Is there a role for 99mTc-HMPAO leucocyte scintigraphy in infective endocarditis?
Infective endocarditis is an important disease in developing countries. A combination of clinical findings, typical organisms cultured from blood, and specific echocardiographic features are used to establish the diagnosis. The diagnosis is often difficult because cultures are not always positive and transthoracic echocardiography lacks sensitivity and specificity, leading to delayed treatment or inappropriate therapy. As 99mTc-HMPAO-labelled leucocyte scintigraphy is used routinely to evaluate patients with suspected infectious processes, it was postulated that this technique might also aid in the diagnosis of infective endocarditis in patients with underlying chronic rheumatic heart disease or other valvular disease. Six patients were referred for 99mTc-HMPAO-labelled leucocyte scintigraphy. The white blood cells were labelled according to standard procedures. Whole-body planar imaging and single photon emission tomography of the chest area, with imaging at 30 minutes, 3 hours and 24 hours after the administration of the labelled leucocytes, were performed on all patients. All the scintigrams were negative. The reasons for the negative findings are not entirely clear, but probably reflect the pathological nature of vegetations, which consist mainly of masses of fibrin, clotted platelets and blood cell debris, containing the causative organisms. Leucocytes do not play a major role in the pathological process. Although only six patients were studied, it appears that 99mTc-HMPAO leucocyte scintigraphy is of little value in the evaluation of patients with infective endocarditis. A study after the administration of radiolabelled antibiotics may be of greater value and should be considered in these patients.