ANSWER 50 This woman has had a sudden onset of pleuritic pain, breathlessness and cough. The physical signs of tachypnoea, tachycardia, raised jugular venous pressure and pleural rub would fit with a diagnosis of a pulmonary embolus. The peak flow of 410 L/min indicates that asthma does not explain her breathlessness. The differential diagnosis would include pneumonia, pneumothorax and pulmonary embolism. The clinical signs do not suggest pneumothorax or pneumonia. Possible predisposing factors for pulmonary embolism are the history of a long aeroplane journey 3 weeks earlier, oral contraception and her work involving sitting for prolonged periods. Other predisposing factors such as intravenous drug abuse should be considered. The ECG shows a sinus tachycardia. The often-quoted pattern of S-wave in lead I, Q-wave and T inversion in lead III (S1Q3T3) is not common except with massive pulmonary embolus. Other signs such as transient right ventricular hypertrophy features, P pulmonale and T-wave changes may also occur. The chest X-ray is normal, ruling out pneumothorax and lobar pneumonia. A ventilation–perfusion lung scan could be done looking for a typical mismatch with an area which is ventilated but not perfused. This result would have a high probability for a diagnosis of pulmonary embolism. A pulmonary arteriogram has been the ‘gold standard’ for the diagnosis of embolism but is a more invasive test. In cases with a normal chest X-ray and no history of chronic lung disease, equivocal results are less common and it is not usually necessary to go further than the lung scan. In the presence of chronic lung disease such as chronic obstructive pulmonary disease (COPD) or significant asthma, the ventilation–perfusion lung scan is more likely to be equivocal and further tests are more often used. In this case a computed tomography (CT) pulmonary angiogram was carried out (Fig. 50.3). This showed a filling defect typical of an embolus in the right lower lobe pulmonary artery.
Figure 50.3 Computed tomography pulmonary angiogram.
A search for a source of emboli with a Doppler of the leg veins may help in some cases, and the finding of negative D-dimers in the blood makes intravascular thrombosis and embolism unlikely. 132