Grand Rounds

Abscesses due to injections are generally iatrogenic infections caused by improper aseptic measures or contaminated needles. Pyogenic organisms like Escherichia coli, Klebsiella spp, Staphylococcus aureus are the common agents causing these abscesses.¹ However, rapidly growing non-tuberculous mycobacteria (NTM) like Mycobacterium chelonei, M. fortuitum or even M. tuberculosis can rarely cause sterile caseating abscesses at parenteral injection sites.¹ Most commonly NTM infection is because of contamination with tap water as that is the reservoir of these organisms. It is important for the clinician to know mycobacteria as a probable cause of injection abscesses especially when the aspirate is sterile so that proper anti-tubercular therapy (ATT) or in cases of NTM, treatment with antibiotics after susceptibility testing (against amikacin, doxycycline, fluoroquinolones, Clarithromycin along with first-line antitubercular drugs) can be commenced.¹
Development of abscesses after infection with mycobacteria is dependent on multiple host and pathogenic factors. The susceptibility of the host to develop abscesses or even tuberculosis (TB) is modified by genetic factors (which is one of the reasons why only about 10% of infected individuals eventually develop pulmonary TB).² Hence certain individuals have a genetic predisposition to develop mycobacterial abscesses. Various genetic polymorphisms including chemokine (C-C motif) ligand -2 (CCL-2), interleukin-8 (IL-8), toll-like receptor (TLR), natural resistance associated macrophage protein-1 (NRAMP-1), nucleotide-binding oligomerization domain-containing protein 2 (NOD 2) have been implicated to cause susceptibility to mycobacteria.^3-8 Most of these genes participate in the immune response and hence these polymorphisms alter the immune system and make the individual susceptible to mycobacterial disease. Another rare congenital syndrome responsible for enhancing the susceptibility to mycobacteria is Mendelian susceptibility to mycobacterial disease (MSMD).⁹ Mutations in genes encoding any of the molecules involved in the interleukin 12 (IL-12)/ interferon-gamma (IFN-γ) axis could be responsible.⁹ These genetic polymorphisms may be passed down to the patient’s offspring and may be responsible for a family history of mycobacterial infections sometimes in the form of injection abscesses as seen in the above case. Molecular diagnosis will have to be carried out to rule out the major genetic alterations.¹⁰

References :

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