Lymph Node Cytology Raising Suspicion for Evolving Secondary Hemophagocytic Lymphohistiocytosis in a Case of Mendelian Susceptibility to Mycobacterial Disease

Mendelian susceptibility to mycobacterial disease (MSMD) is a rare type of inborn error of immunity (IEI) characterized by increased vulnerability to mycobacterial infection. Evolvement of secondary hemophagocytic lymphohistiocytosis (HLH), a life-threatening condition where hemophagocytosis is seen either in the bone marrow, the spleen or lymph node has been recently recognized in this rare disease. Herein we illustrate the role of lymph node cytology in alerting clinicians to the possibility of evolving HLH in a case of MSMD. A 4-month old male infant presented with genetically confirmed MSMD with homozygous mutation in IFNGR2 (+). He received anti tubercular treatment and best supportive care. At 22 months he presented again with generalized lymphadenopathy, massive splenomegaly, bicytopenia and high grade fever. The cervical node FNAC showed, in addition to ill formed granulomas and acid-fast bacilli, features of hemophagocytosis with engulfed intact lymphocytes, neutrophils, and RBCs within macrophages. A concern for secondary HLH was raised by the cytopathologists and further lab investigations recommended. The patient was clinically monitored for any further morbidity. Since HLH is increasingly being reported as an infectious complication in IEI a high index of suspicion will help in its early detection in MSMD. Lymph node FNAC is a quick and easy tool in diagnosing the same.