Abstract
Introduction
Crowned dens syndrome (CDS) is an under-recognised presentation of calcium pyrophosphate deposition disease (CPPD), typically affecting the elderly and presenting with acute or subacute neck pain and stiffness. Periodontoid pseudotumour formation—more commonly associated with rheumatoid arthritis or mechanical instability—may occasionally result from crystal arthropathy, particularly CPPD. These cases can mimic inflammatory or degenerative conditions, often leading to neurosurgical referrals and extensive investigation. This case highlights an atypical and slowly progressive presentation of axial CPPD, with radiological evidence of periodontoid erosions and chondrocalcinosis. It underscores the importance of considering crystal arthropathy in the differential diagnosis of cervical spine pathology.
Case description
A 70-year-old man with a background of hypertension, osteoarthritis, and bilateral hip replacements presented with a four-month history of progressive neck and right shoulder pain. A retired teacher with a previous smoking history and moderate alcohol intake, he was initially referred to orthopaedics for possible surgical intervention. An initial cervical spine MRI revealed multilevel degenerative disc disease without significant stenosis. Due to ongoing symptoms, a CT scan was arranged, which revealed well-demarcated punched-out erosions with sclerotic margins involving the odontoid process, alongside surrounding calcification. The case was discussed in the neurosurgical MDT, which recommended rheumatology input in view of suspected inflammatory or crystal arthropathy. The patient reported worsening neck pain with minimal movement, as well as intermittent paraesthesia in both upper limbs. There was no reported weakness or lower limb involvement. On clinical examination, he had markedly reduced cervical range of motion in all planes, particularly right lateral rotation and flexion. There was no evidence of peripheral joint swelling or features suggestive of active rheumatoid arthritis or acute gout. Blood tests showed elevated inflammatory markers with ESR 42 mm/hr and CRP 23 mg/L, but serum urate was within normal limits. Rheumatoid factor, anti-CCP antibodies, and ANA were negative. X-ray of hands revealed severe erosive osteoarthritis of the DIP and PIP joints, with chondrocalcinosis in both wrists and the right knee. A diagnosis of CPPD-related retro-odontoid pseudotumour (crowned dens syndrome) was made. He was commenced on etoricoxib and short courses of colchicine for symptom control. Due to the chronicity and stability of his symptoms, and the absence of neurological deficit, surgical decompression was deemed unnecessary. He remains under rheumatology follow-up with conservative management and monitoring for any progression in neurological or structural compromise.
Discussion
This case exemplifies the diagnostic complexity of axial crystal arthropathy, particularly when radiological findings mimic inflammatory or degenerative pathology. Crowned dens syndrome is characterised by calcific deposition in the ligaments surrounding the odontoid process, most commonly due to CPPD. It can present acutely, with fever and neck stiffness, or more insidiously as in this case, with chronic pain and paraesthesia. Retro-odontoid pseudotumours are typically described in association with rheumatoid arthritis and atlantoaxial instability, but they have increasingly been recognised in association with CPPD, particularly in elderly patients with cervical degenerative disease. According to EULAR and BSR guidelines, CPPD diagnosis is supported by radiological evidence of chondrocalcinosis and clinical features consistent with acute or chronic arthritis. While the ACR classification criteria for crystal arthropathies primarily address peripheral joint involvement, this case highlights the need to expand clinical suspicion to include axial disease, especially in older patients with atypical presentations. CT imaging was crucial in identifying periodontoid erosions and calcifications, which were not apparent on MRI. EULAR guidance also emphasises CT as the imaging modality of choice for diagnosing crowned dens syndrome. In terms of treatment, the decision to avoid surgery was based on the chronic nature of symptoms, absence of spinal cord compression, and stable neurological status. Conservative management with NSAIDs and colchicine, both recommended first-line therapies in acute CPPD flares, was favoured. Steroids may also be used, though were not required in this case due to adequate symptom control with colchicine and etoricoxib. This case raises key questions around the long-term monitoring of axial CPPD, and whether early detection of periodontoid calcification could prevent irreversible damage. It also highlights the need for improved awareness among orthopaedic and neurosurgical teams regarding crystal arthropathy, to avoid unnecessary surgical interventions in stable cases.
Key learning points
This case highlights several key learning points regarding the presentation, diagnosis, and management of axial CPPD. Firstly, crowned dens syndrome may present in a chronic and indolent fashion, rather than the classical acute febrile neck pain seen in earlier case reports. This makes clinical suspicion more difficult and often results in diagnostic delay, especially when standard imaging modalities such as MRI fail to detect characteristic calcifications. As demonstrated here, CT imaging is essential in assessing the craniovertebral junction, especially in the context of unexplained cervical erosions and surrounding soft tissue masses.
Secondly, retro-odontoid pseudotumours should not be assumed to represent rheumatoid pannus or neoplastic lesions without a full rheumatological workup. In this patient, the absence of serological markers, lack of synovitis, and co-existing chondrocalcinosis strongly supported a diagnosis of CPPD. The erosive changes seen on CT, though concerning, were likely a result of chronic crystal-mediated inflammation rather than aggressive destructive arthropathy.
From a therapeutic standpoint, management decisions in axial CPPD must be carefully individualised. Surgical intervention should be reserved for patients with progressive neurological impairment, spinal instability, or intractable pain. In this case, conservative treatment using etoricoxib and colchicine achieved sufficient symptom control without the need for invasive measures. This reflects current BSR/EULAR guidance recommending NSAIDs and colchicine as first-line therapy in acute or chronic CPPD, with steroids reserved for refractory cases or those with contraindications.
For future clinical practice, this case reinforces the need for heightened awareness of atypical crystal arthritis presentations and the utility of CT scanning in diagnosing crowned dens syndrome. At the conference, I hope to further explore the natural history of axial CPPD, strategies for monitoring retro-odontoid pseudotumours, and when to involve surgical teams in management. It would also be valuable to discuss evolving imaging criteria that better capture axial manifestations of crystal arthropathies.