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Swelling of a metacarpophalangeal joint

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Q1: What does the radiograph show?

Radiograph shows multiple rounded areas of calcification over the head of third metacarpal and erosion of the head of the metacarpal.

Q2: What is the differential diagnosis?

The most likely diagnosis on the basis of history, clinical examination, and radiographic appearance is synovial osteochondromatosis. The other possible differential diagnoses are listed in box 1.

Box 1: Differential diagnoses

  • Rheumatoid arthritis

  • Chronic infection (including tuberculosis)

  • Trauma: osteochondral fracture

  • Osteochondritis dissecans

  • Osteoarthritis

  • Neuropathic arthritis

  • Gout

Q3: How would you treat this condition?

Treatment usually involves removal of the osteocartilaginous nodules with excision of the involved synovium.

Discussion

Synovial chondromatosis is an uncommon pathological condition which mostly involves the synovium of a large joint and rarely occurs in the hand. However a few cases affecting small joints of the hand have been reported in the literature.1-4 Pathologically it arises from metaplasia of the synovium of the joint and rarely the tendon sheaths. It has been postulated that the multipotential synovioblasts under unknown conditions undergo multifocal metaplasia to form chondroblasts leading to formation of cartilaginous nodules. These nodules can later undergo secondary ossification.5 6

The clinical diagnosis of synovial chondromatosis can be difficult because of non-specific signs and symptoms and rarity of the condition. This disease should be considered in the differential diagnosis of a swollen and painful joint. The common presenting symptoms are pain, swelling, and stiffness of the joint. Physical examination may show tenderness, effusion, and palpable nodules. The radiographic appearance depends upon the extent of ossification of the cartilaginous nodules. In the absence of such ossification the radiograph may show no abnormality and preoperative diagnosis may be difficult. When the lesion occurs with in the capsule of a small joint which has only limited capacity for expansion, secondary erosion of the bone can be seen. In this situation synovial chondrosarcoma should be ruled out on histological examination.

Histological examination shows multiple cartilaginous masses beneath the synovium. These cartilaginous masses may separate from the synovium to form loose bodies. If the cartilaginous masses undergo ossification the condition is termed as synovial osteochondromatosis. The synovial origin of these cartilaginous masses should be emphasised to differentiate this condition from others. As histopathology often shows an increased cellularity and nuclear atypia it is essential to avoid an erroneous diagnosis of chondrosarcoma which requires a totally different management.1 5

The natural history of the disease is of slow progression and may be self limiting6 but if untreated for a long duration, it can lead to an extensive destruction of adjacent bony structures.1 Malignant transformation, though reported,7 is uncommon. Although a case of spontaneous regression of the disease involving the knee joint has been reported,8 the treatment usually involves removal of the cartilaginous nodules with en bloc excision of the involved synovium.

Progress

The swelling was excised under general anaesthesia. There was a loosely encapsulated mass of immature cartilage arising from the dorsum of the metacarpophalangeal joint under the extensor hood. The histopathology was reported as synovial tissue together with fragments of varying sizes containing lobulated hyaline chondroid tissue with no features of malignancy (fig 1 below). The patient remains aymptomatic after three years of follow up.

Figure 1

Photograph of the histology of the lesion showing lobulated hyaline chondroid tissue (haematoxylin and eosin; upper magnification × 20, lower magnification × 160).

Final diagnosis

Intra-articular synovial osteochondromatosis.

References

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