What is adrenal tuberculosis?
Located on top of each kidney, adrenal glands produce
steroid hormones
Cortisol, aldosterone, sex hormones and catecholamines. These hormones help
in regulation of metabolism, blood pressure, respond
to stress and immune system suppression. Among all
other endocrine glands, adrenal glands are the most
commonly involved. Adrenal glands may be directly
or indirectly affected by TB infection causing tissue
damage and alteration in endocrine function.
Such a condition is also known as Tuberculous
adrenalitis. Diagnosis of adrenal TB is often overlooked
or delayed. Immunocompromised individuals happen to
be at greater risk for developing adrenal TB, however,
lately individuals with normal immune function are
also found to manifest such infection. Early diagnosis
of adrenal TB is difficult due to no prominent clinical
symptoms at early stages of the disease and clinical
manifestations due to infection may take some years
to become apparent. Study by Lam et al. reported 6%
of overall patients with active TB to have adrenal
involvement. Similarly, adrenal involvement have
been noted in both acute and chronic TB infections.
Immunocompromised patients (AIDS) are more prone
to these infections. An increased risk of adrenal TB
persists in patients with previous history of TB infection
of lungs (pulmonary) or pleural effusion (extrapulmonary).
Alternatively adrenal TB may occur together with the
presence of other extra-adrenal TB .
Pathology and Clinical Presentations
Mycobacterium disseminates to the adrenal gland
hematogenously or lymphogenously where it can reside
without noticeable clinical symptoms for many years.
Adrenal TB is a major cause of adrenal insufficiency
(Addison's disease). Adrenal insufficiency was first
described by Thomas Addison in the year 1855 in
patients with M. tuberculosis infection in the adrenal
glands. Adrenal insufficiency is a condition wherein
adrenal glands do not produce sufficient amount of
steroid hormones. Adrenal insufficiency thus may result
in unspecific clinical features like weakness, fatigue,
anorexia, weight loss, nausea, vomiting, abdominal pain,
hypotension, and skin hyperpigmentation. Symptoms of
adrenal insufficiency occur only when almost 90% of
adrenal gland is destroyed. Hence most of the reported
cases have been found to present adrenal TB only after
10-15 years after initial infection. If left untreated,
adrenal insufficiency due to TB may result in increased
risk of mortality. Hence,adrenal TB needs to be identified
early to facilitate a prompt and aggressive treatment for
complete recovery of adrenal function.
Book TB whole genome sequencing profile
Bilateral involvement of adrenal glands is commonly
seen in patients with adrenal TB. Histological examination
of adrenal glands with TB show a peculiar pattern. These
include presence of granulomas (caseating or non-caseating),
enlarged adrenal glands with peripheral marginal enhancement,
granulomatous inflammation with Langhans-type giant cells,
mass lesions secondary to the development of cold
abscesses
and atrophy of adrenal gland.
Diagnostic Procedures and Findings for Adrenal Tuberculosis
Radiographic imaging serves as a useful non-invasive solution to
facilitate diagnosis of adrenal TB. These include
A) Computed Tomography (CT): It is the go to modality of
choice for identification and characterizing the patterns of
TB involvement in the adrenal gland. Two types i.e. non-
contrast and contrast-enhanced CT are available. Typical
radiologic features include bilateral enlargement of the adrenal
glands (generally asymmetrical) that show peripheral enhancement
and central necrotic areas in acute or sub-acute phases of the TB disease.
In the later stages, the size of the gland diminishes and is replaced
by gross calcifications.
B) Magnetic Resonance Imaging (MRI): It has superior
contrast resolution and tissue characterization potential
can reveal bilateral involvement of adrenal
masses with prolonged enhancement.
C) Positron Emission Tomography (PET): Use of "F
fluorodeoxyglucose guided PET-CT Scan (FDG-PET) can
reveal presence of active TB infection based on the
uptake of FDG in adrenal glands.
What are Adrenal Tuberculosis Diagnostic Tools?
Adrenal Biopsy: Adrenal biopsy is usually the last resort
in patients to prove adrenal involvement by TB when CT
and MRI is not conclusive. Subsequent adrenal biopsy
specimens may reveal necrosis, infiltration of histiocytes
and presence of granulomas. Biopsy will result in a
definitive diagnosis.
