Ewing's sarcoma of the ilium mimicking sacroiliitis

A. Al-Adsani, M. N. Niazy and M. Mohd

Medical Department, Al-Sabah Hospital, Kuwait

Correspondence to: A. Al-Adsani, PO Box 31098, 90801 Sulaibikhat, Kuwait.

SIR, Ewing's sarcoma (ES) is a highly malignant tumour of bone and soft tissues in children and adolescents. The clinical symptoms and signs, as well as the radiological findings, are non-specific, and can be confused with benign disorders. In this communication, we report the case of a 24-yr-old male who presented with a 3 month history of low backache and right sacroiliac joint pain. He was treated with non-steroidal anti-inflammatory drug with little relief. The positive physical signs were fever, restricted range of movement at the right sacroiliac joint and wasting of the right quadriceps muscles. Plain radiograph of the lumbosacral spine revealed significant sclerosis with marginal erosion and loss of the right sacroiliac joint space consistent with sacroiliitis (Fig. 1Go). The left sacroiliac joint was normal. Laboratory investigations revealed normal leucocytes, mild hypochromic anaemia, high erythrocyte sedimentation rate (112 mm/h) and elevated levels of liver enzymes. HLA-B27 was negative. Bone scan revealed multiple areas of increased photon uptake in the skull, ribs, pelvis, humeri and femora. Bone marrow biopsy showed a malignant round cell tumour. Contrast-enhanced CT of the abdomen and pelvis revealed a permeative lesion of the right ilium with periosteal reaction and associated soft-tissue mass extending on either side of the iliac bone, and involving adjacent muscles. The right sacroiliac joint and the right paraspinal muscle were secondarily involved. The liver, spleen, pancreas, kidneys and biliary system were all normal. Open biopsy and immunohistochemistry studies confirmed the final diagnosis of ES with multifocal bone marrow involvement. He was treated with multi-drug chemotherapy.



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FIG. 1.  Anteroposterior radiograph of the lumbar spine and pelvis. The left sacroiliac joint is normal. The right sacroiliac joint shows sclerosis of the ilium, marginal erosions and loss of the joint space (arrow), appearances that are consistent with sacroiliitis.

 
Ewing's sarcoma is the second most common malignant tumour of bone in children and adolescents after osteogenic sarcoma [1]. It is a rare, highly malignant, small round cell tumour of bone and soft tissues. Ninety per cent of the patients are <30 yr old [2]. The aetiology is unknown. However, in 85% of ES, the pathognomonic t(11:22) chromosomal translocation is found. Clinically, the most common presenting symptom is pain (90%), followed by swelling (70%) [3]. It may also present with systemic manifestations such as fever, weight loss and increased sedimentation rate which are commonly associated with metastases [1]. ES can affect almost any bone and soft tissue in the body, but the commonest sites affected are the femur (23%), followed by the pelvis (17%). Delay in the diagnosis is not uncommon. This is attributed to the non-specific symptoms, gradual development of the tumour, the deep location in cases of pelvic tumours and the diagnostic confusion with osteomyelitis [1, 2]. Radiologically, it was classically described as a central, diaphyseal, lytic tumour, which is often permeative and has a lamellated or `onion skin' periosteal reaction affecting a long bone, and associated with soft-tissue mass. The bone lesions are usually lytic, but may be sclerotic or mixed. Most of the lesions are diaphyseal or metadiaphyseal. This classic description is no longer valid. In an analysis of the plain radiographic appearance of ES of bone, the classic description has only 5% sensitivity, but 99% specificity, and 20% prevalence [4]. ES may be misdiagnosed as benign disorders. As far as we are aware, two cases of ES of the ilium mimicking sacroiliitis have been reported [5, 6]. ES of the tibia may mimic osteomyelitis [7]. ES may present as monoarthritis [8], spondylolisthesis [9] and as postpartum back pain [10]. The plain radiographic abnormalities of ES are, therefore, not specific and could mimic benign disorders. CT is helpful in defining the tumour of ES by showing the pattern of bone destruction and the associated soft-tissue mass [5]. MRI is more sensitive than CT in showing soft-tissue involvement and bone marrow metastases [6]. Definitive diagnosis is by an open biopsy and histological examination combined with immunochemistry and cytogenetics. Treatment of ES consists of multi-drug chemotherapy combined with surgery and/or radiotherapy. If the tumour is resectable and the function after resection is predicted to be reasonable, surgery is preferred rather than radiotherapy. The 5 yr survival rate for patients presenting without metastases is 50–75% [1, 6]. In the presence of metastasis, the 2 yr survival is 39% [6]. Prognosis depends on the site and the size of the tumour, presence of metastasis, and the response to chemotherapy. Prognosis is worse if the primary tumour is in the pelvis and the sacrum, and if the tumour is larger than 8–10 cm. In conclusion, ES is a highly malignant tumour of bone and soft tissues in children and adolescents, which can be confused clinically and radiologically with inflammation or infection because of the non-specific clinical manifestations and radiographic abnormalities. It may be misinterpreted as unilateral sacroiliitis if it affects the ilium. Rheumatologists, other clinicians and radiologists should be alert to this rare atypical occurrence.

Acknowledgments

The authors thank Dr Issam Al-Shirbeeni, consultant physician, and Dr Mohammed H. Dahniya, consultant radiologist, of Al-Sabah Hospital for their cooperation in the work-up of this case.

References

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Accepted 25 January 1999





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