To the Editor: Mendelian susceptibility to mycobacterial diseases (MSMD) is a group of inborn errors of immunity characterised by defect in the interferon-gamma (IFN-γ)-mediated immunity [1]. It predisposes patients to infections caused by environmental mycobacteria and other intracellular pathogens [2].

Hereby we report a case of an 8-y-old boy, second born of five children, born of third degree consanguineous marriage, brought with c/o fever on and off and multiple swellings over the neck since past two years. The lymph node swellings increased and ruptured leaving an ulcer. There was no h/o Koch’s contact or BCGosis.

Patient was on Category 1 antitubercular treatment (Cat 1 AKT) for 4 mo in view of presumptive TB. In view of non-resolution of skin lesions and development of chest wall abscess despite being on AKT, prompted us to consider multidrug resistant tuberculosis (MDR TB). There was no growth of mycobacterial and non-tubercular mycobacteria (NTM) from the samples obtained for GeneXpert and Mycobacterial Growth Indicator Tube (MGIT). Skin biopsy done from the edge of wound over neck showed acanthosis with neutrophilic exocytosis and diffuse dermal suppurative granuloma with histiocytosis, likely to be scrofuloderma, hence suggestive of M. ulcerans.

HIV virus was negative. Serum immunoglobulin levels, lymphocyte subset assay and nitroblue teteazolium were normal. Patient was worked up for MSMD, CD212 (IL12β) expression on activated T cells was absent and next genome sequencing revealed IL12RB1 defect [c.493C>T (p.Gln165Ter)] mutation.

Patient was treated with MDR AKT for 18 mo and Clarithromycin for NTM. Flap reconstruction was done for the neck ulcers.

Again after two months’ patient has developed similar lesions. Since interferon gamma (IFNG) is unavailable in India, after resolution of infection patient will be planned for hematopoietic stem cell transplantation (HSCT), which is the only known curative treatment [3].

The child showed evidence of environmental mycobacteria which suggested us to think of primary immunodeficiency and isolating signature organism is always useful clue to evaluate immunological axis [4].