The chest CT of my patient with “B” symptoms shows hilar mass and mediastinal lymphadenopathy, highly suspicious for lymphoma or malignancy per radiology report. Should I still consider tuberculosis (TB) as a possibility?

Absolutely! TB often mimics malignancy, particularly lymphoma, both clinically and radiographically, even when sophisticated imaging techniques are used.1  

There are ample reports of TB being confused with mediastinal lymphoma, 1-6 with several reports also stressing abdominal TB mimicking malignancy. 7-10 As early as  1949, a  NEJM autopsy study emphasized “the difficulty in differentiating primary progressive TB and some types of lymphoma” and metastatic neoplasms, clinically and radiographically.  Over half-century later, despite major advancement in imaging techniques, TB is often confused for lymphoma or malignancy.

One reason for confusing TB with lymphoma is that primary TB can involve any pulmonary lobe or segment and is often associated with hilar and mediastinal adenopathy. 1 TB may also be overlooked in the differential diagnosis of mediastinal mass that often highlights neoplasms such as lymphoma, thymoma and germ cell tumors. 3 Lack of concurrent pulmonary infiltrates in the presence of mediastinal adenopathy may also veer clinicians away from TB diagnosis. 2,3,6 Unfortunately, even more sophisticated PET/CT scans may not be able to differentiate TB from lymphoma.5,6,9

Besides chest and abdomen, TB can also mimic malignancy in cervical nodes, bones (particularly the spine), bowels, and brain.1,2,6,8,9  To make matters worse, splenomegaly 2,10 and elevated LDH 3 may also be seen with TB and TB may coexist with lymphoma and other malignancies. 7,9,11

One of the best advices I ever received from a radiologist was “Think of TB anytime you think of lymphoma.”

Bonus Pearl: Did you know that TB lymphadenitis is the most common form of extrapulmonary TB with the majority involving the mediastinum? 4

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References

  1. Tan CH, Kontoyiannis DP, Viswanathan C, et al. Tuberculosis: A benign impostor. AJR 2010;194:555-61. https://www.researchgate.net/publication/41509877_Tuberculosis_A_Benign_Impostor
  2. Smith DT. Progressive primary tuberculosis in the adult and its differentiation from lymphomas and mycotic infections. N Engl J Med 1949;241:198-202. https://www.ncbi.nlm.nih.gov/pubmed/18137399
  3. Maguire S, Chotirmall SH, Parihar V, et al. Isolated anterior mediastinal tuberculosis in an immunocompetent patient. BMC Pulm Med 2016;16:24. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4739107/
  4. Tang SS, Yang ZG, Deng W, et al. Differentiation between tuberculosis and lymphoma in mediastinal lymph nodes: evaluation with contrast-enhanced MDCT. Clin Radiol 2012;67:877-83. https://www.sciencedirect.com/science/article/abs/pii/S0009926012001079
  5. Hou S, Shen J, Tan J. Case report: Multiple systemic disseminated tuberculosis mimicking lymphoma on 18F-FDG PET/CT. Medicine 2017;96:29(e7248). https://journals.lww.com/md-journal/Pages/ArticleViewer.aspx?year=2017&issue=07210&article=00005&type=Fulltext
  6. Tian G, Xiao Y, Chen B, et al. Multi-site abdominal tuberculosis mimics malignancy on 18F-FDG PET/CT: Report of three cases. World J Gastroenterol 2010;16:4237-4242. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2932932/
  7. Dres M, Demoule A, Schmidt M, et al. Tuberculosis hiding a non-Hodgkin lymphoma “there may be more to this than meets the eye”. Resp Med Case Rep 2012;7:15-16. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3920344/
  8. Banerjee Ak, Coltart DJ. Abdominal tuberculosis mimicking lymphoma in a patient with sickle cell anemia. Br J Clin Pract 1990;44:660-61. https://www.ncbi.nlm.nih.gov/pubmed/2102179?dopt=Abstract
  9. Gong Y, Li S, Rong R, et al. Isolated gastric varices secondary to abdominal tuberculosis mimicking lymphoma: a case report. Gastroenterology 109;19:78. https://www.ncbi.nlm.nih.gov/pubmed/31138138
  10. Uy AB, Garcia Am Manguba A, et al. Tuberculosis: the great lymphoma pretender. Int J Cancer Res Mol Mech 2016; 2(1):doi http://dx.doi.org/10.16966/2381-3318.123
  11. Nayanagari K, Rani R, Bakka S, et al. Pulmonary tuberculosis with mediastinal lymphadenopathy and superior veno caval obstruction, mimicking lung malignancy: a case report. Int J Sci Study 2015;2:211-14. https://www.ncbi.nlm.nih.gov/pubmed/31138138
The chest CT of my patient with “B” symptoms shows hilar mass and mediastinal lymphadenopathy, highly suspicious for lymphoma or malignancy per radiology report. Should I still consider tuberculosis (TB) as a possibility?

Why is latent tuberculosis usually treated with one antibiotic while active tuberculosis is treated with 2 or more drugs?

