Hiding in plain sight: Diagnosing pleural tuberculosis using lung ultrasound

Abstract

Introduction

Diagnosing pleural tuberculosis can be difficult in patients with ambiguous presentation, especially in resource-limited health centres. Thus, lung ultrasound had been studied as a novel method in helping clinicians to diagnose this condition.

Case presentation

A 48-year-old woman presented with worsening dyspnoea and orthopnoea for one week. She had also experienced weight loss, minimal dry cough and right-sided pleuritic chest pain for several weeks. A chest radiograph showed a right lower zone pleural effusion with no apparent lung consolidation. Lung ultrasound showed a right apical consolidation and right lower zone septated pleural effusion. Pleural fluid investigations showed exudative features of mixed lymphocytic, mesothelial and neutrophilic cellular components. Tuberculin skin test was strongly positive. She was subsequently treated for pleural tuberculosis. One month after treatment, her symptoms had improved considerably.

Discussion

Lung ultrasound has been found to be more effective than chest radiograph in detecting consolidation and diagnosing pneumonia. The portability and efficacy of today’s ultrasound machines, including the handheld types, show that lung ultrasound is a practical, reliable and valuable diagnostic tool in managing pulmonary conditions including tuberculosis, provided that the operators are adequately trained.

Conclusion

Lung ultrasound in tuberculosis is the next frontier for clinicians and researchers.

Introduction

Tuberculosis (TB) is an ancient disease with myriad presentations. The ambiguous nature of some TB patients’ clinical features may pose difficulties for clinicians to diagnose the disease, especially in resource-limited or rural areas. As of late, researchers have begun investigating lung ultrasound (LUS) as one of the radiologic methods in diagnosing the disease.^1,2 Despite the scarcity and limitations of available studies, LUS has shown to be a promising tool in helping clinicians to diagnose tuberculosis in places where more sophisticated radiologic services are not readily available. In this report, we present a case of pleural TB which was diagnosed with the help of LUS.

Case presentation

A 48-year-old woman presented with worsening shortness of breath on exertion and orthopnoea for one week. She also complained of a mild dry cough, loss of appetite and weight loss of 5 kg within one month. She had right-sided pleuritic chest pains for three months which were temporarily relieved with over-the-counter analgesics. Otherwise, she had no fever, chills or night sweats. She was previously healthy and had no known illness. She was a non-smoker and runs a café for a living. Her family members were well and she denied having close contact with anyone with TB. There was no family history of malignancy.

Upon review, she was not tachypnoeic. Her oxygen saturation in room air was 95%. Other vital signs were normal. Lungs examination showed a pleural effusion over the right lower zone. There were no enlarged lymph nodes. The rest of the physical examination was unremarkable.

Blood tests showed normal cell counts, elevated erythrocyte sedimentation rate (ESR) (86 mm/hour) and C-reactive protein (CRP) (89 mg/L). A chest radiograph (CXR) showed a right lower zone pleural effusion (Figure 1). No consolidation was visible.

Figure 1.

Chest radiograph showing a right pleural effusion (arrow).

Lung ultrasound (LUS) using a handheld battery-powered Clarius C3 machine (Clarius Mobile Health, Burnaby, BC V5G 4X5, Canada) showed a septated, hypoechoic pleural effusion over the right lower zone (Figure 2 and Supplementary Video 1). A right pleural tap aspirated 1L of straw-coloured fluid. LUS of the right lung apex, which was done initially to detect pneumothorax after pleural tapping, revealed a small consolidation beneath the pleural lining, absent lung sliding and a suprapleural hypoechoic area (Figures 3 to 5, Supplementary Videos 2 and 3). Pneumothorax was excluded with the presence of lung pulses (Figure 4). Pleural biopsy and computed tomography (CT) thorax were offered which the patient refused.

Figure 2.

Right pleural hypoechoic effusion with septations (arrow). Compressive atelectasis of the right middle lobe (bracket).

Figure 3.

LUS of right supraclavicular region. Oblique view. Shred sign (thick arrow), hypoechoic suprapleural area (arrowhead) and A lines (thin arrows) demonstrated.

Figure 4.

LUS of right supraclavicular region. Longitudinal view. M-mode. Barcode sign (bracket) and lung pulse (thin arrows) demonstrated. Hypoechoic suprapleural area is seen as well (arrowhead).

Figure 5.

LUS of right supraclavicular region. Longitudinal view. Shred sign (thick arrow), hypoechoic suprapleural area (arrowhead) and A lines (thin arrows) demonstrated.

The aspirated pleural fluid investigation was exudative in nature with an elevated protein content of 62 g/L (ratio 0.8) and high lactate dehydrogenase (LDH) concentration (438 mmol/L). Otherwise, pleural fluid glucose and pH were normal. Pleural fluid cytology revealed a mixture of reactive lymphocytes, mesothelial cells and neutrophils. Malignant cells and acid-fast bacilli (AFB) were not detected.

