“Shoulder pain and limitation of motion in a young girl: think different”

Synovial chondromatosis is a rare benign condition affecting the synovial membrane, with only a few cases described in pediatric population [1,2,3,4]. It is characterized by intra-articular loose bodies deriving from the subsynovial tissue, in which metaplastic synovial cells form cartilaginous bodies which can even ossify. Traditionally, chondromatosis can be classified as primary, if a previously healthy joint is affected, or secondary, if preceded by a pathological condition. The former is idiopathic and typical of the younger age [5, 6]. The natural history of the disease encompasses three stages: in stage I, an early inflamed synovia is present; stage II is characterized by cartilaginous sessile formation, while in stage III there are calcified loose bodies with minimal synovial inflammation [9].

Symptoms may be aspecific and insidious, as in our case, with a slow worsening of pain, tenderness, decreased range of motion and locking of the affected joint. Nevertheless, in a few cases, it can be asymptomatic and found incidentally. SC usually affects large and weight-bearing joints, mainly the knee or hip, while ankle, shoulder and elbow are extremely rare.

Plain radiographs can address the right diagnosis and multiple intra-articular calcified lesions are pathognomonic, with the typical “rice-grain” pattern, but in 20% of cases standard radiography can be unremarkable, as in our patient. Indeed, Maurice et al. showed that only 54% of nodules in the acute phase of disease were visible on plain radiographs, whereas 88% of transitional phase and 100% of mature phase nodules could be seen on radiographic imaging[7]. For all these reasons, delayed diagnosis and treatment are common. MRI or computed tomography (CT) can identify the typical lesions, even in the early stages. Early MRI findings show multiple hypointense formations in T1-weight sequences, which are hyperintense in T2 for the high water-content of cartilaginous bodies within the articular space, bursae or along the tendon sheaths. A contrast-enhanced synovia characterizes the first stages of the disease. If loose bodies are yet to be ossified, hypointense lesions are present in all the sequences [8].

In children, persistent arthralgia requires an extended work-up. Pediatric long-lasting mono- or oligo-arthralgia should comprise juvenile idiopathic arthritis (JIA) in the differential diagnosis [10]. Oligoarticular JIA typically affects large joints with swelling, pain and limitations of movements. Laboratory exams and plain radiographs may be negative, but the elevation of inflammatory markers and anti-nuclear antibodies (ANA) are typical. Considering 20% of JIA are associated to uveitis, an ophthalmological evaluation can help in the final diagnosis [11]. In our patient, as commonly observed in mechanical pain, symptoms were mainly present during upper arm movements, while inflammatory pain typical of arthritis arises after resting with morning stiffness. Moreover, shoulder involvement is rare in JIA as well as it usually manifests during childhood. Finally, ultrasound may be helpful in JIA diagnosis since it may detect synovial hypertrophy and doppler-power positivity.

Of note, mono-articular involvement with similar insidious pain requires to rule out tubercular arthritis. The slow progression of symptoms is similar, and both can show the “rice-grain” radiological pattern [12, 13]. Lastly, SC belongs to a wide group of neoplastic-like lesions of the articular space. MRI can help distinguish chondromatosis from other benign lesions such as pigmented villo-nodular synovitis or synovial hemangioma [2, 6]. Nevertheless, a differential diagnosis with intra-articular malignancies may be more insidious. For example, chondrosarcoma shares similar radiological findings and histological confirmation is mandatory. The clinical indications to arthroscopy in children are rare, but the presence of an uncommon, unexplained mono-articular arthritis is one of the recommendations.

Pediatricians should be aware of this condition because a prompt diagnosis and treatment can avoid secondary damage to the joint, especially in the puberal and developmental ages. Moreover, retrospective studies from adults described a low risk of developing chondrosarcoma (5% of SC) [14,15,16].

Although in sporadic case reports, conservative management was described, the main treatment remains surgery, removing arthroscopically the loose bodies [2, 4, 17]. Up to now, there is no strong evidence about the role of synovectomy, even if this technique is preferred due to a lower risk of relapses [18], that unfortunately remain frequent. After surgery, the patient should be followed up with MRI for at least two years to rule out recurrence.

In conclusion, this case shows a rare condition of monoarticular pain in children, and pediatricians should keep in mind synovial chondromatosis in the differential diagnosis to avoid delayed diagnosis and treatment. This can be helpful to prevent articular damage and to rule out malignancies.

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