Accuracy of the physical examination in evaluating pleural effusion

Percussion

The chest can be percussed directly with the tips of the fingers of one hand or indirectly by placing a third finger against the surface to be percussed. There are two main techniques used to detect pleural effusions: comparative percussion and auscultatory percussion.

The comparative percussion technique involves comparing the sounds (dullness or hyperresonance) on the right vs the left hemithorax. Dullness may indicate pleural effusion (Figure 3). This is the technique introduced in the 18th century by Auenbrugger and Forbes,²³ who proposed that dullness is always present in a pleural effusion, although it may be difficult to detect if the effusion is bilateral.²⁴

Since other conditions such as consolidation of the lung and atelectasis can also be associated with dullness to percussion, some authors advocate percussion in the lateral supine position to detect a shift in the dullness that would indicate movement of fluid in the chest.²⁵

The sensitivity of comparative chest percussion and its accuracy related to the size of the effusion are unknown. Kalantri et al¹⁰ found that dullness to percussion had a positive predictive value of only 55% but a negative predictive value of 97%, suggesting that the absence of the sign is very helpful in ruling out an effusion.

According to classic textbook descriptions,²⁶ percussive sounds penetrate a maximum of 6 cm (2 cm of body wall thickness and 4 cm of lung), and at least 500 mL of fluid must be present in order to be able to detect an effusion by physical examination.^2,8 Most of these descriptions are based on original studies done in cadavers more than 100 years ago.

The auscultatory percussion technique was first described by Laennec and used to delineate the size of several organs by placing the stethoscope directly above the structure to be outlined, followed by percussion from the periphery towards the organ of interest. The original technique was subsequently modified for the examination of the chest by Guarino.²⁷

This method consists of tapping lightly the manubrium sterni with the distal phalanx of the index or middle finger while listening over the posterior chest wall with a stethoscope (Figure 4). The patient must be in the sitting or standing position with the arms resting at the sides or on the thighs. Percussion is applied with equal intensity over the manubrium sterni while the physician auscultates each posterior hemithorax from top to bottom, comparing the sounds on the two sides and trying to identify dullness to percussion.

In the original description, percussion was limited to the manubrium in an attempt to avoid other solid structures (such as the left ventricle) that would interfere with the transmission of the sounds.²⁷ The authors modified this technique for the detection of pleural effusion (Figure 5): with the patient sitting up and his or her back facing the examiner, a stethoscope is placed approximately 3 cm below the last rib in the mid-scapular line. The physician then proceeds to percuss with his or her free hand (by finger flicking or the pulp of a finger) along three or more parallel lines from the apex of each hemithorax perpendicularly downward toward the base to identify dullness to percussion.¹²

Although auscultatory percussion was used initially to try to detect lung lesions, masses and consolidations, Guarino and Guarino¹² found this technique to be highly effective in detecting pleural effusion. In a prospective blinded study in 118 patients, this method was highly (95%) sensitive and 100% specific in detecting pleural effusion, even in patients with obesity, pneumonia, or other pleural abnormalities. Of note, their findings suggested that auscultatory percussion can detect as little as 50 mL of pleural fluid.

Bohadana et al¹³ compared auscultatory and conventional percussion with chest radiographic findings in 281 patients. They found that auscultatory percussion was 100% sensitive for detecting large pleural effusions.

However, when Bourke et al¹⁴ compared conventional and auscultatory percussion in 21 patients with abnormal radiographs, both methods had low sensitivity (15.4% vs 19.2%) but high specificity (97.3% vs 85.1%, respectively). It is important to mention that in this series only a few patients had a pleural effusion.

McDermott et al¹⁶ compared conventional and auscultatory percussion in detecting pleural effusion in 14 hospitalized patients, using ultrasonography instead of chest radiography as the gold standard for comparison. The findings on auscultatory percussion correlated better with the findings on ultrasonography than did those on conventional percussion. The authors gave no information about sensitivity or specificity.

Kalantri et al¹⁰ found that auscultatory percussion had a sensitivity of 58% and a specificity of 85%.

Auscultation

Originally described by Laennec (who invented the stethoscope),¹⁹ auscultation is perhaps the physical examination technique most used to detect pleural effusion.

Lichtenstein et al¹⁵ performed a study of auscultation in critically ill patients and found it to have a very low sensitivity (42%) but a higher specificity (90%), with an overall diagnostic accuracy of 60%. Of note, compared with chest radiography, auscultatory findings had similar sensitivity but higher accuracy.

Absent or diminished breath sounds strongly suggest an effusion.¹⁹

Egophonism. Laennec also described egophonism as a pathognomonic sign associated with a moderate degree of effusion. The word egophony comes from the Greek “ego,” which means goat; it is used to describe the change in the pronounced sound of E to A. The mechanism responsible for finding this sign in massive pleural effusions is probably upward displacement and compression or consolidation of the lung at the top of the effusion.

However, if the effusion is small, the consolidation will not be large enough to produce this sign. Similarly, other lung conditions associated with large consolidations may produce egophonism without a pleural effusion. Little is known about the predictive value of this sign, and significant interob-server variability needs to be taken into account.²⁸

Pleural rub. Pleural effusions that result from any disease that causes direct inflammation of the pleurae can be associated with a pleural rub. This sound, classically described as rubbing of unoiled leather, is pathognomonic of pleural disease but not of pleural effusion. In fact, a pleural rub will disappear once an effusion develops. Little is known about the accuracy of this finding; in the study by Kalantri et al it had a very low sensitivity (5%) but a very high specificity (99%).¹⁰ The differential diagnosis includes pleuritis, pneumonia, mesothelioma, and tumors that metastasize to the pleura.