Three-phase bone scintigraphy. Asymmetric patterns in the upper extremities of asymptomatic normals and reflex sympathetic dystrophy patients.

Three-phase Tc-99m MDP scans of 61 patients with asymptomatic upper extremities randomly mixed with 17 studies of patients previously diagnosed with reflex sympathetic dystrophy were blindly interpreted by three observers. Asymmetry in any of the phases was recorded and a final diagnostic impression made. Thirteen of 17 reflux sympathetic dystrophy studies were rated abnormal by at least two observers. Mild to striking asymmetry was occasionally seen in all three phases in asymptomatic upper extremities. Twenty of 61 asymptomatic patients (33%) were rated abnormal by at least one observer, and 5 of 61 studies (8%) were rated abnormal by all observers. Asymmetries in normal patients occurred more commonly in the earlier phases, while asymmetry in the delayed images was mild in all but one. Tightening the criteria to exclude mild asymmetry in delayed images resulted in unacceptably low sensitivity for reflex sympathetic dystrophy (29%). Interobserver variability was most prominent in the flow and immediate images. In the diagnosis of reflex sympathetic dystrophy a greater reliance should be placed on the delayed images, which in themselves have an overall sensitivity of 94%. It is important, however, to recognize that occasional mild and rare moderate asymmetries in even the delayed images of normal individuals result in an overall lower specificity of 77%.