BCG lymphadenitis: a potential complication of immune reconstitution following haematopoietic stem cell transplant.

Case reportAn MHC class II deficient 2-year-old boy presented with fever and an enlarging left neck mass 100 days post allogeneic haematopoietic stem cell transplant (HSCT). Fever persisted despite treatment with broad-spectrum β-lactam antibiotics. His BCG vaccination site at presentation was quiescent. Ultrasound showed enlarged cervical lymph nodes. An incisional biopsy of the large nodal mass yielded acid-fast bacilli, identified as Mycobacterium bovis by genome sequencing. Treatment with rifampicin, isoniazid and pyridoxine was started. The mass suppurated (figure 1), before healing concurrently with T-lymphocyte reconstitution at approximately day 130 post-HSCT.edpract;archdischild-2020-320883v1/F1F1F1Figure 1Suppurative BCG lymphadenitis following spontaneous rupture.BCG infection can complicate vaccination in patients with severe combined immunodeficiencies (SCID), including MHC II deficiency1 causing a spectrum ranging from simple adenitis to disseminated disease. BCG immune reconstitution inflammatory syndrome, typically presenting as localised adenitis ipsilateral to vaccination site, is well-described after commencing antiretroviral therapy for HIV and is recognised in patients post-HSCT.2 3 In this case, T-lymphocyte reconstitution restoring the T-lymphocyte mediated response in a previously BCG-vaccinated child is likely to have precipitated both this presentation and its resolution.Early identification of SCID though newborn screening might prevent vaccine administration to patients at risk of complications. QUESTIONS: How is MHC class II deficiency inherited?Autosomal dominantAutosomal recessiveX-linked recessiveMitochondrialWhat role do MHC class II molecules have in the immune response?Costimulation of naïve CD4+ T-helper lymphocytes to prevent anergyInitiation of immunoglobulin class-switch recombination in B-lymphocytesPresentation of antigen to naïve CD4+ T-lymphocytesPresentation of antigen to naïve CD8+ T-lymphocytesWhich method has been proposed for newborn screening for SCID in the UK?Absolute lymphocyte countDetection of T-lymphocyte receptor excision circles (TRECs)Tandem mass spectrometry to detect toxic metabolitesImmunoassay for CD3 and CD45Which is the most appropriate treatment for localised BCG disease in immunocompromised children?Rifampicin and isoniazidSurgical resectionSurgical resection and instillation of isoniazidRifampicin, isoniazid, ethambutol and pyrazinamideWhat common side-effect should patients receiving isoniazid be counselled for?Peripheral neuropathyIncreased seizure frequencyAcute kidney injuryChange in colour of urine Answers can be found on page 2.