Abstract
INTRODUCTION: Atraumatic limb pain is a common presentation to urgent and emergency services. The differential is broad, and misdiagnosis can lead to morbidity and mortality. A diagnosis can frequently be reached by the appropriate use of same-day investigations, and secondary care follow up is rarely needed. This case illustrates an example of a more tortuous diagnostic journey with involvement of several clinical teams and uncertainty persisting until the very end. The culprit is a rare manifestation of a common disease, and modified the authors’ diagnostic thought processes. CASE DESCRIPTION: An otherwise well 27-year-old man with a history of left tibial plateau fracture 13 years prior presented to minor injuries after waking with a large, tender effusion to his left knee. He reported that his knee had given way the previous day. This had been happening intermittently since his historical injury. Septic arthritis was unlikely given the absence of pyrexia, a lack of risk factors, and unremarkable inflammatory markers. His x-ray ruled out a fracture and confirmed a large effusion. A soft tissue injury was felt most likely in the context of his knee having given way, so the patient was issued a knee splint and crutches and discharged with orthopaedic follow-up. In clinic two weeks later a large effusion persisted and the patient was unable to straight leg raise. MRI was organised to assess for meniscal pathology, but instead showed an area of well-demarcated bone erosion to the lateral margin of the patella which had been replaced by a 22x15x12mm mass of indeterminate soft tissue material. Radiological differentials included inflammatory and neoplastic causes, gout, pigmented villonodular synovitis, or a giant cell tumour of the patella. He was referred to the sarcoma MDT who added synovial chondromatosis as a further differential. Core biopsy of the lesion was arranged. Histology demonstrated variably-sized deposits of pale, acellular, crystalline material surrounded by fibrous tissue. There was a florid histiocytic and foreign body giant cell reaction to these deposits. His serum urate was 595µmol/L. A diagnosis of tophaceous gout was made on the basis of these findings, and urate lowering therapy commenced. DISCUSSION: Gout is a common cause of atraumatic arthralgia but is relatively rare in those under the age of 30 with an estimated prevalence of 0.4% [Li 2019]. Gouty tophi are considered a feature of advanced gout and typically emerge after at least 10 years of uncontrolled gout [Rana 2021]. It is unusual for tophi to be the presenting complaint for a patient with gout [Salavastru 2020], and the patella is a rare location for tophi to occur [Clark 2016]. This patient posed a diagnostic challenge due to this very unusual combination of features combined with his previous traumatic history. Urgent care, rheumatology, orthopaedics, sarcoma MDT, radiology, and histopathology teams were all involved in reaching this diagnosis, which reflects the complex structure of the modern medical system. The process of ruling out a life-threatening cause and arriving at a solution proceeded efficiently thanks to effective communication between teams, appropriate referrals, and the availability of expertise. Unfortunately, despite the prescription of urate lowering therapy for over a year the patient’s uric acid has not fallen. Allopurinol dosing has been uptitrated with no effect. We suspect poor concordance with treatment is the most likely cause, which is a challenge particularly prevalent in younger patients [Khalid 2018]. This is of particular concern given the increased cardiovascular risk conferred by an early-onset gout diagnosis [Ferguson 2024]. There is scant reporting in the literature of tophaceous gout as the index presentation of gout, the development of this advanced form of the disease in young patients, and how this should be considered in the management of the long-term health of such patients. The authors would be interested in the thoughts and experiences of CBC attendees regarding these areas. How far would our fellow attendees go in looking for genetic and endocrinological bases for this presentation, for example? KEY LEARNING POINTS: • Gout should be actively considered in the differential diagnosis of atraumatic, or mildly traumatic, joint pain in young adults. • Early-onset gout is associated with increased cardiovascular risk. • Tophi can be the first presenting feature of gout, and can affect the patella. • Tophi can go unnoticed on plain imaging. • Radiologically, gouty tophi can be indistinguishable from several inflammatory and neoplastic conditions. • Biopsy can be necessary to positively identify gouty tophi. • Gout is not always easily diagnosed, and does not necessarily follow a straightforward diagnostic pathway.