Serial sputum AFB samples were negative. Tuberculin skin test was strongly positive (15 mm). Based on available evidence, the patient was treated for pleural TB. Anti-TB drugs comprising ethambutol, isoniazid, rifampicin and pyrazinamide were started. A month later, her symptoms had improved. Her appetite had improved and she had gained weight. The pleuritic chest pain, cough and breathless had resolved.

Discussion

Tuberculous pleural effusion or pleural TB is among the most common manifestation of extrapulmonary tuberculosis. It accounts for up to 30% of extrapulmonary TB cases in endemic areas.³ In Malaysia, 18.6% of reported extrapulmonary TB cases were pleural TB.⁴ Most patients present with fever, pleuritic chest pain and non-productive cough. Night sweats, chills, dyspnoea and loss of weight were also common. Pleural TB patients may be misdiagnosed as having bacterial pneumonia with parapneumonic effusion, especially if they present acutely. Pleural TB can also present insidiously especially in immunocompromised patients.

In pleural TB, effusions are usually unilateral with right-sided predominance and they can range from anechoic to complex septated echogenic effusions.³ LUS has better sensitivity than CT in detecting septations.⁵ Pleural thickening can also be mistaken for effusion. The presence of the fluid colour sign using colour Doppler imaging will help to differentiate pleural effusions from the former.⁶ Nevertheless, these pleural effusion features are not specific for pleural TB. A pilot study published by Montuori et al.⁷ in 2019 involving 102 TB patients in Italy had found that only apical consolidation and subpleural nodules detected on LUS were significantly associated with pulmonary TB.⁷

Lung parenchymal involvement was seen in up to 50% of pleural TB cases, in which almost all involved the ipsilateral lung. The majority of cases with lung parenchyma involvement were located in the upper lobes which suggest TB reactivation.³ Postero-anterior CXR has limited value in suspected TB patients even when angled specifically for the apices (apical or lordotic view). CT thorax is the preferred imaging modality in these cases.⁸

Diagnosing pleural TB requires a holistic approach which considers the patients’ signs and symptoms, risk factors (immunocompromised state, residents of high burden countries), tuberculin skin test, relevant radiological and laboratory investigations. Despite having high specificity, TB culture and polymerase chain reaction (PCR) have low sensitivity of 50–70% and 62%, respectively. Pleural fluid adenosine deaminase, a highly sensitive and specific investigation, is not widely available in Malaysia.⁹

Lung ultrasound (LUS) has been studied for detecting consolidation and diagnosing pneumonia. Features of lung consolidation on LUS include subpleural consolidation, ‘shred sign’, air alveologram, dynamic air bronchogram, lung ‘hepatization’ and fluid bronchogram.¹⁰ Despite having wider specificity range (78–100%), LUS is more sensitive than CXR in detecting consolidation (98–100% vs. 38–68%). The sensitivity and specificity of LUS in diagnosing pneumonia range from 94 to 97% and 90 to 96%, respectively.⁵ Nevertheless, LUS has its limitations. It is operator dependent, thus inadequately trained operators may provide misleading results.

Our case represents the potential of LUS as being one of the diagnostic modalities in pulmonary TB management. Despite using a handheld battery-powered ultrasound machine, we were able to detect the apical consolidation and septated pleural effusion. Unfortunately, we missed the opportunity to differentiate between loculated pleural effusion and pleural thickening over the apical area. Notwithstanding, both are commonly found in pulmonary TB.⁷

Limited access to radiology services in resource-restricted and rural areas is a challenge for healthcare providers managing TB patients. The advancement of portable battery-powered handheld ultrasound machines and cloud-based image reviewing makes LUS more practical among point-of-care ultrasound (POCUS) providers. The cheaper price of these handheld machines, the ease of machine maintenance and ultrasound gel outsourcing make POCUS adoption more appealing to healthcare administrators. These provide a promising future of LUS utilization expansion and further research in LUS, ultimately for the better care of patients.

Further research is needed and should include investigating the sensitivity and specificity of LUS findings in TB such as apical consolidations and subpleural nodules in pulmonary (both smear positive and negative) as well as extrapulmonary TB. If proven to be efficient, LUS will be a crucial tool in diagnosing the disease, especially in smear negative and extrapulmonary tuberculosis. Ideally, these studies should be conducted in developing high TB burden countries as they would benefit most from the outcome.

Conclusion

LUS is a practical and promising tool in diagnosing pulmonary TB. With adequate training, LUS serves as a valuable and reliable diagnostic tool in managing pulmonary conditions including pulmonary TB. More studies are needed to determine its full utility in diagnosing pulmonary TB, especially in high burden countries.

ORCID iDs

Wan Aireene Wan Ahmed https://orcid.org/0000-0002-9976-1509

Mohd Jazman Che Rahim https://orcid.org/0000-0003-1721-6329