Discussion
Tuberculosis (TB) is a multisystemic infectious disease caused by
various strains of mycobacteria, usually Mycobacterium
tuberculosis. Although pulmonary TB is the most common
presentation of disease; extrapulmonary TB (EPTB) accounts for nearly
20 percent of all cases of TB in immunocompetent hosts, and Tuberculosis
(TB) of the abdomen is seen in 12% of patients with miliary TB
(5)(6).By definition, EPTB describes the occurrence of TB at sites other
than the lung. EPTB can occur in almost any organ system, with the most
common sites of infection being the lymph nodes, pleura, genitourinary
system, and bone (5)(7). Abdominal TB is the sixth most common site for
EPTB, and includes infection anywhere in the gastrointestinal tract,
peritoneum, and intra-abdominal organs such as the spleen, liver, and
pancreas (7).
The clinical presentation of abdominal TB especially pancreatic and
hepatobiliary involvement is often insidious, with nonspecific
constitutional symptoms occurring frequently (5). In a study by Saluja
et al. , the three most common presenting complaints in patients found
to have pancreatic TB were abdominal pain, jaundice, and weight loss
(8). Individuals infected with pancreatic TB may also present with
fever, gastrointestinal hemorrhage secondary to splenic vein thrombosis,
and anorexia (8). If pancreatic TB is suspected, preliminary testing
such as tuberculin skin testing and an interferon-γ release assay
for TB may be negative in patients. Sharma et al. suggest that the
sensitivity of tuberculin skin testing in patients with abdominal
tuberculosis may range from 58 to 100 percent (5). With the wide-ranging
sensitivities of TB screening modalities and an often nonspecific and
varied clinical presentation of pancreatic and hepatobiliary TB,
diagnosis of infection relies heavily on radiologic and histopathologic
findings. In our case, the patient presented with abdominal pain mainly
epigastric associated with jaundice and weight loss. His
interferon-γ release assay for TB (Quantiferon TB Gold) was
positive from the beginning.
Ultrasonography or computed tomography (CT) are often first-line
diagnostic modalities in patients presenting with signs of pancreatic
pathology (2)(5). Ultrasound is often the first investigation used for
diagnosis of pancreatic tuberculosis which may reveal a focal hypoechoic
mass or cystic lesion of the pancreas mostly situated in the head and
uncinate process of the pancreas (2).
CT scan is still regarded as the investigation of choice for pancreatic
pathology (9).CT scan may show hypodense lesion with irregular border in
the head of the pancreas, diffuse enlargement of the pancreas, or
enlarged peripancreatic lymph nodes (9). The presence of hypodense
peripancreatic lymph nodes with rim enhancement, ascites, and/or mural
thickening affecting the ileo-caecal region suggests the pancreatic
tuberculosis (9). Magnetic resonance imaging (MRI) findings of focal
pancreatic tuberculosis include a sharply delineated mass in the
pancreatic head showing heterogeneous enhancement which is hypointense
on fat-suppressed T1-weighted images and shows a mixture of hypo- and
hyperintensity on T2-weighted images (10). In our case, his US showed a
hetero echoic cystic lesion in the pancreatic head, and the CT showed
Pancreatic parenchyma had diffused stranding and hyperechogenic foci,
lastly his MRI showed a relatively well-defined lobulated heterogeneous
T2 hyperintense necrotic lesion involving the pancreatic head and the
caudate lobe of the liver. Techniques for pancreatic biopsy include CT
or ultrasound-guided percutaneous biopsy, surgical biopsy, or endoscopic
ultrasound (EUS) guided fine-needle aspiration (FNA)(2). The American
Joint Commission on Cancer (AJCC) recommends EUS-FNA as the diagnostic
modality of choice in patients with pancreatic masses and has found it
to be the most sensitive and specific method for identifying the
etiology of pancreatic masses (2). The presence of on-site cytology is
imperative in the diagnosis of pancreatic TB, as the immediate
interpretation of the specimen will allow clinicians to request
appropriate cultures (2). Acid-fast bacilli are commonly not seen with
FNA. In a study by Farar et al., nearly 40 percent of patients with
abdominal TB had staining that was negative for acid-fast bacilli (11).
Clinicians should be cognizant of the relatively low yield of FNA
specimens to reveal acid-fast bacilli and thus culture the specimen for
evidence of Mycobacterium tuberculosis (11).In our experience,
the patient underwent EUS-FNA to confirm the diagnosis and for sample
collection, his AFP smear and PCR came positive for acid-fast bacilli
(Mycobacterium tuberculosis) .
Once the diagnosis of abdominal TB has been made, standard anti-TB
therapy appears to be successful in the management of this infection. A
minimum of 6 months of anti-TB therapy is often indicated to achieve
resolution of pancreatic lesions and alleviation of symptoms. Follow-up
CT imaging after treatment may reveal the complete resolution of
pancreatic lesions secondary to tuberculosis and may guide clinicians
regarding the duration of therapy (12).