The uptake of (99m)Tc-methylene diphosphonate (MDP) in malignant pleural effusions and, rarely, in nonmalignant pleural effusions has been well documented in the literature. Although the exact mechanism of uptake in these conditions remains unclear, there have been attempts to use the bone scintigraphic features of pleural effusion to predict sensitivity and specificity for malignancy based on pleural fluid cytology. It has been suggested that activity in the chest increases with an increase in

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... effusion volume. We report here, however, a case of malignant pleural effusion, that showed reduced hemithoracic activity in contrast to the expected increased activity. Our experience highlights the need for an open and inquisitive mind to avoid diagnostic pitfalls when confronted with a bone scintigram showing reduced uptake unilaterally or bilaterally in the chest.