Empyema differential diagnosis

Empyema Microchapters
Patient Information
Overview
Classification Subdural empyema Pleural empyema
Differential Diagnosis

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Prince Tano Djan, BSc, MBChB [2]

Overview

Empyema must be diffrentiated from pneumonia, lung abscess, lung cancer and parapneumonic effusions on the basis of the presentation, physical examination findings, chest xray, ultrasound and CT scan findings. For instance on ultrasound, empyema is positive for suspended microbubble sign, air fluid level, curtains sign and loss of gliding sign but these are negative in a lung abscess.

Again empyema is differentiated from a lung abscess in that empyema on CT scan is seen as a lung mass whose cavity is regular with smooth well-defined boundary and shape changes with change in patient's position. Mass may resolve on antibiotics. The split pleura sign is present (most reliable sign to differentiate empyema from lung abscess).

Differential diagnosis

Empyema must be diffrentiated from pneumonia, lung abscess, lung cancer and parapneumonic effusions as shown below:

Variable	Empyema Thoracis	Lung abscess	Pleural effusion	Pneumonia	Lung cancer
Presentation	Variable presentation but may follow long standing pneumonia	Usually has history of aspiration pneumonia, alcoholics, drug abusers, seizure disorder, have undergone recent general anesthesia, or have a nasogastric or endotracheal tube.	Usually follows pneumonia as a complication	presents with fever, pleuritc chest pain, cough	mostly asymptomatic but may have cough productive with hemoptysis and chronic history of smoking
Causes	In general any bacteria can cause an empyema, however different bacteria are associated with different rates of empyema formation.[1]  Common causes include bacteroides, fusobacterium,  haemophilus influenzae, pneumococcal infections, staphylococcus aureus, streptococcus, TB	Lung abscess is commonly caused by bacterial infections and these include bacteroides, peptostreptococcus and prevotella mostly after aspiration	Common causes of transudative pleural effusion include;[1][2][3][4][5] left ventricular failure, Nephrotic syndrome, and cirrhosis, while common causes of exudative pleural effusions[6] are bacterial pneumonia and malignancy	Pneumonia can result from a variety of causes, including infection with bacteria, viruses, fungi, parasites, and chemical injury to the lungs	Direct cause of lung cancers is DNA mutations that often result in either activation of proto-oncogenes (e.g. K-RAS) or the inactivation of tumors suppressor genes (e.g. TP53) or both. The risk of these genetic mutations may be increased following exposure to environmental components example smoking
Laboratory findings	The pleural fluid typically has a low pH (<7.20), low glucose (<60 mg/dL), and contains infectious organisms. Therefore, the diagnosis relies on the presence of pus or organisms on gram stain. A positive bacteria culture from pleural fluid is not needed to make diagnosis of empyema.	Raised inflammatory markers ( eg high ESR, CRP) are usual but not specific	The most widely used criteria is to differentiate between exudate and transudate using the light's criteria. Fluid is exudate when: Pleural fluid protein/serum protein ratio >0.5 Fluid/serum lactic dehydrogenase (LDH) ratio >0.6 Fluid LDH greater than 2/3 the upper limits of normal of the serum LDH	Laboratory findings are non specific example leukocytosis, sputum samples for gram staining and culture. Other tests include urine antigen test, PCR, C-reactive protein and procalcitonin	The laboratory findings are  non specific including: neutropenia, hyponatremia, hypokalemia, hypercalcemia, respiratory acidosis, hypercarbia, hypoxia, and tumor cells in sputum and pleural effusion cytology.
Physical examination	On examination, the following findings may be seen: Lateral chest wall swelling and tenderness, clubbing of the fingernails, dull percussion note, r educed breath sounds on the affected side of the chest, egophony, coarse crackles, increased tactile fremitus, mediastinal shift to opposite side with large empyema	Chest examination shows features of consolidation such as localised dullness on percussion, bronchial breath sound etc. Dental decay is common especially in alcoholics and children. Clubbing is present in one third of patients.	Bulging of the intercostal spaces, decreased chest expansion bronchovesicular breath sounds of decreased intensity, egophony, dullness to percussion, decreased or absent fremitus.	Physical examination increased respiratory rate, low oxygen saturation, difficulty breathing, bronchial breathe sounds, increased tactile fremitus crackling sounds, or increased whispered pectoriloquy.	Physical examination findings are non specific and may include decreased/absent breath sounds, pallor, low-grade fever, tachypnea and cachezia.
CXR	Chest X ray of empyema shows air-fluid level continuos homogenous pattern from the mediastinum to the chest wall forming obtuse angle with the lung parenchyma.	Chest xray shows often unilateral cavity containing an air-fluid level and consolidation of lung parenchyema.	A homogenous opacification is noted at the affected side. The costophrenic angle is obliterated with a meniscus.	CXR shows areas of diffused opacities.	CXR may show lung mass, widening of the mediastinum, atelectasis, or pleural effusion.
Chest ultrasound	Ultrasound in empyema is positive for suspended microbubble sign, air fluid level, curtains sign and loss of gliding sign.	Ultrasound in lung abscess is negative for suspended microbubble sign, curtains sign and loss of gliding sign but air fluid level may be seen,.	Ultrasonography is helpful in making diagnosis of pleural effusion particularly in differentiating effusion from masses. The extended thoracic spine sign on sonography has high sensitivity and specificity for diagnosing pleural effusion. Chest or upper abdominal ultrasound may show subpulmonic effusion as shown below.	Not reqiured unless complicated with empyema	USG is helpful in guiding biopsy, staging and estimating prognosis. It may show hypo- and hyperechogenic masses.
CT scan	Seen as a lung mass whose cavity is regular with smooth and regular lumen, well-defined boundary and shape changes with change in patient's position. Mass may resolve on antibiotics The split pleura sign is present (most reliable sign to differentiate empyema from lung abscess)	Lung mass whose cavity is rregular with undulated lumen, irregular-poorly defined boundary and shape does not change with change in patient's position. Mass may resolve on antibiotics	In most cases CT imaging may not provide additional information that would influence the clinical decision-making process. CT scan shows heterogeneous opacification of the affected side and cardiomediastinal shift to the opposite site in unilateral effusion.	CT findings in pneumonia include:[1] Airspace consolidation Ground-glass oppacities Pleural effusion Hiliar and/or mediastinal lymphadenopathy Bronchiectasis Tree-in-bud appereance	Seen as a spiculated irregular solid mass that does not resolve on antibiotics

References

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