Parasitic Bone and Joint Infections

Osteoarticular parasitic infections are infrequent and related to geographic distribution, ethnic and nutritional factors, and occupation. Hydatid disease, also called echinococcal disease, is the most frequent form of osteoarticular parasitic infections. In humans, echinococcal disease is a medical and public health relevance and occurs in two main forms: cystic echinococcosis (CE) caused by Echinococcus granulosus and alveolar echinococcosis (AE) caused by Echinococcus multilocularis. Bone form accounts for approximately 0.5–4% of echinococcal locations and is potentially the most debilitating form of the disease. Although histopathological lesions of bone CE are well-known and widely reported in the literature, those of bone AE are not well characterized. In typical forms, macroscopic and microscopic diagnoses of echinococcosis are straightforward. Grossly, the bone shows diffuse infiltration by many small, thin-walled unilocular vesicles filled with clear fluid and centered in the medullary cavity. Microscopic diagnosis is established through the observation of protoscoleces, hooklets, parasitic cysts, and their fragments. Unlike CE in other organs, bone CE is an invasive and aggressive disease due to the absence of a pericyst limiting the extension of the lesions. The main problem for the pathologist is the rareness of CE and AE; therefore, he generally has little diagnostic experience with these diseases.