Introduction
Hydatid disease is caused by helminths and is considered the most prevalent among human helminth infections, yet primary skeletal involvement remains rare. Diagnosis can usually occur late, often after significant spread, with spinal involvement accounting for half of the patients. The disease’s dissemination pattern often results in localized malignancy with a poor prognosis. Other names for this condition include hydatid bone disease, osseous hydatidosis, skeletal hydatidosis, and bone echinococcosis.
What Are the Clinical Characteristics of Osteoarticular Hydatid Disease?
Hydatid disease can occur early in any part of the body. The highest incidence of organ infestation is seen in the liver, with almost 50 to 77 % of cases, and in the lungs, with a reported incidence of 8.5 to 43 % of cases. In contrast to this, involvement of the central nervous system has occurred in a range of 3 % of reported cases.
Bone echinococcosis, on the other hand, is relatively infrequent, comprising about 0.5 to 4 % of reported cases. When it does occur, it usually affects the spine, accounting for 50 % to over 60 % of cases, followed by the femur, tibia, humerus, skull, and ribs.
What Is the Pathophysiology of This Disease?
Primary bone hydatid disease is caused by Echinococcus granulosus. It develops when a tapeworm larva settles in bone tissue from the circulation. Unlike in other forms of the disease, pericyst formation does not occur in bone involvement. This will enable the parasite to aggressively spread in irregular branching patterns, particularly along bone canals. The slow growth of multiple vesicles can result in the replacement of osseous tissue between trabeculae.
Over time, the parasite destroys the cortex, spreading the disease to adjacent tissues. While extraosseous cysts may calcify, intraosseous disease rarely shows calcification.
How Does Echinococcus Spread to Cause Hydatid Disease?
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Hydatid disease is caused by the tapeworm Echinococcus.
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The parasite's life cycle involves two hosts.
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Dogs are often the main hosts, yet other carnivores can also act as hosts.
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The adult worm can live in the host's small intestine, attaching to the stomach’s lining with its hooklets.
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Eggs produced by the worm are released into the host's intestine and excreted in the feces.
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Sheep are the primary hosts where the disease progresses.
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The sheep will ingest the tapeworms while grazing on the contaminated piece of land where the excreta is present.
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The eggs can lose their protective layer inside the sheep's intestine, and the embryos will penetrate the intestinal wall.
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These embryos move further into the liver and form cysts.
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The life cycle completes when the definitive host eats the organs of the intermediate host.
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Humans tend to acquire the disease by contact with a definitive host or by consuming contaminated water or vegetables.
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In bone, the disease will grow slowly, but in the liver, these cysts can grow rapidly, reaching 0.39 inches (one centimeter) in size during the first six months and then expanding by 0.7 to 1.1 inches (two to three centimeters) annually, depending on the resistance of the host tissue.
What Are the Signs and Symptoms?
Patients typically complain of pain, swelling, or fractures. In cases of spinal involvement, patients may experience compromised neurological symptoms, including weakness, severe back pain, and disturbances in sphincter function. This parasitic infestation by the tapeworm, though infrequent in the nervous system, presents with various symptoms, posing diagnostic challenges.
How Is It Diagnosed?
Due to a lack of specific clinical features, hydatid disease is often difficult to distinguish from other medical conditions. Medical imaging, especially computed tomography (CT) and magnetic resonance imaging (MRI) plays a vital role in thoroughly assessing the extent and severity of the condition before treatment and in monitoring patient response over time. Early diagnosis is infrequent in this condition. MRI can sometimes be more reliable than a CT. The hydatid disease of bone should be considered a differential diagnosis in osteolytic lesions, though it is infrequent.
What Are the Treatment Approaches?
1. Surgical Approach: In recent times, surgical treatment has been the main approach for osseous hydatid disease. The objective of surgery includes the removal of cysts and surrounding bone, filling bone defects with prostheses or bone grafts, prevention of secondary infections, and minimizing the likelihood of recurrence. Unfortunately, endeavoring these goals completely is rare in this aggressive condition. Most sporicidal agents (agents used to prevent the spread of parasites during surgery) used in treatment fail to remove all microscopic daughter cysts, leading to a high likelihood of recurrence, rendering surgery often only palliative. While long-term survival is possible, eliminating the disease entirely is challenging for the surgeons and may even be impossible at certain times. Effective chemotherapy could substantially improve outcomes in managing this condition. In cases of spinal hydatid disease, the preferred treatment method is laminectomy. However, decompression along the anterior vertebrectomy and fusion also yields positive outcomes.
2. Chemotherapy: The efficiency of chemotherapy in treating hydatid diseases, including bone echinococcosis, depends on factors like drug absorption, metabolism, and bioavailability in both the blood circulation and within cysts. Since 1974, chemotherapy with benzimidazoles such as Albendazole and Mebendazole has been employed in the treatment of human echinococcosis. Albendazole is a relatively recent introduction to treatment options, offering notable benefits such as improved absorption and higher levels of the active metabolite Albendazole sulfoxide (AlbSO) within both cysts and blood circulation. Albendazole is also used in combination with Cimetidine and Praziquantel for treating this disease, and they offer different clinical outcomes.
Conclusion
Hydatid disease is widespread globally. Yet, osteoarticular hydatid disease is uncommon and often misdiagnosed. As it has prolonged clinical latency and there is a lack of specific symptoms, along with the absence of clear radiological signs, the diagnosis of bone hydatid disease can be delayed. Medical imaging plays a vital role in accurately assessing the lesion and planning extensive surgical removal. A more precise diagnosis can be made using MRI, and early intervention can prevent the further spread of this condition. Early diagnosis and hygiene education in endemic zones remain the most important measures to reduce the damage that can occur due to this condition.
