Grand Rounds

Ring enhancing lesion in brain and decreasing interferon gamma release assay response

Medical Sciences Department, Pediatric Oncall, Mumbai, India

Address for Correspondence: Dr Ira Shah, 1, B Saguna, 271, B St Francis Road, Vile Parle {W}, Mumbai 400056

Clinical Problem :
A 14 years old boy had recurrent right focal convulsions for past 3 years. MRI brain in December 2013 showed neurocysticercosis stage II in left high parietal region for which he was treated with Albendazole and steroids. In July 2014, a repeat MRI brain showed same size of granuloma. His EEG and video EEG was normal. There was history of multi-drug resistant {MDR} tuberculosis {TB} in 2 siblings of which one died in 2012 and the other was on treatment for same for the past 1½ years. In view of contact with TB, a CSF TB PCR was done which was negative. Mantoux test was negative. Quantiferon Gold test was positive {3.19}. This child was not started on ATT and advised regular follow up. In December 2014, the repeat MRI showed decrease in size of granuloma and Quantiferon gold has decreased to 0.72.

How reliable is interferon gamma release assays {IGRA} for monitoring disease_?

Discussion :
Expert’s opinion: The interferon {IFN} gamma release assays {IGRAs} are based on the fact that T-cells sensitized with tuberculous antigens will produce IFN-gamma when they are re-exposed to mycobacterial antigens. A high amount of IFN-gamma production is then presumed to correlate with TB infection. {1} The QuantiFERON®-TB Gold test {QFT-G} is a whole-blood test for use as an aid in diagnosing M. tuberculosis infection, including latent tuberculosis infection {LTBI} and tuberculosis {TB} disease. IGRAs are dynamic and both conversions and reversions occur when serial testing is done` this has been shown to occur among contacts as well as health care workers. There is no consensus on what the best definition for conversion is – different definitions appear to produce different rates of conversions. QFT reversions were defined as baseline IFN-? ? 0.35 and follow-up IFN-? Less than 0.35 IU, ml. {2} Some reversions may reflect clearing of TB infection {spontaneous or due to treatment}. Some reversions may merely be due to biological variations among IGRA positive individuals, and some reversions may be due to variability in laboratory and test procedures. Other studies suggest that reversions may occur when the mycobacterium enters a dormant state. {3,4} Thus currently IGRAs though may show reversions and conversions on longitudinal follow up of patients, interpretation needs to be with caution.

References :
  1. Andersen P, et al. Specific immune-based diagnosis of tuberculosis. Lancet. 2000
  2. Pai M, Joshi R, Dogra S, Mendiratta DK, Narang P, et al. Serial testing of health care workers for tuberculosis using interferon-gamma assay. Am. J. Respir. Crit. Care Med. 2006; 174:349–355
  3. Hill PC, Brookes RH, Fox A, Jackson-Sillah D, Jeffries DJ, et al. Longitudinal assessment of an ELISPOT test for Mycobacterium tuberculosis infection. PLoS Med. 2007; 4: e192
  4. Helmy N, Abdel latif S, Kamel MM, Ashour W, El Kattan E. Role of Quantiferon TB gold assays in monitoring the efficacy of antituberculosis therapy. Egyptian Journal of Chest Diseases and Tuberculosis. 2012; 61: 329–336

Correct Answers :  yes 43%
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