Discussion
Primary malignant bone tumours arising in the foot are exceedingly uncommon. In the case of Ewing’s sarcoma (ES), the lytic lesions initially present with clinical symptoms such as pain, swelling, and occasionally fever (particularly in the presence of metastatic disease),8 which was seen in our case too. Consequently, a significant number of patients with ES initially receive a misdiagnosis of tendinitis or osteomyelitis and are treated accordingly.9,10 Around 20% of patients exhibit a concomitant history of trauma.11 According to Yang et al.,12 the median duration of delay in reaching the final diagnosis from the onset of symptoms is 52 weeks. In our case, this problem did not manifest. ES typically originates from the diaphysis or meta-diaphyseal region of the long bones and commonly involves the pelvic bones and ribs. Infrequently encountered locations include the cranial bones, scapula, vertebra, as well as the phalanges and metatarsals of the hand and feet.13 Foot involvement in ES is observed in a minority of cases, ranging from 0.93% to 4.2%. When the foot is affected, the most common sites of involvement are the calcaneum (heel bone) and the metatarsals (bones of the midfoot).14,15 However, talus involvement is an exceedingly rare occurrence, with the first case reported by Cohen et al. in 1953.16
Clinical imaging is normally performed when the patient fails to show improvement after receiving antibiotics and/or analgesics. In such cases, initial radiological imaging, performed in two planes, may reveal indications of tumour-related osteolysis and periosteal reactions. The presence of these radiographic findings suggests a potential diagnosis of primary malignant tumour.17 Furthermore, the plain radiographs often exhibit a distinctive pattern known as a ”permeative” or ”moth-eaten” appearance, which indicates a destructive osteolytic lesion. This pattern is most commonly seen in long bones. In the foot and ankle, bone destruction tends to be more prominent than periosteal reactions and may manifest with an atypical presentation that resembles a benign lesion. The classical periosteal reaction referred to as ”onion skin peel” is predominantly observed in tumours affecting the diaphysis.18 Additional radiological imaging is necessary and magnetic resonance imaging (MRI) is employed for detailed assessment. MRI imaging is useful in determining the extent of the tumour and provides precise details regarding its relation to adjacent blood vessels and nerves.17 In modern medical practice, PET/CT has become the predominant investigation for evaluating metastases, enabling the detection of both skeletal and visceral metastatic spread and eliminating the necessity for bone marrow biopsy.19 Common sites of metastasis encompass the lungs, bones, liver, brain, and distant lymph nodes.4In our case, extensive bony and visceral metastases were not seen.
Relying solely on radiologic imaging is inadequate for establishing a definitive diagnosis of ES. Therefore, histopathological confirmation is essential.17 Although the gold standard method for obtaining tumour specimens is an incisional open biopsy, a minimally invasive procedure such as a core needle biopsy yields an adequate quantity of tissue in the majority of cases. Microscopically, the tumour is composed of sheets of small, round blue cells, exhibiting a high nuclear-to-cytoplasmic ratio.13 Supplementary investigations, such as immunohistochemical (IHC) markers and molecular genetics, play a critical role in narrowing the differentials and ultimately leading to a final diagnosis. The CD99, an IHC marker, demonstrates positive expression in over 90% of ES cases. However, it is also observed in various other conditions, including lymphoblastic lymphoma, small-cell osteosarcoma, and mesenchymal chondrosarcoma, among others. Hence, the presence of FLI-1 immunoreactivity in a suspected primary small round cell bone tumour greatly supports the diagnosis of ES.20 Moreover, laboratory findings in cases of ES include elevated erythrocyte sedimentation rate (ESR) and levels of lactate dehydrogenase (LDH), moderate anaemia, or leucocytosis.9
Treatment of ES depends on modern multimodal therapeutic regimens, involving a combination of chemotherapy for systemic control and radiotherapy and surgery for local control.8,9,21 In cases of foot involvement, where there is no evidence of metastasis, amputation is the preferred surgical procedure over limb salvage.12,22 The reason includes poor tumour compartmentalization in the foot, but, in our case, adequate bone resection was achievable and no challenges were encountered during bony and soft tissue reconstruction. Although Ewing’s sarcoma has the worst prognosis amongst all osseous foot malignancies, with the shortest median time to death,12 patients presenting with metastatic ES have notably poorer outcomes and, as a result, are usually managed with a treatment regimen involving chemotherapy and radiation therapy, while avoiding surgical interventions.23 The five-year survival rate for patients with localized disease is significantly higher, at approximately 80%, in contrast to those with bony metastasis, where survival rates range from 30% to 19%.24 Given the favourable prognosis in our case, the tumour board did not recommend a palliative chemotherapy and radiotherapy.