Pathology Test: Measurement of basal serum cortisol levels or
an Adrenocorticotropic Hormone (ACTH) stimulation test will aid
in prompt evaulation of adrenal function to rule out adrenal insufficiency.
Recently, focus has shifted more on the use of Interferon Gamma Release
Assay (GRA) which detects both latent and active TB infection. Tuberculin
skin test (Mantoux) is a conventional screening test majorly used for detecting
TB worldwide. Other phenotypic tests such as Acid Fast Bacilli (AFB) smear
(microscopy) and AFB culture and genotypic test such as TB PCR, GeneXpert
or Line Probe Assay may also be used for diagnosis.
Endocrinology and Associated Immunological
Changes
M. tuberculosis is an acid-fast bacterium with highly
impermeable cell membrane. Exposure to
Lipoarabinomannan (LAM), component of the cell wall
of M. tuberculosis, stimulates the human T lymphocytes
to secrete a wide range of cytokines. Thi cells confer
cell-mediated immune responses with the help of
excessive release of cytokines like interferon (IFN-Y, IL-2
and tumor necrosis factor (TNF-a) that facilitate macrophage
aggregation and granuloma formation to contain the TB infection.
On the other hand, Th2 cells are required for immunity against TB
(humoral immunity) and confer more of anti-inflammatory response.
In addition, released cytokines IL-1, IL-2, IL-6 and TNF-a further activate
the Hypothalamic-pituitary-Adrenal axis (HPA axis). The HPA axis is composed
of the hypothalamus, the pituitary gland and the adrenal glands and is a major
regulator of endocrine stress response. Stress induced by TB infection will
manifest an increase in the functioning of the HPA-axis leading to an overall
release of Corticotropin Releasing Factor (CRF) from the hypothalamus.
CRF in turn activates ACTH secretion from the anterior pituitary gland.
ACTH mediates synthesis and release of cortisol (glucocorticoids) from
adrenal cortex. Thus, adrenal glands are maximally stimulated by endogenous
ACTH in response to TB infection leading to high plasma cortisol levels.
Exogenous ACTH may therefore fail to further stimulate the adrenal glands
to secrete Cortisol. Adrenal glands get enlarged not only due to TB infection
but also due to accumulation of ACTH and cortisol in response to stress.
Both Th1 and Th2 cell types regulate each other which is important in the
final balance of host resistance against pathogens. Hormone
dehydroepiandrosterone (DHEA) and its sulfated form (DHEAS),
released from the anterior pituitary gland, have an antiglucocorticoid effect.
Increased cortisol levels and stress shifts the balance towards a Th2
response. This shift, along with age-related changes in DHEAS,
enhances the infectivity of M. tuberculosis. Thus, T cell dysfunction
due to high cortisol and low DHEA-S levels may be responsible for
immunologically-mediated tissue damage in TB. Low levels of DHEAS
often occur in patients with TB, suggesting a role for both increased
cortisol and decreased androgens in the pathogenesis of the disease.
Available Treatment Modalities
Hormone replacement therapy: A long-term low dose
oral glucocorticoid (hydrocortisone) and mineral corticoid
(fludrocortisone) replacement therapy for management of adrenal
insufficiency.
Anti-tuberculous therapy: First line of standard therapy
include use of a 4-drug regimen of isoniazid, rifampicin,
Pyrazinamide and ethambutol for a fixed duration of months.
This may accompany periodic radiological examination to evaluate
the prognosis.
Adrenalectomy: Sometimes adrenal insufficiency due to
TB infection may result in irreversible damage and loss of adrenal function.
In such cases, removal of one (unilateral) or both (bilateral) adrenal glands
is opted with lifelong supplementation of adrenal hormones.
Tuberculosis (TB) remains to be a substantial global health challenge. India is the country with the
highest burden of both, TB and Multidrug-resistant TB (MDR-TB) worldwide and accounts for about
a quarter of the global TB burden. Among the notified cases of pulmonary TB each year, there are an
estimated 79,000 MDR-TB patients. Therefore, along with addressing the disease burden caused by
drug-sensitive TB, it is crucial to tackle the increasing threat of MDR-TB and latent TB infection (LTBI)
as well.
The most important strategy to control TB is early detection and the appropriate treatment of infectious
cases. India is constantly trying to control the two primary routes required to reduce TB incidence and
death, that are diagnosis and treatment. This has brought about several promising advances in diagnostic centre recently, which has led to a significant improvement in the overall scenario.