Conventional wisdom has been that in active tuberculosis (TB) patients harbor large numbers of replicating Mycobacterium tuberculosis (Mtb), requiring multiple antibiotics to prevent the emergence of resistant mutants. In contrast, Mtb under latent or “inactive” conditions is presumed to have little capacity for mutation due to reduced bacterial replication, thus generally requiring only one antibiotic for preventive therapy.1

However, the assumption that Mtb has a low capacity for mutation in latent TB due to slow bacterial replication has been challenged in recent years. An experimental study in macaque monkeys with latent Mtb infection using whole genome sequencing demonstrated that despite reduced replication, Mtb acquires a similar number of chromosomal mutations during latency as it does during active infection.1

This finding supports the more current and evolving concept of latent TB which assumes diverse mycobacterial growth states, ranging from complete absence of organisms to actively replicating bacterial populations.2 It also explains why, although effective, isoniazid monotherapy may be a risk factor for the emergence of INH resistance in latent TB. 1,3

 Bonus Pearl: Did you know that INH treatment of latent TB in adults is 60-80% protective when given for 6 months, and 90% protective when given for 9 months? 4

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References

  1. Ford CB, Lin PL, Chase M, et al . Use of whole genome sequencing to estimate the mutation rate of Mycobacterium tuberculosis during latent infection. Nat Genet. 2011;43:482-86. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3101871/
  2. Gideon HP, Flynn JL. Latent tuberculosis: what the host “sees”? Immunol Res 2011;50:202-12. https://www.ncbi.nlm.nih.gov/pubmed/21717066
  3. Balcells ME, Thomas SL, Faussett PG, et al. Isoniazid preventive therapy and risk for resistant tuberculosis. Emerg Infect Dis 2006;12:744-51. https://www.ncbi.nlm.nih.gov/pubmed/16704830
  4. Piccini P, Chiappini E, Tortoli E, et al. Clinical peculiarities of tuberculosis. BMC Infect Dis 2014; 14 (Suppl 1):S4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4015485/

 

Why is latent tuberculosis usually treated with one antibiotic while active tuberculosis is treated with 2 or more drugs?

Does corticosteroid therapy impact the results of interferon-gamma release assays—IGRAs— in patients screened for latent tuberculosis?

 

The weight of the evidence to date suggests that immunosuppressive therapy, including corticosteroids, other oral immunosuppressants and anti-tumor-necrosing factor (TNF) drugs, may negatively impact IGRA results.1-5

Some studies have reported daily steroid doses as low as 7.5 mg-10 mg may adversely impact T-cell responsiveness in IGRA. 2-4 In a study of patients with autoimmune disorders, 27% of patients on daily prednisolone dose of 10 mg or more had indeterminate QuantiFeron Gold In-Tube test compared to 1% of patients not taking prednisolone.4

A meta-analysis of the performance of IGRAs (including T-SPOT.TB) in patients with inflammatory bowel disease concluded that these assays were negatively affected by immunosuppressive therapy.5

So, be cautious in interpreting a negative or indeterminate results of IGRAs in patients on corticosteroid therapy or other immunosuppressants.

See also a related P4P post: https://pearls4peers.com/2020/01/20/my-patient-with-rheumatoid-arthritis-might-have-been-exposed-to-tuberculosis-does-immunosuppressive-therapy-affect-the-results-of-interferon-gamma-release-assay-igra-testing-for-latent-tuberculosis/

Bonus Pearl: Did you know that IGRA is not affected by prior Bacillus Calmette-Guerin (BCG) vaccination, a significant advantage over PPD skin tests?

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References

  1. Wong SH, Gao Q, Tsoi KKF, et al. Effect of immunosuppressive therapy on interferon gamma release assay for latent tuberculosis screening in patients with autoimmune diseases: a systematic review and meta-analysis. Thorax 2016;71:64-72. https://thorax.bmj.com/content/thoraxjnl/71/1/64.full.pdf
  2. Kleinert S, Kurzai O, Elias J, et al. Comparison of two interferon-gamma release assays and tuberculin skin test for detecting latent tuberculosis in patients with immune-mediated inflammatory diseases. Ann Rheum Dis 2010;69:782-4. https://ard.bmj.com/content/69/4/782
  3. Ponce de Leon D, Acevedo-Vasquez E, Alvizuri S, et al. Comparison of an interferon-gamma assay with tuberculin skin testing for detection of tuberculosis (TB) infection in patients with rheumatoid arthritis in a TB-endemic population. J Rheumatol 2008;35:776-81. https://www.ncbi.nlm.nih.gov/pubmed/18398944
  4. Belard E, Semb S, Ruhwald M, et al. Prednisolone treatment affects the performance of the QuantiFERON Gold In-Tube test and the Tuberculin skin test in patients with autoimmune disorders screened for latent tuberculosis infection. Inflamm Bowel Dis 2011;17:2340-2349. https://academic.oup.com/ibdjournal/article/17/11/2340/4631016 
  5.  Shahidi N, Fu Y-T, Qian H, et al. Performance of interferon-gamma release assays in patients with inflammatory bowel disease: a systematic review and meta-analysis. Inflamm Bowel Dis 2012;18:2034-2042. https://www.researchgate.net/publication/265093409_Performance_of_Interferon-gamma_Release_Assay_for_Tuberculosis_Screening_in_Inflammatory_Bowel_Disease_Patients
Does corticosteroid therapy impact the results of interferon-gamma release assays—IGRAs— in patients screened for latent tuberculosis?