Keywords tuberculosis - mediastinal lymphadenopathy - EBUS-TBNA
Introduction
Mediastinal lymphadenopathy is always a diagnostic challenge and can have multiple
differential diagnoses. Sampling of mediastinal lymph nodes can be done by either
mediastinoscopy, which is a surgical procedure and carries significant risks, or endobronchial
ultrasound-transbronchial needle aspiration (EBUS-TBNA), which is a bronchoscopic
technique. We present the case of a 45-year-old female who presented with isolated
mediastinal lymphadenopathy without lung parenchymal involvement. EBUS-guided sampling
of subcarinal lymph node was done, and the diagnosis of tuberculosis (TB) was achieved.
Case Report
A 45-year-old female patient from the western coast of India presented with a history
of fever for 2 weeks duration along with dry cough. It was associated with loss of
appetite and loss of 5 kg of weight. There was no history of dyspnea, wheeze, or chest
pain. She did not have any history of contact with TB and was not having any preexisting
illness. She consulted a local pulmonologist who asked for contrast-enhanced computed
tomography of the chest. It showed necrotic subcarinal lymph nodes ([Figs. 1 ]
[2 ]). There were no parenchymal lesions in the lung. A bronchoscopic examination was
done, and the endobronchial tree was normal. A conventional TBNA was performed, and
smears showed only blood. The patient was referred to our center.
Fig. 1 CECT thorax (transverse view) demonstrating necrotic subcarinal lymph node. Arrow
denotes necrotic subcarinal lymph nodes. CECT, contrast-enhanced computed tomography.
Fig. 2 CECT thorax (coronal view) demonstrating necrotic subcarinal lymph node. Arrow denotes
necrotic subcarinal lymph nodes. CECT, contrast-enhanced computed tomography.
Differential diagnoses of TB, lymphoma, or metastatic malignancy were considered.
We performed an EBUS examination and visualized a 3Х3 cm necrotic, heterogenous subcarinal
lymph node. EBUS-TBNA was done ([Fig. 3 ]). A rapid onsite cytologic evaluation was performed, which showed clusters of epithelioid
histiocytes against a caseous necrotic background ([Fig. 4 ]). Acid-fast bacilli (AFB) stain was strongly positive ([Fig. 5 ]). Cartridge-based nucleic acid amplification test (CBNAAT) detected Mycobacterium tuberculosis and rifampicin resistance was absent. The patient was started on antitubercular therapy
with a directly observed treatment, short-course-based regimen. Her fever subsided
in a couple of days and appetite improved.
Fig. 3 Endobronchial ultrasound image of necrotic subcarinal lymph node appearing as hypoechoic
structure. Transbronchial fine-needle aspiration needle is seen entering the lymph
node as a white linear structure in right side of image.
Fig. 4 Granulomas comprising of clusters of epithelioid histiocytes and few lymphocytes
against necrotic background (Papanicolaou stain x450X).
Fig. 5 Ziehl–Neelsen staining showing acid-fast bacilli positivity (arrow).
Discussion
TB is a highly prevalent infection in developing countries. According to “India TB
report 2020,” released by India's Ministry of Health and Family Welfare recently,
over 2.4 million TB cases were notified in India in 2019. TB can involve most organs
of the body and can mimic many other conditions. There is a saying “TB can present
like anything except pregnancy.” Isolated mediastinal lymphadenopathy is not unusual
in children but rarely described in adults in the absence of associated parenchymal
lesions.[1 ]
Mediastinal lymph nodes can be enlarged in various pathological conditions like TB,
sarcoidosis, lymphoma, and metastatic lung cancer.[2 ] A sampling of mediastinal lymph nodes is paramount for diagnosing these conditions
and for staging patients with bronchogenic carcinomas. Mediastinoscopy is a surgical
procedure for sampling mediastinal lymph nodes but carries significant risks including
life-threatening bleeding, and injury to trachea, esophagus, and recurrent laryngeal
nerve.[3 ]
EBUS is a bronchoscopic technique that uses an ultrasound probe at the tip of the
bronchoscope to visualize structures within and around airway wall and mediastinum.
It is a minimally invasive and safe procedure that can be performed using local anesthesia
and conscious sedation. Its availability is institution-specific, and expertise is
required to interpret images and obtain diagnostic samples.[4 ] Further, EBUS-TBNA is highly accurate with a diagnostic yield of 92% in diagnosing
mediastinal lymphadenopathy.[5 ]
On ultrasound evaluation with EBUS, heterogenous echotexture of lymph nodes and presence
of necrosis favor diagnosis of tubercular lymphadenopathy.[6 ] On cytologic examination, both TB and sarcoidosis demonstrate granulomatous inflammation.
Presence of caseous necrosis, Ziehl–Neelsen staining demonstrating AFB, detection
of Mycobacterium tuberculosis by CBNAAT, or culture clinches the diagnosis of TB.[7 ] Besides, CBNAAT identifies mutations that confer rifampicin resistance.[8 ] It is important to remember that tubercular lymphadenitis is a paucibacillary disease
and AFB positivity may not be seen in nearly half of patients.[9 ] In comparison, CBNAAT has better sensitivity and increases diagnostic yield to above
70%.[10 ] In remaining cases, the diagnosis will be dependent on cytological findings.
Conclusion
Tubercular lymphadenitis in mediastinal lymph nodes without parenchymal involvement
is rare. EBUS-TBNA is a minimally invasive bronchoscopic procedure that helps in visualizing
and sampling mediastinal lymph nodes. Presence of epithelioid granulomas, caseous
necrosis, and microbiological tests helps in establishing a diagnosis of TB.