This article provides an overview on the paradigm shift of TB diagnosis
from conventional microscopy to next generation sequencing techniques.
TB Diagnosis - The Journey
On 24" March 1882, marked as World Tuberculosis
Day, Robert Koch declared the discovery of Tubercle
bacillus. He used the tissues infected with TB to investigate
the bacteria. After several trial and error in the different staining
techniques and the stains used, he found the appropriate technique
which made it possible to observe the rod shaped TB bacilli.
This led to the genesis of TB diagnosis and served as the basis
for the conventional phenotypic procedures.
Laboratory Techniques
Phenotypic Testing Laboratory plays a decisive role in TB diagnosis and
identification, and Drug Sensitivity Testing (DST) of Mycobacterium
tuberculosis (MTB). Laboratories used only microscopy and culture-
based diagnosis for a long time.
Novel Microscopy and Imaging Tools
Sputum Smear Microscopy (SSM) is the primary
diagnostic method for identifying pulmonary TB and is based on
direct visualization of acid-fast bacilli. Conventional SSM has low cost,
limited infrastructural needs, and 20-30 slides can be read per day by
trained microscopists. However, it has highly variable sensitivity (20-80%)
and poor accuracy among individuals with HIV infection. This led to the use
of fluorescent dyes over conventional staining, thus enabling easier reading
at lower magnification. Also, fluorescent microscopy (FM) has about 10%
more sensitivity than light microscopy. But traditional FM microscopes
faced challenges like high cost and dark room requirement which were
overcome by Light Emitting Diode (LED) microscopes like the Primo Star
iLED and CyScope TB Fluorescence Microscope.
Culture-Based Technologies
Cultures are sensitive and can detect even low levels of
MTB. Hence, they are considered the gold standard for
TB diagnosis and DST. However, they have some
important limitations including slow turnaround time,
requirement of bio-safety level 3 environment and trained
personnel for the processing and monitoring of culture specimens.
Solid cultures provide limited clinical value and are time-consuming
whereas the use of liquid culture media allows for more rapid results
along with upto 10% more sensitivity than solid cultures. Liquid cultures
therefore play an important role in identifying microbial resistance.
Automated liquid culture platforms, specifically the mycobacterial
growth indicator tube Bactec MGIT, scans processed MGIT sputum
bottles and determines MTB growth by measuring 0, depletion. Another
system, BacT/Alert 3D measures MTB levels based on CO, accumulation.
However, liquid culture systems are more complex and expensive as
compared to solid culture and can have high contamination rates.
Due to the slow growth of mycobacteria, laboratory
procedures may require 3-4 weeks or longer to yield
results. This made it necessary to search for new and
rapid diagnostic methods.
Molecular Techniques - Genotypic Testing
In the beginning of the 90s, molecular-based diagnosis
became available, providing rapid detection, identification
and DST of MTB. Nucleic Acid Amplification Tests (NAATS)
amplify genome-specific targets through different methods
which include Polymerase Chain Reaction (PCR), Transcription-
mediated Amplification (TMA), Loop-mediated Amplification (LAMP),
Nucleic Acid Sequence-based Amplification (NASBA), and Strand
Displacement Amplification (SDA).
Line Probe Assays (LPAs)
LPAs extract the genomic DNA, select DNA targets,
and label them with biotin to create amplicons. These
amplicons are then applied to strips with specific
oligonucleotide probes. Subsequently, bound amplicons
are detected through attachment of a label and visualization
of a dark band against a scoring chart. These assays allow
for identification of mutations, thereby aiding in DST. However,
due to the high sensitivity of the test, any contamination may
alter test results, and highly trained personnel are required to
run the assay, thus limiting the use of LPAs in reference or
intermediate laboratories.
The Genotype MTBDRplus assay
was endorsed by the WHO for rapid detection of MDR-TB in
smear-positive Samples and culture isolates. Another test,
the Genotype MTB-DRsi, allows for the detection of resistance
of second-line drugs to increase the diagnosis of Extensively
Drug Resistant TB (XDR-TB) and MDR-TB.
Nucleic Acid Amplification Tests (NAATS) Commercial NAATs for
Reference and Intermediate-tier Laboratories.
The first NAATS designed for reference and intermediate-tier laboratories included
Hologic Gen-Probe and COBAS TaqMan MTB test, which targeted highincome countries
and their markets.
