This article explores the role of FNAC, ZN staining, and CBNAAT in diagnosing tuberculous lymphadenitis, emphasising their importance in avoiding unnecessary surgery and ensuring accurate detection.

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Introduction

Tuberculosis is an important cause of morbidity and mortality in developing countries. Tuberculous lymphadenitis is the most common form of extrapulmonary Tuberculosis. Enlarged lymph nodes are most commonly seen in the neck area and sometimes in the axillary area. Proper diagnosis and prompt treatment of Tuberculosis are very important to improve the overall health of the people of our nation.

This study will emphasise the role of FNAC 1-3 in the diagnosis, avoiding unnecessary surgery and the importance of ancillary techniques like ZN staining and CBNAAT.

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Aims and Objectives

1. To study the incidence of tuberculosis among the cases of superficial lymphadenopathy attending the FNAC laboratory of a tertiary care centre.
2. To study the various cytomorphological patterns of tuberculous lymphadenitis.
3. To emphasise the importance of ZN staining & CBNAAT in the correct diagnosis of tuberculosis.

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Review of Literature 

1. Mycobacterium tuberculosis is a chronic pulmonary and systemic disease. It is a major global health problem and remains one of the most common infectious diseases globally.
2. The source of transmission is humans with active tuberculosis who release mycobacteria into the sputum. Most prevalence is seen in poverty, crowding, malnutrition, immigrants and chronic illnesses such as diabetes, Hodgkin's lymphoma, chronic lung disease, chronic renal failure, alcoholism and AIDS.
3. According to WHO (World Health Organization), an estimated 10.6 million people will suffer from TB in 2021 and it resulted in 1.6 million deaths globally16.
4. The incidence rate in India has decreased from 237 per lakh population in 2015 to 199 per lakh population in 2022. And mortality rate in India decreased from 28 per lakh population in 2015 to 23 per lakh population in 2022.
5. The overall prevalence of TB in Tamil Nadu was 169 per 100,000 people in NFHS-5 (National Family Health Survey-5), compared to 337 per 100,000 people in NFHS-4 15. The prevalence of TB was higher in males than females.

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Pathogenesis

1. The outcome of infection in a previously unexposed, immunocompetent person depends on the development of T-cell-mediated immunity. Thus, these T-cells control the host response to the bacteria and result in the development of cavitation and caseating granulomas.
2. Infection by Mycobacterium tuberculosis proceeds following steps, early in infection replicates unchecked within macrophages to subsequently lead to Th1 cells, which stimulate macrophages to kill the bacteria and cause tissue destruction.

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Fine Needle Aspiration Cytology

1. Lymphadenopathy is a commonly encountered clinical problem which has a multitude of causes. The commonest cause of peripheral lymphadenopathy is non-specific reactive hyperplasia in which the underlying aetiology is infrequently found (probably an asymptomatic inflammatory process). Often associated with infectious mononucleosis, sarcoidosis and tuberculosis.

2. Histiocytes of the epithelioid type forming cohesive clusters are characteristic, Multinucleated giant cells usually of Langhans type. Epithelioid cells are quite distinctive in FNB smears. Their elongated nuclei have a form similar to a boomerang or shoe sole. The nuclear chromatin is finely granular and pale, and the cytoplasm is pale without distinct cell borders.

3. Necrosis or suppuration may or may not be present in granulomatous lymphadenitis.  Caseous material appears granular and eosinophilic in smears and usually lacks recognisable cell remnants. Acid-fast bacilli should, of course, be looked for both in direct smears and culture from the aspirate.

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Differential Diagnosis – Fine Needle Aspiration

• Tumour necrosis
• Sarcoidosis 
• Other cell types resembling epithelioid cells (e.g. endothelial cells/Kaposi’s sarcoma)
• Granuloma in malignant lymphoma and nodes regional to carcinoma with or without metastatic deposits

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Case study

Study centre: MGMGH, KAPV Govt Medical College, Tiruchirappalli.

1. Duration of study: Sept 2023 to August 2024.
2. Study design: Prospective study.
3. Sample size: 512 patients.

Inclusion Criteria

Patients of 10 – 55 years age presenting with palpable lymphadenopathy

Exclusion Criteria

• Patients who do not consent to the FNA test
• Patients with acute fever
• Patients with a skin infection over a swelling

Materials and Methods

1. A prospective study is carried out for a period of one year from September 2023 to August 2024.
2. FNAC was done for 512 patients with superficial lymphadenopathy out of which 152 cases were diagnosed as Tuberculous lymphadenitis.
3. The cytomorphological pattern of these cases is presented along with AFB positivity and detection of Mycobacterium Tuberculosis by CBNAAT.
4. Under strict aseptic precautions, using a 5ml disposable syringe with a 23 -22 gauge needle, aspiration was done.
5. The material was smeared and stained with hematoxylin and eosin, Giemsa stain. Smears are stained by the modified Ziehl-Neelsen technique for AFB.
6. FNAC material was sent for CBNAAT in suspected cases of Tuberculosis.
7. We did not encounter any complications during and after the aspiration procedure.

Observation and Results

1. A total of 512 cases were studied, with ages ranging from 10 -55 years and a male-to-female ratio of 1.5:1. The most common site was cervical followed by axillary lymph nodes.
2. Diagnosis of FNAC of 512 patients was reactive lymphoid hyperplasia, suppurative lesion, epithelioid granuloma without necrosis, epithelioid granuloma with necrosis, only caseous necrosis, metastatic deposits and lymphoma, and their proportion was 58%, 6%, 11%, 5%, 8%,8%, 4% respectively.
3. Out of 152 cases with FNAC findings favouring tubercular lymphadenitis, 88(63%) cases were CB-NAAT positive and the remaining were negative. Ziehl Neelsen's positivity for acid-fast bacilli was found in 40(26%) cases.

Discussion

1. Superficial lymphadenopathy is a very common clinical finding, the aetiology of which can be suspected by clinical signs and symptoms. However, a morphological diagnosis is essential to start anti-tuberculous treatment in cases of TBLN.
2. FNAC is a safe and simple out-patient procedure with high sensitivity in diagnosing tuberculosis in developing countries and can replace excision biopsy.
3. Epithelioid morphology with necrosis was found in all TB cases in the study by Suryadi et al, 9, 2020
4. Apart from studying the cytological details, the material obtained by fine needle aspiration can be used for other tests like AFB staining and CBNAAT to increase the sensitivity of the test.
5. AFB staining is a must for all cases of purulent aspirations.
6. Cartridge-Based Nucleic Acid Amplification Test is very useful in diagnosing equivocal cases of Tuberculosis which could be missed by routine cyto-morphology alone.

Disclaimer- The views and opinions expressed in this article are those of the author and do not necessarily reflect the official policy or position of M3 India.

About the author of this article: Dr. P.V.N.Sarvani is an MD pathologist, working at the Department of Pathology, KAPVGMC, Trichy.