanthine via xanthine to uric acid via the enzyme xanthine oxidoreductase. Clinical courses range from asymptomatic to symptomatic urolithiasis with increased renal xanthine excretion and myalgia with intramuscular xanthine deposits. In addition, non-specific arthralgia and progressive renal insufficiency are described during the course of the disease. Clinically, the overlapping symptoms of fibromyalgia and xanthinuria make it impossible to reliably differentiate between the two entities.