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.