Microarray Platforms- TruArray is a microarray platform used for MDR-TB
diagnosis, which is able to distinguish between MTB and Mycobacterium avium through the
use of a single tube PCR reaction, which incorporates a fluorescent label to facilitate visualization.
However, none of the microarray products are adequately validated.
Automated NAATS.
Modular, cartridge-based NAATs simplify and automate all the steps involved in NAATs, and increase
bio-safety and ease of use. Xpert MTB/RIF, the first such TB NAAT utilizes Real Time Polymerase
Chain Reaction and is a combined TB and rifampicin (RIF) resistance assay. All parts of the test are
performed on a single cartridge, which is able to produce results in approximately two hours.
In 2013, Xpert was endorsed by WHO, indicating that it should be used instead of conventional
microscopy and culture for initial diagnosis in adults and children suspected with TB. It was also
endorsed for specific types of extrapulmonary samples i.e., CSF, lymph nodes, and tissues) based
on good accuracy data. Based on a meta-analysis, Xpert has a sensitivity of 89% and a specificity
of 99% for detecting pulmonary TB, and a sensitivity of 95% and specificity of 98% for RIF resistance.
Recently, Xpert MTB/RIF Ultra was launched, a next-generation test with increased sensitivity to
aid TB detection in smear-negative patients.
NAATs for lower-tier Laboratories and Microscopy
Centers- Most high-TB burden countries primarily use Xpert as a rapid DST tool,
mainly due to its high cost. As the technology is challenging to deploy at the
microscopy center level, several tools are being developed that can be used in
lower-tier laboratories, specifically in high-TB burden countries like India. Such
tools include the TrueNAT assay, Genedrive platform, and Easy NAT and are
already on the market but the evidence base is weak, and further evaluations
are necessary for policy development.
Sequencing Methods
Next Generation Sequencing (NGS) methods led to large amounts of DNA data being
processed, profiled, characterized, and evaluated for protein interactions. They enable
both high-throughput and low-cost DNA sequencing, and will be particularly useful for
assessing resistance to newer TB drugs. Shotgun sequencing is being used along with
next-generation methods. NGS also holds a lot of potential for diagnostic and broader
surveillance. It was found by a molecular epidemiologic study that using sequencing
information gave better contact tracing information regarding TB infection compared
to classic genotyping
Whole genome sequencing allows for the identification of de novo
mutations associated with phenotypic drug resistance. For example, a study showed that
second-line drugs were exerting selection effects for mutations which induce drug resistance.
Characterization of these new resistant strains will allow for the design of diagnostics that
can screen for specific mutations. Novel sequencing techniques also allow for heteroresistance
detection, which may be misclassified using non-molecular methods. Along with these tools,
computational algorithms are utilized to analyze data, and cloudbased systems to share data
with larger data repositories.
TB Diagnosis in India - Recent Advances
In 2018, Universal Drug Susceptibility Testing was implemented whereby Drug Resistance and Drug
Susceptibility tests were made available to patients throughout the country, free of cost. Around 24 lakh CBNAAT
tests were performed and approximately 66,000 RIF Resistant cases were detected early.
TrueNat MTB/Rif test is an indigenously developed technology in 2018,
by the Indian firm MolBio Diagnostic Pvt. Ltd. under the "Make in
India" initiative. It is a new molecular test that can diagnose TB
in an hour and test for RIF resistance as well. It can be used as
an initial test for TB, at the same health system level as Xpert
MTB/RIF. This led to further decentralisation and increased
access to highly sensitive molecular tests with augmented
capacity for resistance testing at the peripheral level.
Gaps in TB case finding and the emergence of drug-resistant TB have
created an urgent need for robust and accurate diagnostics. This led
to a paradigm shift to newer tests such as Xpert MTB/RIF that has
proved to be useful in increasing case detection and reducing the
time to treatment. Their use should increase countries to reach the
goal of universal DST. Although these new molecular techniques
are useful for a rapid result, providing preliminary information and
improving patient management, they cannot replace the conventional
methods. Hence, culture-based diagnosis still remains the gold standard
for the diagnosis and follow up on TB.
Focus TB powered by Thyrocare offers MTB detection testing using both
Phenotypic Testing including Microscopy, MGIT culture with DST
and Genotypic Testing including LPA, GeneXpert, TB-PCR at affordable rates.
