Whole body bone scintigraphy in osseous hydatosis: a case report

Hydatid disease is common in many parts of the world, and causes considerable health and economic loss. This disease may develop in almost any part of the body. Bone involvement is often asymptomatic, and its diagnosis is primarily based on radiographic findings. A whole body bone scan is able to show the extent and distribution of lesions. We describe an unusual case of multifocal skeletal hydatosis and also explain the clinical and diagnostic points. We hope to stimulate a high index of suspicion among clinicians to facilitate early diagnosis and to consider this disease as a differential diagnosis in cases of multiple abnormal activity in bone scintigraphy especially among people in endemic areas.


Background
Echinococcosis is a zoonotic infection caused by adult or larval (metacestode) stages of cestodes belonging to the genus Echinococcus and the family Taeniidae. The adult Echinococcus lives in the small intestine of carnivores such as dogs, wolves, jackals and the excreted eggs of the worm are scattered through the stool of these animals (Schantz, 1991;Thompson, 1995). Echinococcus granulosus has a worldwide geographic distribution and occurs in all continents including circumpolar, temperate, subtropical and tropical zones [1]. The highest prevalence of the parasite is found in parts of Eurasia, Africa, Australia and South America (Figure 1). Within endemic zones, the prevalence of the parasite varies from sporadic to high, but only a few countries can be regarded as being free of E. granulosus ( Figure 1).
Bone localization is also rare comprising 0.5% to 2.5% of all human hydatidosis [3]. The diagnosis of osseous hydatidosis is primarily based on radiological findings. Treatment is difficult and recurrence is common [4]. Therefore, plain radiography, CT scan, and MR imaging are helpful in diagnosing skeletal cystic echinococcosis [5]. Osseous foci may manifest as bone pain and deformity, particularly among patients in the 30-60 year olds age group [6,7]. Hereby, we present an unusual case of multifocal skeletal hydatosis and also explain the clinical and diagnostic points to facilitate early diagnosis of this condition.

Case presentation
The patient was a 53 year old man with a history of osseous hydatosis since the age of 30. He had had three surgical operations due to the disease. He had low back pain and radicular pain in both legs which had been aggravated over the past month. His past history for any other illnesses was negative. There wasn't a history of coughing or other respiratory symptoms. His general condition was good. On examination we detected low back tenderness in the lumbar area. He had a painful tumor-like mass in the right hemipelvis which was slightly warm without overlying erythema. Straight leg raising test (SLR) was positive in both legs. He had motor and sensory deficit, muscular atrophy and gate disturbance. No other abnormal findings were detected. Simple x-ray of the right femur showed advanced lytic bone destruction, centered in the proximal two thirds of the right femur. In addition there were the appearances of nailing due to previous surgery ( fig. 2). The plain pelvic xray also revealed marked lytic and sclerotic lesions involving the right hemipelvis ( Figure 3). A whole body bone scintigram revealed multiple foci of increased radiotracer uptake in the lower lumbar spine, left sacroiliac region and right knee. In addition, there was soft tissue bulging in the right hemipelvis as well as a displaced and disconfigured right femur (Figure 4). Chest x ray was normal.

Conclusion
Hydatidosis is a common disease of both humans and animals resulting from infection with the larval stage of the Echinococcus granulosus tapeworm. This disease is common in many parts of the world and causes considerable health and economic loss [8].
Liver and lungs are the most commonly involved organs and involvement of bone and muscles is uncommon [9]. The prevalence of bone infection is 1.1% in nonendemic to 4% in endemic areas [10]. In descending order, the vertebrae, long bone epiphyses, pelvis, skull and ribs are most frequently affected. Soft tissue involvement with calcification is highly suggestive of this disease [11].
Men are involved more than women [9] and the peak age of disease is 21-40 years [10]. Patients with spinal column hydatid cyst may experience lumbar pain, paresthesia, paraparesia and even paraplegia or sphincter dysfunction. Neurological symptoms of this disease may be due to spinal involvement and compression effects on the spinal cord, or direct cord involvement [10].
Although the incidence of hydatid disease has decreased as a result of education and control measures, there are still foci of concern in South America and sporadic cases still occur in the United States, Europe, the Middle East, and Asia [12]. Hydatid cysts may lie dormant in the bone for as long as 40 years and most skeletal hydatid cysts have been detected in adults. Skeletal cystic echinococcosis lesions may be single or multiple [5].
A lucent expansile lesion with cortical thinning is the most frequent radiological pattern, and pathological fractures are common [7].
As hydatid disease of bone remains asymptomatic over a long period, it is usually detected after a pathological fracture or secondary infection or following the onset of compressive myelopathy in the case of vertebral lesions [7].
The differential diagnosis of skeletal cystic echinococcosis includes other infectious lesions (e.g. tuberculosis), fibrous dysplasia and tumors (including simple bone cyst, aneurismal bone cyst, plasmocytoma, osteosarcoma, chondorsarcoma, chondromyxoid fibroma, lymphoma, giant cell tumors, brown tumor and metastases). Diagnosis is primarily based on findings of X-ray and CT scans [5,7]. Whole body bone scintigraphy (WBBS) is able to show the extent and distribution of lesions. WBBS has a high sensitivity but has a poor specificity for osteopathological lesions.
Immunodiagnostic procedures for serum antibody detection such as enzyme-linked immunosorbent assay (IgG-ELISA), the indirect hemagglutination antibody test (IHAT), the latex agglutination test (LAT), the immunofluorescence antibody test (IFAT), immunoelectrophoresis (IEP) and some other tests are used for the etiological confirmation of imaging structures suggestive for cystic echinococcosis or for diagnosis or differential diagnosis in cases of uncharacteristic imaging findings [13].
The initial location of the lesion in long bones is metaphyseal or epiphyseal, later extending to the diaphysis. Plain x ray of the pelvis revealed marked lytic and sclerotic lesions involving the right hemipelvis Figure 3 Plain x ray of the pelvis revealed marked lytic and sclerotic lesions involving the right hemipelvis. Plain x-ray of right femur showed advanced lytic destruction of bone, centered at the proximal two thirds of the right femur Figure 2 Plain x-ray of right femur showed advanced lytic destruction of bone, centered at the proximal two thirds of the right femur. There is also a nailing due to previous surgery.
Potential complications include pathological fracture, infection, and fistulisation of the abscess [7].
Surgery is the treatment of choice for hydatid bone lesions. Many authors have advocated wide resection of the involved bone along with the surrounding soft tissue as the only definitive treatment of the condition, with or without chemotherapy using albendazole or mebendazole [14].
Growth in the direction of least resistance, in time, causes cortical destruction with extension of the cyst into surrounding soft tissues. This condition is rarely encountered in childhood [7]. Hydatid bone disease should be considered in the differential diagnosis of osteolytic lesions, especially in endemic areas. The presence of a periosteal reaction, osteosclerosis, and calcification are not specific for hydatid bone disease [7].
Finally, hydatid bone disease should be considered in the differential diagnosis of osteolytic lesions in radiological imaging as well as single or multiple abnormal uptakes in the whole body bone scan especially among people living in endemic areas.
Whole body bone Scintigram showed multiple foci of increased radiotracer uptake in the lower lumbar spine, the left sacroiliac region and the right knee Figure 4 Whole body bone Scintigram showed multiple foci of increased radiotracer uptake in the lower lumbar spine, the left sacroiliac region and the right knee. In addition there was soft tissue bulging in the right hemipelvis as well as a displaced and disconfigured right femur.